- Email: [email protected]
Application of Zen sitting principles to microscopic surgery seating
Applied Ergonomics 43 (2012) 308e319
Contents lists available at ScienceDirect
Applied Ergonomics journal homepage: www.elsevier.com/locate/apergo
Application of Zen sitting principles to microscopic surgery seating Kageyu Noro a, *, Tetsuya Naruse b, Rani Lueder c, Nobuhisa Nao-i d, Maki Kozawa d a
Waseda University/ErgoSeating Co., Ltd., Tokyo, Japan Gifu Pref. Research Institute for Human Life Technology, Takayama, Japan c Humanics ErgoSystems, Inc., Encino, CA, USA d Department of Ophthalmology, Faculty of Medicine, Miyazaki University, Miyazaki, Japan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 December 2009 Accepted 31 May 2011
This paper describes the application of an alternative seating concept for surgeons that reflects the research of Zen sitting postures, which require Zazen meditators to maintain fixed postures for long durations. The aim of this alternative approach is to provide sitters with a seat pan with sacral support1 that provides a more even distribution of seat pressures, induces forward pelvic rotation and improves lumbar, buttock and thigh support. This approach was applied to the development of a chair for microscopic surgery. The experimental chair is a seat pan that closely matches the three-dimensional contours of the user’s buttocks. Seat comfort was evaluated by comparing both changes in pelvic tilt and seat pressure distributions using Regionally-Differentiated Pressure Maps (RDPM) with subjective ratings of surgeons while operating in prototype and conventional chairs. Findings include that the sacral support of the prototype chair prevents backward pelvic rotation, as seen in zazen (Zen sitting postures). Preliminary data suggests that the prototype provided greater sitting comfort and support for constrained operating postures than did the conventional chair. These findings support the selective application of concave-shaped seat pans that conform to users’ buttocks and reflect Zen sitting principles. Ó 2011 Elsevier Ltd and The Ergonomics Society. All rights reserved.
Keywords: Seating design Surgical operations Pelvic tilt Sacral support Seat pan Concave chair Seat comfort Pelvis Seat pressure distributions Zen sitting Zazen meditation
1. Introduction 1.1. Western view of seat comfort Pynt et al. (2002) and Pynt and Higgs (2010) trace early attention to sitting postures to Ancient Egypt, pointing to the design of a forward tilting seat from 1500 BC. Even so, much innovation in Western seating has evolved from the findings of Keegan (1953, 1964), who reported that open thigh-torso angles more evenly
* Corresponding author. Tel./fax: þ81 3 3238 5239. E-mail address: [email protected] (K. Noro). 1 The term ‘sacral support’ seems to be commonly used in the U.S., while Japanese people customarily use ‘pelvic support’. The first known use of the term ‘pelvic support’ appeared in Yu and Keyserling (1989). Wu et al. (1998) performed an indepth analysis of the effectiveness of pelvic support for inducing pelvic tilt. In recent years, advances in technology have enabled the direct measurement of pressures on the sacral area that are distinct from those on the pelvic area. In this article, the term ‘sacral’ is used only when the sacral area is identified by palpation. The distinction between pelvic and sacral supports is defined in Section 6.2.1 of this article in relation to Fig. 10. 2 It might be pointed out that Keegan’s research, though brilliant and historically pivotal, would have been considered quite limited today as it represented repeated X-rays of a single young male lying on a horizontal surface.
distribute loads on the spine. Keegan2 focused on pathological problems caused by flexion of the lumbar spine associated with seated postures and proposed design criteria to promote lumbar lordosis. Mandal (1982a,b) expanded on Keegan’s findings and proposed forward tilting seat pans to induce lumbar lordosis. Congleton et al. (1985) espoused the adoption of more neutral forward and back sitting postures. A broad range of new and innovative designs expanded on these Western concepts of seating. Yet, despite the vast body of literature on the topic, we continue to struggle to define seat comfort. Corlett and Bishop (1976) shifted our focus from measuring comfort to discomfort because comfort is more difficult to measure and interpret and also because the two represent not one dimension but rather different constructs. Habsburg and Mittendorf (1980) concluded that subjects’ comfort ratings were based on something other than their own personal experience.3 Analyses by Zhang et al. (1996)
3 These authors found that raters judged seats more stringently in the personal suitability judgment (for me/not for me) than in their ratings on overall seat comfort, suggesting that their comfort judgment hinged upon the projected comfort of an independent and objective user.
0003-6870/$ e see front matter Ó 2011 Elsevier Ltd and The Ergonomics Society. All rights reserved. doi:10.1016/j.apergo.2011.06.006
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
and Helander and Zhang (1997) on the properties of comfort and discomfort led them to conclude that the two constructs measured different dimensions. Kuijt-Evers et al. (2005) proposed a unified field theory for comfort and discomfort. The process becomes even more complex when attempting to evaluate design solutions. Reviews by Lueder (1983) and Corlett (1989) emphasized the lack of objective measures for evaluating sitting comfort; on this basis, the latter suggested instead focusing on the specific context and functional requirements of a seat. In their review, De Looze et al. (2003) noted the dearth of commonly recognized measures and objective findings for sitting comfort. The research on sitting comfort demonstrates a particularly pronounced relationship between seat pressure and comfort. De Looze et al. (2003) concluded that the most consistent predictor of seat comfort related to seat pressure distribution4 and that this relationship was considerably more straightforward than with research measuring muscle activity or spinal profiles. Using a specially designed seat fixture, Goossens (1998) varied pressures and found a strong correlation between the amount of pressure applied to the buttocks and discomfort. Goossens et al. (2005) found subjects were quite sensitive to JND/Just Noticeable Differences in seat pressures at the ischial tuberosities. Compressive loads and displacement of force are affected by our age and the degeneration of the spine (e.g., Pollintine et al., 2004). Even so, Dolan and Adams (2001) noted, “tissue stress probably plays a major role in determining if a given tissue is painful, it is tissue stress rather than overall loading which influences the metabolism of connective tissue cells”. Although backrests may provide important benefits (s.f. Pynt and Higgs, 2010; Rohlmann et al., 2001, Wilke et al., 1999), some emphasized the particular importance of pelvic and sacral support. Grandjean (1973) pointed to the relative superiority of pelvic and sacral support to lumbar supports “since the prolonged maintenance of an upright seated posture with a lordosis of the lumbar spine results in strain on the extensor muscles of the back”. Zacharkow (1988) recommended the provision of pelvic supports just below the posterior pelvic rim in order to support the upper sacrum, pelvis and lumbar spine. Corlett (1999, 2006) emphasized the functional requirements of pelvic support of the buttocks and thighs. Others focused on promoting natural postures through the design of the seat pan. Research by Yu and Keyserling (1989) led to the development of a work chair for sewing with a contoured seat pan that tilted at the front to promote thigh, pelvic, lumbar and thoracicsupport. Rempel et al. (2006) found that garment workers provided with an adjustable height seat pan that tilted at the front experienced a greater improvement in neck/shoulder pain over a four-month period than the control group using an adjustable height flat seat pan. New and innovative designs such as Corlett’s and Gregg (1994) and Corlett’s (2006) Nottingham chair, Opsvik’s Balans chair (Lueder, 2010) and the Bambach Saddle Seat (Gale et al.,1989; see also Gadge and Innes, 2007) emphasized promoting neutral postures through the design of the seat pan. Wu et al. (1998) found that seat pans with pelvic support promoted forward pelvic tilt and induced a more neutral posture than did backrest lumbar supports. Rohlmann and Bergmann (2000) found a padded wedge improved back shape, though not implant loads. Even so, Rohlmann et al. (2001) concluded from their study of a group of patients that opportunities to move are more important than features of the chair.
4 De Looze et al. (2003) reviewed studies that compared seat comfort findings that matched physiological parameters with subjective measures of seat comfort.
309
1.2. Alternative Eastern perspectives of seating It is not surprising that Western assumptions about sitting and seating contrast markedly with traditional Eastern perspectives on sitting. Howes (1957) reviewed the cultural differences in postures and styles of sitting that are specific to gender and nations, particularly between the East and West. Mauss (1979) and Gurr et al. (1998) point to the limitations of Western concepts of posture and seating, which translate poorly to other cultures and may increase associated risk of musculoskeletal disorders. 1.2.1. What is Zen sitting? Noro (2009a,b) reviewed the concept of seat comfort as it applies to Zen sitting, an Eastern way of sitting.5 Noro (2007) surveyed Zen priests’ zazen postures, which reflect the principles of Zazen Buddhism and was developed by the great Master Dogen in the 13th century, who introduced the Zafu posture to promote postural stability. For this reason, Zen monks in Japan now commonly assume Zafu while meditating (Fig. 1) The Zafu sitting style is in marked contrast with those in the West. While Zafu sitting promotes postural stability, Western chair designs aim to facilitate changes of posture. Placing a Zafu underneath one’s buttocks facilitates deep breathing and lengthens the spine by inducing a forward pelvic tilt underneath the gluteus maximus around the sacrum (Fig. 1). In contrast, Western seats commonly attempt to induce pelvic tilt through lumbar supports. 1.2.2. Zen sitting and chairs Noro et al. (2006) contrasted this Eastern view with Western assumptions in seating, based on both medical findings and observations of users interacting with chairs. The implications of medical findings are addressed first. Adams and Hutton (1985) pointed to a lack of reliable evidence that upright sitting benefits the lumbar spine. These authors cited findings of Fahrni and Trueman (1965) from their radiographic experiments on lumbar spines and posited the superiority of kyphotic lumbar spines over postures with lumbar lordosis. They based their opinion on evidence that lumbar disc degeneration is rare among people who habitually sit or squat in postures that flex (flatten) the lumbar spine. In his review, Deyo (1998) reported that numerous studies demonstrate the high prevalence of disk bulges or herniation among asymptomatic people.6 Some findings point to alternate perspectives in chair design. Shimode (1992) noted that the forward inclination of lumbar vertebra is necessary for standing but not sitting. Mandal (1982a,b,1994) suggested that lumbar supports function only when backrests recline. Corlett and Eklund (1984) suggested backrests only promote desirable lumbar curvatures when users lean back; once the flattening occurs during work, “the curve will
5 Zen sitting is only one of many Eastern sitting postures cited by Howes (1957). The lotus position is a particularly important Zazen posture, which Buddha first introduced circa 500 BC. The lotus sitting style differs from traditional Yoga sitting postures and is characterized by symmetrical positioning of the left foot over the right thigh and the right foot over the left thigh. As Buddhism spread from India across the East, the influence of the lotus sitting style expanded across Asia. 6 As one example, Deyo described a “1990 study by Scott D. Boden of the George Washington University Medical Center and his colleagues looked at 67 individuals who said they had never had any back pain or sciatica .MRI found them in onefifth of pain-free study subjects under age 60. Half of that group had a bulging disk, a less severe condition also often blamed for pain. Of adults older than 60, more than third have a herniated disk visible with MRI, nearly 80 percent have a bulging disk, and nearly everyone shows some age-related disk degeneration”.
310
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
Fig. 1. Top row, a Zen Buddhist priest assumes traditional Zazen posture while sitting on a Zafu cushion at the Zennoji Temple in Takayama, Japan. When sitting on zafus, the arrangement between the lower knees and higher buttock positions provide concave postural support that induces forward pelvic tilt. Bottom row, a line of Zen Buddhist priests practicing zazen at a Zazen training hall. Each zafu is occupied by its possessing priest as the primary user.
not push back in”,7 although they did not focus on lumbar support, this general principle appears to be supported by Solomonow et al. (2003) and Solomonow (2009). Using pig cadavers, Brodeur and Reynolds (1990) concluded that lumbar supports have little effect on the contours of the lumbar spine. Rather, they found that the pelvic tilt exerts a primary influence on lumbar curvature. It also tilts the angle of the individual vertebra so that pressures at the front of the discs increase (Adams et al., 1996; Bendix et al., 1996; Corlett, 1999). This conclusion is not fully agreed on. For example, Andersson et al. (1974, 1975) found that in a carefully controlled laboratory environment that lumbar supports reduce loads on the spine. Bendix et al. (1996) reported that lumbar supports on backrests helped reinstate lumbar curves while performing tasks, but not during passive sitting and reading. Another consideration is the use of the backrest. Dowell et al. (2001) found that the majority of workers work with their back
7
Rather, Corlett and Eklund (1984) and Corlett and Gregg (1994) emphasized the central importance of the lumbar support for “transmitting some of the weight of the trunk, head and arms through the chair structure, rather than through the lumbar spine”. Corlett (personal communication 2010) emphasized that the Nottingham seat induces forward pelvic tilt by both its seat pan profile and higher sitting position.
unsupported for most of their work day, although the rates vary with the task. Vink et al. (2007) and a review by Lueder (1994) suggested that users rarely adjust their backrest. Noro et al. (2006) suggested that we rethink prevailing assumptions regarding the centrality of backrests in chair design and develop a theory of seating and sitting that is independent of musculoskeletal systems.
1.3. Eastern approach exemplified by Zen sitting and its supportive evidence Fig. 1 portrays a priest assuming zazen posture while sitting on a traditional zafu cushion from three perspectives. Side view (B) shows the forward sacral/buttocks tilt when seated on the zafu cushion (A). Zazen postures are underpinned by the following characteristics: 1) The sacral support prevents backward pelvic rotation; 2) Increased surface contact support of the buttocks on the seat pan; 3) Reduced pressure between the buttocks and the seat pan, resulting from this increased surface contact; 4) Knees positioned below the buttocks; and
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
5) Zafus customized to fit the dimensions of the individual, particularly the 3D shape of the buttocks and length of the leg. The fifth characteristic in the list above was inherited from the 13th century. Accordingly, each zafu implies the existence of a primary user. Yet only zazen professionals are able to customize zafus to the user’s buttock shape. The lower half of Fig. 2 demonstrates a relationship between the contour appearing in Fig. 1 and the sacral area. Zabutons are commercial versions of zafu, which have been used for some time, which tend to rotate users’ pelvic girdles back (Noro, 2009a,b). A pelvic-support zabuton was developed to overcome this limitation. The upper right of Fig. 2 depicts a commercially available zabuton that provides pelvic support and promotes the first four out of the five previously mentioned features of zazen posture. Conventional and pelvic-support zabutons were experimentally compared. Table 1 compares pelvic tilt angles measured during experimental trials when 44 subjects sat on both pelvic-support and conventional zabutons. Subjects (25 males and 29 females aged between 20 and 71) were instructed to assume a recommended sitting posture with their pelvis rotated forward. Instructions to subjects sitting on the pelvic-support zabuton were associated with an average of 12.5 pelvic tilt, a marked improvement from an average 22 tilt when subjects receiving the same instruction sat on a conventional zabuton. Even so, there was considerable variability in pelvic tilt between individuals that appeared to relate to difference in their physical size. These findings suggest that the pelvic-support zabuton consistently improved the pelvic tilt toward that of the standing position. This beneficial pelvic rotation was evident with both Zen Buddhist priests and subjects from the general population, and can be attributed to both the greater amount of support for the knees and
311
Table 1 Average pelvic tilt measurements in degrees associated with sitting in pelvicsupport and conventional zabutons. Item
Average (median values) Standard error Standard deviation Variance Range Min Max Number F test T test(two-sided)
Pelvic tilt angles (median values in deg.) Pelvic-support zabutons
Conventional zabutons
12.5 1.1 7.2 52.1 27.7 29.8 2.2 44 F(43,43) ¼ 0.47, p < 0.05 T(76) ¼ 4.99, p < 0.05
22.0 1.6 10.5 109.8 45.0 50.9 5.8 44
buttocks and the different elevation between buttocks and both knees (see Fig. 1, side view).
2. Characteristics of microsurgery 2.1. Considerations for microscopic surgery operations Schurr and Buess (2000), Wallace (1999) and Nao-i et al. (2009) associated the surgeon’s increased risk of musculoskeletal disorders with the following characteristics of surgical work: 1. 2. 3. 4. 5.
Sustained foot elevation while operating surgical equipment; Seat pans impact surgeons’ thighs; Inadequate hand support during surgery; An inability to recline or sustain pelvic support; Sustained neck flexion while using microscopes; and,
Fig. 2. A zafu (left) and pelvic-support zabuton (top right), each placed on conventional zabutons in the Zen training hall at Sokoji Temple in San Francisco. A model of buttocks is shown in the lower right area. The circled section points to the sacral area.
312
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
6. Long-term constrained postures. Such restrictive postural demands contribute to the development of acute disorders (Schurr and Buess, 2000; Wallace, 1999). Fig. 3 depicts a surgeon performing eye surgery while using a microscope (circle 5). The surgeon’s seat provides considerably less support of the buttocks than is commonly found in conventional seating. These seats enable surgeons to assume perch-style postures with legs extended (circle 1). The surgeon lacks hand support while operating (circle 3). 2.2. Optimal characteristics of seating for surgeons Schurr et al. (1999) and Schurr and Buess (2000) suggested that surgeons a) assume semi-standing positions to facilitate reach, b) sit on horn-shaped seating that prevents sliding forward and c) use user-friendly foot-pedals. Wallace (1999) suggested tilting the microscope forward a few degrees and the patient’s head forward 45 . Congleton et al. (1985) espoused the adoption of neutral postures to reduce fatigue during surgery. Such suggestions were based on the theories of Mandal (1982a,b), who proposed that seat pans tilt forward to promote lumbar lordosis by opening the thightorso angle per Keegan (1953, 1964) and Mandal (1982a,b). 3. Application of the Zazen concept to the design of surgical chairs It was hypothesized that the application of the theoretical basis for Zen postures would help mitigate postural restrictions associated with microsurgical operations. The characteristics of Zen postures (see Section 1.3) translate into the following design principles.
The different body parts are not equally able to withstand equivalent pressures acting on the tissues. Kishi (2005) reported a negative correlation between the amount of buttock deformation caused by sitting and seating comfort. Further, there was no correlation between the amount of deformation of the thighs and seating comfort. These findings suggest that the optimum pressure distribution may be achieved by introducing different or composite materials and shapes to the seat pan, that adapt the amount of support transmitted to the different buttock and thigh areas. 3.1.2. Second Principle: Adapt peak pressures that result as the sitter interacts with the seat pan in three separate ways (a) Gluteus maximus: The Gluteus Maximus is a major buttock muscle that extends from the end of the thigh muscle toward the lumbar via the ischial tuberosities. This muscle transmits information on seating comfort through its various sensory receptors. Congleton et al. (1985) wrote that buttocks pressures commonly range between 0 and 66.195 mmHg8 and must not exceed 66.2 mmHg. Noro et al. (2005) defined the “sitting comfort zone” as buttock pressures within 50 mmHg, which approximates that of Congleton et al. (1985). (b) Ischial tuberosities: When sitting, the ischial tuberosities interact with the apex of gluteus maximus. Seated pressure distribution measurements are consistently high in this area, located just beneath the torso. (c) Femoral region: In contrast to the buttock muscles, the femoral muscles cannot sustain heavy loads. Unlike the gluteus maximus, these muscles lack sensory receptors yet are sensitive to the sensation of discomfort and materials. The forward bending of the anterior edge of the seat pan (s.f., Yu and Keyserling, 1989) provides a reasonable accommodation.
3.1. Chair design principles 3.1.1. First Principle: Maximize the sitters’ seat pan contact area Larger surface contact areas provide a more even distribution of seat pressures over the pelvic girdle, resulting in a lower force per unit area.
3.1.3. Third Principle: Design the seat pan to emulate the 3-dimensional shape of the user’s buttocks Chair seat pans and backrests often function independently. In contrast, the Eastern perspective of the chair views this support as a “shell” that considers the seat and back in conjunction. Closely related to this perspective is the concept that the surgery chair ‘shell’ should emulate the 3D shape of the specific user surgeon’s buttocks as they assume their working postures. In addition, the angle between the shell and floor should reflect the Zen sitting principle that the knees be lower than the buttocks. 3.1.4. Fourth Principle: Adapt the floor-sitting tools to the primary users Since the 13th century, Zen sitting has traditionally dictated that floor-sitting tools (zafu or zabuton) are optimized to each user’s physical characteristics. This approach is particularly typical when achieving what we would now consider ergonomic objectives of this approach.
4. Development process 4.1. Formation of a research project team The prototype chair was not developed by a manufacturer but rather through a participatory approach with a team comprising ergonomists, surgeons, a specialist in cushioning, a clinical
Fig. 3. Ophthalmic surgery while using a microscope.
8 To maintain consistency, mmHg values are converted here from the original text of 0e1.28 psi from the original author (Congleton et al., 1985)
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
313
technologist and specialists in subjective evaluation. An ergonomist served as the team leader. Table 2 lists project development stages. 4.2. Production of prototype chair Table 2 lists the steps followed to develop a prototype chair. In creating the prototype, 3D contours of buttocks, sacral area and thighs of the primary user were measured during surgery. A detailed description of this stage is beyond the scope of this paper. Fig. 4 compares the prototype model created in Phase 2 of Table 2 with a conventional chair. The prototype chair (A) features a shell that emulates the 3D shape of the primary user’s buttocks. Its concave-shaped shell was cushioned and covered with a surface material. The curved lines represent typical contours. In contrast, the conventional chair (B) provides a convex seat pan. Though it resembles a stool, for the purposes of this paper it was named a chair so as to comply with the official designation used in ophthalmic surgery. 5. Experiments Experiments were composed of a trial session and ensuing fullfledged experiments. The trial session was conducted by Sub. A, the surgeon who oversees the operation room, who permitted the use of the surgical prototype chair. For the full-fledged experiments, all subjective and objective measurements were performed in the operation room. 5.1. Subjects Eleven subjects (7 males and 4 females) served as experimental participants. Among these, subjects A through D were surgeons (Sub. D only participated in some objective measurements). Subjects E through K were assistant doctors. Percentile values for subject statures ranged from 14.7 to 84.2 (females) and 11 to 84.4 (males) (Kouchi et al., 2000). Measurements were carried out during ten surgical operations.
Table 2 Stages of project development. Phase 1: Preliminary study and formation of Project team Initial review of Zen sitting theories and its supportive evidence Considerations for Microscopic surgery operations Characteristics of microsurgical work Application of the Zazen concept to surgical chair design Form Project team Phase 2: Creation of 3D prototype chair and experiments Creat 3D prototype chair Trial session by primary user to examine feasibility of prototype chair for use in operating room Perform trial session by primary user (Sub A) Experiments Subjective measurements 1 Evaluation of the relative comfort 2 Body parts discomfort 3 Paired comparison of two chairs Objective measurements 1 Pelvic tilt 2 Body pressure Phase 3: Analysis of findings and future work Result of subjective ratings Result of objective data Feasibility evaluation for commercial versions Proposal of a physiological model for seat comfort
Fig. 4. The concave-shaped prototype (A), conventional chair with a convex seat pan (B), and corresponding sitting postures assumed by the surgeon (Sub. A).
5.2. Subjective evaluations Thirteen questionnaires on a 5-point scale were given to subjects asking their sense of comfort as they got seated to compare two types of model, prototype and conventional. Surgeons and assistant doctors served as the subjects. Surgeons were asked about their impressions felt on their body parts, sacral, ischial, and thigh areas, prior to and following surgery. Lastly, surgeons and assistant doctors were requested to compare the prototype and conventional chairs to determine which was better. ANOVA was used to analyze rating. For all figures in this paper, responses are digitized as follows: Definitely not ¼ 2 Somewhat not ¼ 1 Neutral ¼ 0
Somewhat yes ¼ 1 Definitely yes ¼ 2
5.2.1. Objective measurements 5.2.1.1. Pelvic tilt. Fig. 5 depicts the experimental device used to measure pelvic tilt. Pelvic tilt was measured using a patented gyroscope9 that measures 3D pelvic rotation with pitch and roll ranging between 60 and þ60 , respectively (Wu et al., 1998). In
9 Japan Patent Office Certificate (2007): Title of invention, a pelvic-angle measuring device; Inventor, Kageyu Noro; Patent no. 3928103 2004.
314
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
Fig. 5. Measurement of pelvic tilt in the operation room; A: The dashed arrow denotes negative pelvic tilt; B: Experimental Gyroscope; C: Device mounted under surgical gowns.
Fig. 6. Experiment using a pressure-imaging pad; 1: Sensor; 2: Sensor placed on chair; 3: Surgeon seated; 4: Measurement of pressure distribution.
this paper, pitch angles relevant to forward pelvic tilt are assumed to take positive values.10 5.2.1.2. Body pressure distributions. Fig. 6 demonstrates the experimental use of a pressure-imaging pad. A polyester pressureimaging square-type pressure measurement pad 45 cm in side length was embedded with 36 36 cells. It measured a sampling rate of 10 frames/s with pressure ranging from 0 to 220 mmHg. Accuracy of measurement was approximately 10% (10 mmHg).
10 The terms tilt and rotation represent different expressions of the same phenomenon in pelvic movements. While positive and negative indicators of crossdirectional tilt or rotation are arbitrary, we established baselines for anterior tilt or rotation as described by Wu et al. (1998).
Calibrations were conducted as appropriate. A clinical technologist identified the locations of surgeons’ buttocks, thighs and sacrum through direct palpation.
6. Results of experiments 6.1. Result of subjective ratings A trial session to examine the experimental chairs and protocols (including subjective and objective measurements) was conducted by primary user Sub. A as he worked at the clinic. The subject rated the prototype as superior to the conventional chair. The following is the result of subjective ratings taken about one year after the trial session.
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
Fig. 7. Ratings of body part discomfort at the sacrum, ischial tuberosities and thighs.
315
The primary user Sub. A rated all body part discomfort scores as 2 points while sitting in the prototype chair for both before and after the operations (See Fig. 7). On the contrary, the scores given by the other subjects increased to 2 points for each body area after the prototype chair was used, 1 point above the 1 point rating prior to its use. The reason is that before the use of the chair, the evaluations were conducted with the positional relationship between surgeons and the surgical table remaining rough and the evaluations after its use reflected the fact that the positional relationship became exact in the course of surgical operations. This reason was revealed by surgeons’ subsequent comments. The primary user (Sub. A) rated the slide-resistance of the prototype chair 2 points, compared with other subjects’ average ratings of 0.5 point. The distance between Sub. A’s feet and foot switches was optimal. In contrast, other subjects noted that the gap between the foot switches caused them to slide forward. Paired comparisons associated with the two chairs are summarized in Fig. 8; the prototype was strongly preferred to the conventional chair. 6.2. Analysis of objective data
Fig. 8. Paired comparisons: Surgeons and assistant doctors were requested to compare two types of chairs to determine which was better.
Fig. 7 depicts subjective body part discomfort ratings for the sacrum, ischial tuberosities and thighs associated with the use of the prototype chair. The surveys included questions about the slideresistance of the chairs while operating.
6.2.1. Static measurement 6.2.1.1. Preliminary trial test. Fig. 9 summarizes objective measurements conducted during a preliminary trial session that lasted 50 min with primary user Sub. A. 6.2.1.2. Experimental testing. Objective measurements were performed approximately one year after the initial testing. The evaluation of the contact surface between a surgeon and the prototype chair was conducted by measuring the subjects’ pressure distribution during work prior to surgical operation. Fig. 10 compares body pressure distributions between the prototype and conventional chairs.
Fig. 9. Basic statistical data associated with contact pressures. A measuring instrument used is different from that for most charts shown in Fig. 10.
316
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
Fig. 10. Pressure distribution measurements of three surgeons performing surgery while seated on the prototype and conventional chairs.
Fig. 10 depicts the six areas with rectangles that identify the surgeon’s buttocks, thighs and sacrum through palpation by a clinical technologist. This approach measures the Regional Differentiation of Pressure Distributions associated with the “Regionally-Differentiated Pressure Maps” (RDPM) (Noro, 2009a). The pressure maps and table in the figure both represent stable “moment to moment” values during surgery. Fig. 10 points to clear differences between two types of chairs in the size of pressure distribution, peak pressures and their associated locations. These distinctions are presumed to be associated with the differences between the concave-shaped prototype and a conventional chair with a convex seat pan. Note that some cells inside the Fig. 10 tables are left blank, as the conventional chair lacks sacral and lateral support. Area A in Fig. 10 represents sacral support, while pelvic support corresponds to the entire areas except for the thigh area. 6.2.2. Changes in pelvic tilt Pelvic tilt was measured as Sub. A performed vitreous surgery while seated on the prototype chair. Fig. 11 depicts changes of pelvic tilt throughout the surgery.
Fig. 11 suggests that, following surgical preparation, the surgeon assumes a fixed posture for approximately 590 s while operating. The subject maintains a nearly constant pelvic tilt (about 10 backward tilt relative to the arbitrarily defined 0 reference point while standing). Postures often exceed 20 backward pelvic tilt.
Fig. 11. Changes in pelvic tilt during a session of vitreous surgery that lasted 1 h and 3 min from 9:11 to 10:14 taken from Sub. A (seat height: 44.5 cm) using the prototype chair. Steps A through E include the following: A: start of the vitreous surgery, intraocular procedures. BeC: preparation of the vitrectomy machine, procedures outside of the eye. C: re-start of the vitreous surgery. D: end of the vitreous surgery, scleral wound closure (outside of the eye). E: end of the surgery.
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
317
Table 3 Summary of objective data.
These correspond to surgeon’s look-back actions at the instrument table. It is also possible that some measurements might inadvertently measure the surgeon at rest. Noro (2009a,b) demonstrated that pelvic tilt for conventional chairs often exceed 19 . This suggests that, as with zazen, the sacral support is effective at preventing backward pelvic rotation.
the prototype chair was rated more comfortable than the conventional chair, with further increases in comfort ratings after surgery (See Fig. 8).
6.2.3. Summary of objective data Table 3 summarizes the objective experimental data collected during ten surgeries, as well as the surgeons, chairs used, and averaged values for duration, pelvic tilt, mean pressures and contact areas during the experimental sessions. Differences in pelvic tilt between prototype and conventional chairs were not significant (see Table 3). Pelvic tilt measurements of some subjects who sat on the prototype chair approached zero relative to the standing posture, while others such as 15.8 (Sub. A) and 18.4 (Sub. D) are comparable to the 19 pelvic tilts associated with sitting on a folding chair (Section 1.2.2). This finding suggests that further investigation is needed to evaluate the potential for subsequent versions of the prototype chair to consistently promote better sitting postures. Further, the size of the body support area of the prototype chair ranges between 1318 cm2 for Sub. A and 868 cm2 for Sub. D,11 are significantly greater than that when the conventional chair was used12 (702 cm2 for Sub. B and 558 cm2 for Sub. C) for the same kind of surgery and at the same surgical table. Given this, the objective data are consistent with the subjective data. This difference in body size support area and also in peak seated pressure values were statistically significant. With the exception of pelvic tilt data, the objective data consistently reflected subjective findings;
7.1. Verification of the hypothesis
11 12
Measured during surgery sessions 6 and 8. Measured during surgical sessions 9 and 10.
7. Discussion
This paper described the development of a special purpose chair that aimed to mitigate the physical loads associated with surgeon’s work in fix postures required during microscopic surgery operations (described in Section 2.1). Its development was based on traditional concepts adopted for Zen sitting. That is, the experimental hypothesis reflected criteria 1) through 5) in Section 1.3. The application of this concept emphasized both the maximization of contact area of a seat and the modification of peak pressure values around the gluteus maximus, ischial tuberosities and femoral regions. The prototype chair greatly increased the extent of the sitter’s contact area of support (
318
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
pressure distributions acting on muscle sites that were identified through palpation by a clinical technologist and defined as the boundaries of Regionally-Differentiated Pressure Maps (RDPM). The RDPM provides a more detailed analysis of pressures imposed on human bodies than has previously been demonstrated in past studies by Congleton et al. (1985) and Noro et al. (2005). As shown in Fig. 10, seated pressure distributions on the femoral regions of D-L and D-R for the prototype chair are considerably lower than those of the conventional chair. Findings of Schurr and Buess (2000), Wallace (1999) and Nao-i et al. (2009) suggest that the implementation of characteristics of zazen postures, particularly the criteria 4 “sufficiently low buttock contact pressure” (Section 1.3), might theoretically mitigate some extent of risk of incurring musculoskeletal disorders. Even so, as shown in Fig. 10, measured pressure distributions of Area B of the prototype were higher than expected. This concern might possibly be circumvented through further changes in cushioning materials at this area to enhance seating comfort. The findings in this paper also emphasize the importance of concave surface that support the buttocks and sacrum for comfort. Schurr et al. (1999) and Schurr and Buess (2000) suggested that the ideal surgery chair would enable a surgeon to assume semi-standing positions that facilitate reach and foot-pedal operations while sitting on a horn-shaped seat that prevents forward sliding actions. The Zen-based approach reflects these recommendations by Schurr and Buess (2000).
7.2. Primary user approach Traditionally, ergonomics specialists commonly establish adjustment ranges by identifying percentile values of relevant anthropometric dimensions of the user population. Although this approach sometimes leads to design solutions that are less than optimal for certain individual users, it aims to serve as a best overall compromise for the general population of users. Naturally, this research does not suggest that such approaches are inappropriate for
Fig. 12. A physiological model for seat comfort.
conventional purposes and general use. The primary user approach aims to optimize designs for selected individuals whose work requires further tailoring. Noro (2009a,b) previously addressed considerations associated with mass production of concave-shaped seating. 7.3. A physiological model for seat comfort Fig. 12 depicts a seat comfort model that reflects the design theory described in this article. The intent of this model is to suggest an alternative approach that incorporates physiological and objective data for evaluating seat comfort. In particular, the sensory nerves shown in the buttock and thigh regions A and B, respectively, in Fig. 12 are associated with initial sensations of comfort or discomfort which are subsequently verbalized after processing by the central nerve system. This model is proposed as an alternative physiological model for seat comfort. Acknowledgments The authors thank Shinichi Watanabe at Sanko Urethane Co., Ltd. and Masato Kakudo at Hachido Co., Ltd., and Kazutoshi Takagi at Takagi Seiko Co., Ltd. for their generous sponsorship and manufacture of the prototype chairs. They are indebted to Shunji Yamada at ErgoSeating Co., Ltd. for his invaluable participation, as well as for the invaluable insight and comments by Jenny Pynt at Charles Sturt University. Finally, the author Kageyu Noro thanks M.C. Mandal for his contributions to the field of ergonomics, and for his personal guidance over 25 years ago. References Adams, M.A., Hutton, W.C., 1985. The effect of posture on the lumbar spine. Journal of Bone and Joint Surgery 67-B (4), 625e629. Adams, M.A., McMillan, D.W., Green, T.P., Dolan, P., 1996. Sustained loading generates stress concentrations in lumbar intervertebral discs. Spine 21 (4), 434e438. Andersson, B.J., Ortengren, R., Nachemson, A.L., Elfstrom, G., Broman, H., 1975. The sitting posture: an electromyographic and discometric study. Orthopedic Clinics of North America 6 (1), 105e120. Andersson, B.J.G., Ortengren, R., Nachemson, A., Elfstrom, G., 1974. Lumbar disc pressure and myoelectric back muscle activity during sitting. Scandinavian J Rehabilitation Medicine 6, 104e114. Bendix, T., Poulsen, V., Klausen, K., Jensen, C.V., 1996. What does a backrest actually do to the lumbar spine? Ergonomics 39 (4), 533e542. Brodeur, R.R., Reynolds, H.M., 1990. Passive mechanics of the lumbo-pelvic spine for erect and slumped seated postures. In: Proceedings of the May 1990 International Conference on Spinal Manipulation. FCER, Arlington, Virginia, pp. 190e193. Congleton, J.J., Ayoub, M.M., Smith, J.L., 1985. The design and evaluation of the neutral posture chair for surgeons. Human Factors 27 (5), 589e600. Corlett, E.N., Eklund, J.A., 1984. How does a backrest work? Applied Ergonomics 15 (2), 111e114. Corlett, E.N., 1989. The Ergonomics Society. The Society’s lecture 1989. Aspects of the evaluation of industrial seating. Ergonomics 32 (3), 257e269. Corlett, E.N., 2006. Background to sitting at work: research-based requirements for the design of work seats. Ergonomics 49 (14, 15), 1538e1546. Corlett, E.N., 1999. Are you sitting comfortably? International Journal of Industrial Ergonomics 24 (1), 7e12. Corlett, E.N., Bishop, R.P., 1976. A technique for assessing postural discomfort. Ergonomics 19 (2), 175e182. Corlett, E.N., Gregg, H., 1994. Seating and access to work. In: Lueder, R., Noro, K. (Eds.), Hard Facts About Soft Machines; The Ergonomics of Seating. Taylor and Francis Publishing, London and Philadelphia, pp. 335e345. De Looze, M.P., Kuijt-Evers, L.F., Van Dieen, J., 2003. Sitting comfort and discomfort and the relationships with objective measures. Ergonomics 46 (10), 985e997. Deyo, R.A., August 1998. Low-back pain. Scientific American (Japanese version). Nikkei Science 279, 46e53. Dolan, P., Adams, M.A., 2001. Recent advances in lumbar spinal mechanics and their significance for modeling. Clinical Biomechanics 1, S8eS16. Dowell, W.R., Yuan, F., Green, B.H., 2001. Office seating behaviors: an investigation of posture, task, and job type. Human Factors and Ergonomics Society Annual Meeting Proceedings 45, 1245e1248. Fahrni, W.H., Trueman, G.E., 1965. Comparative radiological study of the spines of a primitive population with North Americans and Northern Europeans. Journal of Bone and Joint Surgery [British Volume] 47B (3), 552e555.
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319 Gadge, K., Innes, E., 2007. An investigation into the immediate effects on comfort, productivity and posture of the Bambach saddle seat and a standard office chair. Work 29 (3), 189e203. Gale, M., Feather, S., Jensen, S., Coster, G., 1989. Study of a workseat designed to preserve lumbar lordosis. Australian Occupational Therapy Journal 36, 92e99. Goossens, R.H.M., 1998. Measuring factors of discomfort in office chairs. In: Scott, P.A., Bridger, R.S., Charteris, J. (Eds.), Global Ergonomics, vol. 2. Elsevier, Amsterdam, pp. 371e374. Goossens, R.H., Teeuw, R., Snijders, C.J., 2005. Sensitivity for pressure difference on the ischial tuberosity. Ergonomics 48 (7), 895e902. Grandjean, E., 1973. The Physiological design of household furniture (Chapter 4). In: Ergonomics of the Home. Taylor & Francis, Ltd., London, pp. 95e135. Chapter 4. Gurr, K., Straker, L., Moore, P., 1998. Cultural hazards in the transfer of ergonomics technology. International Journal of Industrial Ergonomics 22 (4e5), 397e404. Habsburg, S., Mittendorf, L., 1980. Calibrating comfort: systematic studies of human responses to seating. In: Oborne, D.J., Levis, T.A. (Eds.), Human Factors in Transport Research. Academic Press, New York. Helander, M.G., Zhang, L., 1997. Field studies of comfort and discomfort in sitting. Ergonomics 40 (9), 895e915. Howes, G., 1957. The anthropology of posture. Scientific American 196, 123e132. Keegan, J.J., 1953. Alterations of the lumbar curve. Journal of Bone and Joint Surgery 35, 589e603. Keegan, J.J., 1964. The medical problem of lumbar spine flatting in automobile seats. In: Booklet 838A 1e12. Society of Automotive Engineering. Kishi, S., 2005. Evaluation of sitting comfort based on hysteresis characteristics of human body and cushion. In: Master’s Thesis Waseda University, pp. 39e40. Kouchi, M., Mochimaru, M., Iwasawa, H., Mitani, S., 2000. Anthropometric Database for Japanese Population 1997e98. Japanese Industrial Standards Center (AIST, MITI). Kuijt-Evers, L., De Looze, M., Vink, P., 2005. Theory of comfort. In: Vink, P. (Ed.), Comfort and Design. CRC Press, pp. 13e32. Lueder, R., 1994. Adjustability in context. In: Lueder, R., Noro, K. (Eds.), Hard Facts About Soft Machines; The Ergonomics of Seating. Taylor and Francis Publishing, London and Philadelphia, pp. 25e35. Lueder, R., 2010. Ergonomics review of the literature relevant to Balans seating. Sponsored by VarierUSA.com. Downloaded 9/15/2010 at. www.humanics-es. com/ergonomics.htm#sitting. Lueder, R.K., 1983. Seat comfort: a review of the construct in the office environment. Human Factors 25 (6), 701e711. Mandal, A.C., 1982a. The Seated Man. Private Edition 11. Mandal, A.C., 1982b. Correct height of school furniture. Human Factors 24, 257e269. Mandal, A.C., 1994. Influence of furniture height on posture and back pain. In: Lueder, R., Noro, K. (Eds.), Hard Facts About Soft Machines; The Ergonomics of Seating. Taylor and Francis Publishing, London and Philadelphia, pp. 173e179. Mauss, M., 1979. Sociology and Psychology Essays (Brewster, B., Trans.). Routledge & Keegan Paul, London. Cited in Gurr et al. (1998)above. Nao-i, N., Noro, K., Kawano, N., 2009. Analysis and improvement of a chair for microscopic surgeons. In: The 32nd Annual Meeting of the Japanese Society of Ophthalmic Surgeons 2009 (in Japanese). Noro, K., 2007. Za saikou. Journal of Society of Biomechanisms (SOBIM) Japan 31 (1) (in Japanese). Noro, K., 2009a. Developing seating designs that support traditional Japanese sitting postures. In: Schlick, C. (Ed.), Industrial Engineering and Ergonomics. Springer-Verlag, Berlin Heidelberg, pp. 609e620.
319
Noro, K., 2009b. An ergonomic evaluation of kitchen knife handles through pressure distribution measurement on surface contact areas. In: 55th Frühjahreskongress Gesellschaft für Arbeitswissenschaft eV. (GfA), pp. 629e632. Noro, K., Fujimaki, G., Kishi, S., 2005. A theory on pressure distribution and seat discomfort. In: Vink, P. (Ed.), Comfort and Design. CRC Press, pp. 33e39. Noro, K., Lueder, R., Yamada, S., Fujimaki, G., Oyama, H., Hashidate, Y., 2006. Revisiting sittingdcross-cultural aspects of seating. In: Proceedings of HFES 50th Annual Meeting, pp. 814e819. Pollintine, P., Przybyla, A.S., Dolan, P., Adams, M.A., 2004. Neural arch load-bearing in old and degenerated spines. Journal of Biomechanics 37, 197e204. Pynt, J., Higgs, J., 2010. A History of Seating 3000 BC to 2000 AD: Function Versus Aesthetics. Cambria Press, NY. Pynt, J., Higgs, J., Mackey, M., 2002. Historical perspective milestones in the evolution of lumbar spinal postural health in seating. Spine (Phila Pa 1976) 27 (19), 2180e2189. Rempel, D.M., Wang, P.-C., Janowitz, I., Harrison, R.J., Yu, F., Ritz, B.R., 2006. A randomized controlled trial evaluating the effect of two task chair designs on shoulder and neck pain among sewing operators. Human Factors and Ergonomics Society Annual Meeting Proceedings 50, 1323e1326. Rohlmann, A., Arntz, U., Graichen, F., Bergmann, G., 2001. Loads on an internal spinal fixation device during sitting. Journal of Biomechanics 34 (8), 989e993. Rohlmann, A., Bergmann, G., 2000. Sitting furniture has only a minor influence on back shape. European Spine Journal 9, 286. Schurr, M.O., Buess, G.F., 2000. Systems technology in the operating theatre: a prerequisite for the use of advanced devices in surgery. Minimally Invasive Therapy & Allied Technology 9 (3/4), 179e184. Schurr, M.O., Buess, G.F., Wieth, F., Saile, F.-J., Botsch, M., 1999. Ergonomic surgeon’s chair for use during minimally invasive surgery. Surgical Laparoscopy Endoscopy & Percutaneous Techniques 9 (4), 244e247. Shimode, M., 1992. Seating in connection with human body’s structure and function. In: Noro, K. (Ed.), Engineering for Life. The Open University Japan (in Japanese). Solomonow, M., Baratta, R.V., Zhou, B.H., Burger, E., Zieske, A., Gedalia, A., 2003. Muscular dysfunction elicited by creep of lumbar viscoelastic tissue. Journal of Electromyography and Kinesiology 13 (4), 381e396. Solomonow, M., 2009. Ligaments: a source of musculoskeletal disorders. Journal of Bodywork and Movement Therapies 13 (2), 136e154. Vink, P., Porcar-Seder, R., De, P., Lvaro, P., Krause, F., 2007. Office chairs are often not adjusted by end-users. Human Factors and Ergonomics Society Annual Meeting Proceedings 51, 1015e1019. Wallace III, R.B., February 1999. The 45-degree tilt: improvement in surgical ergonomics. Journal of Cataract & Refractive Surgery 25 (2), 174e176. Wilke, H.J., Neef, P., Caimi, M., Hoogland, T., Claes, L.E., 1999. New in vivo measurements of pressures in the intervertebral disc in daily life. Spine 24 (8), 755e762. Wu, C., Miyamoto, H., Noro, K., 1998. Research on pelvic angle variation when using a pelvic support. Ergonomics 41 (3), 317e327. Yu, Chi-Yuang, Keyserling, W.M., 1989. Evaluation of a new work seat for industrial sewing operations. Applied Ergonomics 20 (1), 17e25. Zacharkow, D., 1988. Posture: Sitting, Standing, Chair Design and Exercise. Charles C. Thomas Publishing, Illinois. Zhang, L., Helander, M.G., Drury, C.G., 1996. Identifying factors of comfort and discomfort in sitting. Human Factors: Journal of the Human Factors and Ergonomics Society 38 (3), 377e389.
Contents lists available at ScienceDirect
Applied Ergonomics journal homepage: www.elsevier.com/locate/apergo
Application of Zen sitting principles to microscopic surgery seating Kageyu Noro a, *, Tetsuya Naruse b, Rani Lueder c, Nobuhisa Nao-i d, Maki Kozawa d a
Waseda University/ErgoSeating Co., Ltd., Tokyo, Japan Gifu Pref. Research Institute for Human Life Technology, Takayama, Japan c Humanics ErgoSystems, Inc., Encino, CA, USA d Department of Ophthalmology, Faculty of Medicine, Miyazaki University, Miyazaki, Japan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 December 2009 Accepted 31 May 2011
This paper describes the application of an alternative seating concept for surgeons that reflects the research of Zen sitting postures, which require Zazen meditators to maintain fixed postures for long durations. The aim of this alternative approach is to provide sitters with a seat pan with sacral support1 that provides a more even distribution of seat pressures, induces forward pelvic rotation and improves lumbar, buttock and thigh support. This approach was applied to the development of a chair for microscopic surgery. The experimental chair is a seat pan that closely matches the three-dimensional contours of the user’s buttocks. Seat comfort was evaluated by comparing both changes in pelvic tilt and seat pressure distributions using Regionally-Differentiated Pressure Maps (RDPM) with subjective ratings of surgeons while operating in prototype and conventional chairs. Findings include that the sacral support of the prototype chair prevents backward pelvic rotation, as seen in zazen (Zen sitting postures). Preliminary data suggests that the prototype provided greater sitting comfort and support for constrained operating postures than did the conventional chair. These findings support the selective application of concave-shaped seat pans that conform to users’ buttocks and reflect Zen sitting principles. Ó 2011 Elsevier Ltd and The Ergonomics Society. All rights reserved.
Keywords: Seating design Surgical operations Pelvic tilt Sacral support Seat pan Concave chair Seat comfort Pelvis Seat pressure distributions Zen sitting Zazen meditation
1. Introduction 1.1. Western view of seat comfort Pynt et al. (2002) and Pynt and Higgs (2010) trace early attention to sitting postures to Ancient Egypt, pointing to the design of a forward tilting seat from 1500 BC. Even so, much innovation in Western seating has evolved from the findings of Keegan (1953, 1964), who reported that open thigh-torso angles more evenly
* Corresponding author. Tel./fax: þ81 3 3238 5239. E-mail address: [email protected] (K. Noro). 1 The term ‘sacral support’ seems to be commonly used in the U.S., while Japanese people customarily use ‘pelvic support’. The first known use of the term ‘pelvic support’ appeared in Yu and Keyserling (1989). Wu et al. (1998) performed an indepth analysis of the effectiveness of pelvic support for inducing pelvic tilt. In recent years, advances in technology have enabled the direct measurement of pressures on the sacral area that are distinct from those on the pelvic area. In this article, the term ‘sacral’ is used only when the sacral area is identified by palpation. The distinction between pelvic and sacral supports is defined in Section 6.2.1 of this article in relation to Fig. 10. 2 It might be pointed out that Keegan’s research, though brilliant and historically pivotal, would have been considered quite limited today as it represented repeated X-rays of a single young male lying on a horizontal surface.
distribute loads on the spine. Keegan2 focused on pathological problems caused by flexion of the lumbar spine associated with seated postures and proposed design criteria to promote lumbar lordosis. Mandal (1982a,b) expanded on Keegan’s findings and proposed forward tilting seat pans to induce lumbar lordosis. Congleton et al. (1985) espoused the adoption of more neutral forward and back sitting postures. A broad range of new and innovative designs expanded on these Western concepts of seating. Yet, despite the vast body of literature on the topic, we continue to struggle to define seat comfort. Corlett and Bishop (1976) shifted our focus from measuring comfort to discomfort because comfort is more difficult to measure and interpret and also because the two represent not one dimension but rather different constructs. Habsburg and Mittendorf (1980) concluded that subjects’ comfort ratings were based on something other than their own personal experience.3 Analyses by Zhang et al. (1996)
3 These authors found that raters judged seats more stringently in the personal suitability judgment (for me/not for me) than in their ratings on overall seat comfort, suggesting that their comfort judgment hinged upon the projected comfort of an independent and objective user.
0003-6870/$ e see front matter Ó 2011 Elsevier Ltd and The Ergonomics Society. All rights reserved. doi:10.1016/j.apergo.2011.06.006
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
and Helander and Zhang (1997) on the properties of comfort and discomfort led them to conclude that the two constructs measured different dimensions. Kuijt-Evers et al. (2005) proposed a unified field theory for comfort and discomfort. The process becomes even more complex when attempting to evaluate design solutions. Reviews by Lueder (1983) and Corlett (1989) emphasized the lack of objective measures for evaluating sitting comfort; on this basis, the latter suggested instead focusing on the specific context and functional requirements of a seat. In their review, De Looze et al. (2003) noted the dearth of commonly recognized measures and objective findings for sitting comfort. The research on sitting comfort demonstrates a particularly pronounced relationship between seat pressure and comfort. De Looze et al. (2003) concluded that the most consistent predictor of seat comfort related to seat pressure distribution4 and that this relationship was considerably more straightforward than with research measuring muscle activity or spinal profiles. Using a specially designed seat fixture, Goossens (1998) varied pressures and found a strong correlation between the amount of pressure applied to the buttocks and discomfort. Goossens et al. (2005) found subjects were quite sensitive to JND/Just Noticeable Differences in seat pressures at the ischial tuberosities. Compressive loads and displacement of force are affected by our age and the degeneration of the spine (e.g., Pollintine et al., 2004). Even so, Dolan and Adams (2001) noted, “tissue stress probably plays a major role in determining if a given tissue is painful, it is tissue stress rather than overall loading which influences the metabolism of connective tissue cells”. Although backrests may provide important benefits (s.f. Pynt and Higgs, 2010; Rohlmann et al., 2001, Wilke et al., 1999), some emphasized the particular importance of pelvic and sacral support. Grandjean (1973) pointed to the relative superiority of pelvic and sacral support to lumbar supports “since the prolonged maintenance of an upright seated posture with a lordosis of the lumbar spine results in strain on the extensor muscles of the back”. Zacharkow (1988) recommended the provision of pelvic supports just below the posterior pelvic rim in order to support the upper sacrum, pelvis and lumbar spine. Corlett (1999, 2006) emphasized the functional requirements of pelvic support of the buttocks and thighs. Others focused on promoting natural postures through the design of the seat pan. Research by Yu and Keyserling (1989) led to the development of a work chair for sewing with a contoured seat pan that tilted at the front to promote thigh, pelvic, lumbar and thoracicsupport. Rempel et al. (2006) found that garment workers provided with an adjustable height seat pan that tilted at the front experienced a greater improvement in neck/shoulder pain over a four-month period than the control group using an adjustable height flat seat pan. New and innovative designs such as Corlett’s and Gregg (1994) and Corlett’s (2006) Nottingham chair, Opsvik’s Balans chair (Lueder, 2010) and the Bambach Saddle Seat (Gale et al.,1989; see also Gadge and Innes, 2007) emphasized promoting neutral postures through the design of the seat pan. Wu et al. (1998) found that seat pans with pelvic support promoted forward pelvic tilt and induced a more neutral posture than did backrest lumbar supports. Rohlmann and Bergmann (2000) found a padded wedge improved back shape, though not implant loads. Even so, Rohlmann et al. (2001) concluded from their study of a group of patients that opportunities to move are more important than features of the chair.
4 De Looze et al. (2003) reviewed studies that compared seat comfort findings that matched physiological parameters with subjective measures of seat comfort.
309
1.2. Alternative Eastern perspectives of seating It is not surprising that Western assumptions about sitting and seating contrast markedly with traditional Eastern perspectives on sitting. Howes (1957) reviewed the cultural differences in postures and styles of sitting that are specific to gender and nations, particularly between the East and West. Mauss (1979) and Gurr et al. (1998) point to the limitations of Western concepts of posture and seating, which translate poorly to other cultures and may increase associated risk of musculoskeletal disorders. 1.2.1. What is Zen sitting? Noro (2009a,b) reviewed the concept of seat comfort as it applies to Zen sitting, an Eastern way of sitting.5 Noro (2007) surveyed Zen priests’ zazen postures, which reflect the principles of Zazen Buddhism and was developed by the great Master Dogen in the 13th century, who introduced the Zafu posture to promote postural stability. For this reason, Zen monks in Japan now commonly assume Zafu while meditating (Fig. 1) The Zafu sitting style is in marked contrast with those in the West. While Zafu sitting promotes postural stability, Western chair designs aim to facilitate changes of posture. Placing a Zafu underneath one’s buttocks facilitates deep breathing and lengthens the spine by inducing a forward pelvic tilt underneath the gluteus maximus around the sacrum (Fig. 1). In contrast, Western seats commonly attempt to induce pelvic tilt through lumbar supports. 1.2.2. Zen sitting and chairs Noro et al. (2006) contrasted this Eastern view with Western assumptions in seating, based on both medical findings and observations of users interacting with chairs. The implications of medical findings are addressed first. Adams and Hutton (1985) pointed to a lack of reliable evidence that upright sitting benefits the lumbar spine. These authors cited findings of Fahrni and Trueman (1965) from their radiographic experiments on lumbar spines and posited the superiority of kyphotic lumbar spines over postures with lumbar lordosis. They based their opinion on evidence that lumbar disc degeneration is rare among people who habitually sit or squat in postures that flex (flatten) the lumbar spine. In his review, Deyo (1998) reported that numerous studies demonstrate the high prevalence of disk bulges or herniation among asymptomatic people.6 Some findings point to alternate perspectives in chair design. Shimode (1992) noted that the forward inclination of lumbar vertebra is necessary for standing but not sitting. Mandal (1982a,b,1994) suggested that lumbar supports function only when backrests recline. Corlett and Eklund (1984) suggested backrests only promote desirable lumbar curvatures when users lean back; once the flattening occurs during work, “the curve will
5 Zen sitting is only one of many Eastern sitting postures cited by Howes (1957). The lotus position is a particularly important Zazen posture, which Buddha first introduced circa 500 BC. The lotus sitting style differs from traditional Yoga sitting postures and is characterized by symmetrical positioning of the left foot over the right thigh and the right foot over the left thigh. As Buddhism spread from India across the East, the influence of the lotus sitting style expanded across Asia. 6 As one example, Deyo described a “1990 study by Scott D. Boden of the George Washington University Medical Center and his colleagues looked at 67 individuals who said they had never had any back pain or sciatica .MRI found them in onefifth of pain-free study subjects under age 60. Half of that group had a bulging disk, a less severe condition also often blamed for pain. Of adults older than 60, more than third have a herniated disk visible with MRI, nearly 80 percent have a bulging disk, and nearly everyone shows some age-related disk degeneration”.
310
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
Fig. 1. Top row, a Zen Buddhist priest assumes traditional Zazen posture while sitting on a Zafu cushion at the Zennoji Temple in Takayama, Japan. When sitting on zafus, the arrangement between the lower knees and higher buttock positions provide concave postural support that induces forward pelvic tilt. Bottom row, a line of Zen Buddhist priests practicing zazen at a Zazen training hall. Each zafu is occupied by its possessing priest as the primary user.
not push back in”,7 although they did not focus on lumbar support, this general principle appears to be supported by Solomonow et al. (2003) and Solomonow (2009). Using pig cadavers, Brodeur and Reynolds (1990) concluded that lumbar supports have little effect on the contours of the lumbar spine. Rather, they found that the pelvic tilt exerts a primary influence on lumbar curvature. It also tilts the angle of the individual vertebra so that pressures at the front of the discs increase (Adams et al., 1996; Bendix et al., 1996; Corlett, 1999). This conclusion is not fully agreed on. For example, Andersson et al. (1974, 1975) found that in a carefully controlled laboratory environment that lumbar supports reduce loads on the spine. Bendix et al. (1996) reported that lumbar supports on backrests helped reinstate lumbar curves while performing tasks, but not during passive sitting and reading. Another consideration is the use of the backrest. Dowell et al. (2001) found that the majority of workers work with their back
7
Rather, Corlett and Eklund (1984) and Corlett and Gregg (1994) emphasized the central importance of the lumbar support for “transmitting some of the weight of the trunk, head and arms through the chair structure, rather than through the lumbar spine”. Corlett (personal communication 2010) emphasized that the Nottingham seat induces forward pelvic tilt by both its seat pan profile and higher sitting position.
unsupported for most of their work day, although the rates vary with the task. Vink et al. (2007) and a review by Lueder (1994) suggested that users rarely adjust their backrest. Noro et al. (2006) suggested that we rethink prevailing assumptions regarding the centrality of backrests in chair design and develop a theory of seating and sitting that is independent of musculoskeletal systems.
1.3. Eastern approach exemplified by Zen sitting and its supportive evidence Fig. 1 portrays a priest assuming zazen posture while sitting on a traditional zafu cushion from three perspectives. Side view (B) shows the forward sacral/buttocks tilt when seated on the zafu cushion (A). Zazen postures are underpinned by the following characteristics: 1) The sacral support prevents backward pelvic rotation; 2) Increased surface contact support of the buttocks on the seat pan; 3) Reduced pressure between the buttocks and the seat pan, resulting from this increased surface contact; 4) Knees positioned below the buttocks; and
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
5) Zafus customized to fit the dimensions of the individual, particularly the 3D shape of the buttocks and length of the leg. The fifth characteristic in the list above was inherited from the 13th century. Accordingly, each zafu implies the existence of a primary user. Yet only zazen professionals are able to customize zafus to the user’s buttock shape. The lower half of Fig. 2 demonstrates a relationship between the contour appearing in Fig. 1 and the sacral area. Zabutons are commercial versions of zafu, which have been used for some time, which tend to rotate users’ pelvic girdles back (Noro, 2009a,b). A pelvic-support zabuton was developed to overcome this limitation. The upper right of Fig. 2 depicts a commercially available zabuton that provides pelvic support and promotes the first four out of the five previously mentioned features of zazen posture. Conventional and pelvic-support zabutons were experimentally compared. Table 1 compares pelvic tilt angles measured during experimental trials when 44 subjects sat on both pelvic-support and conventional zabutons. Subjects (25 males and 29 females aged between 20 and 71) were instructed to assume a recommended sitting posture with their pelvis rotated forward. Instructions to subjects sitting on the pelvic-support zabuton were associated with an average of 12.5 pelvic tilt, a marked improvement from an average 22 tilt when subjects receiving the same instruction sat on a conventional zabuton. Even so, there was considerable variability in pelvic tilt between individuals that appeared to relate to difference in their physical size. These findings suggest that the pelvic-support zabuton consistently improved the pelvic tilt toward that of the standing position. This beneficial pelvic rotation was evident with both Zen Buddhist priests and subjects from the general population, and can be attributed to both the greater amount of support for the knees and
311
Table 1 Average pelvic tilt measurements in degrees associated with sitting in pelvicsupport and conventional zabutons. Item
Average (median values) Standard error Standard deviation Variance Range Min Max Number F test T test(two-sided)
Pelvic tilt angles (median values in deg.) Pelvic-support zabutons
Conventional zabutons
12.5 1.1 7.2 52.1 27.7 29.8 2.2 44 F(43,43) ¼ 0.47, p < 0.05 T(76) ¼ 4.99, p < 0.05
22.0 1.6 10.5 109.8 45.0 50.9 5.8 44
buttocks and the different elevation between buttocks and both knees (see Fig. 1, side view).
2. Characteristics of microsurgery 2.1. Considerations for microscopic surgery operations Schurr and Buess (2000), Wallace (1999) and Nao-i et al. (2009) associated the surgeon’s increased risk of musculoskeletal disorders with the following characteristics of surgical work: 1. 2. 3. 4. 5.
Sustained foot elevation while operating surgical equipment; Seat pans impact surgeons’ thighs; Inadequate hand support during surgery; An inability to recline or sustain pelvic support; Sustained neck flexion while using microscopes; and,
Fig. 2. A zafu (left) and pelvic-support zabuton (top right), each placed on conventional zabutons in the Zen training hall at Sokoji Temple in San Francisco. A model of buttocks is shown in the lower right area. The circled section points to the sacral area.
312
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
6. Long-term constrained postures. Such restrictive postural demands contribute to the development of acute disorders (Schurr and Buess, 2000; Wallace, 1999). Fig. 3 depicts a surgeon performing eye surgery while using a microscope (circle 5). The surgeon’s seat provides considerably less support of the buttocks than is commonly found in conventional seating. These seats enable surgeons to assume perch-style postures with legs extended (circle 1). The surgeon lacks hand support while operating (circle 3). 2.2. Optimal characteristics of seating for surgeons Schurr et al. (1999) and Schurr and Buess (2000) suggested that surgeons a) assume semi-standing positions to facilitate reach, b) sit on horn-shaped seating that prevents sliding forward and c) use user-friendly foot-pedals. Wallace (1999) suggested tilting the microscope forward a few degrees and the patient’s head forward 45 . Congleton et al. (1985) espoused the adoption of neutral postures to reduce fatigue during surgery. Such suggestions were based on the theories of Mandal (1982a,b), who proposed that seat pans tilt forward to promote lumbar lordosis by opening the thightorso angle per Keegan (1953, 1964) and Mandal (1982a,b). 3. Application of the Zazen concept to the design of surgical chairs It was hypothesized that the application of the theoretical basis for Zen postures would help mitigate postural restrictions associated with microsurgical operations. The characteristics of Zen postures (see Section 1.3) translate into the following design principles.
The different body parts are not equally able to withstand equivalent pressures acting on the tissues. Kishi (2005) reported a negative correlation between the amount of buttock deformation caused by sitting and seating comfort. Further, there was no correlation between the amount of deformation of the thighs and seating comfort. These findings suggest that the optimum pressure distribution may be achieved by introducing different or composite materials and shapes to the seat pan, that adapt the amount of support transmitted to the different buttock and thigh areas. 3.1.2. Second Principle: Adapt peak pressures that result as the sitter interacts with the seat pan in three separate ways (a) Gluteus maximus: The Gluteus Maximus is a major buttock muscle that extends from the end of the thigh muscle toward the lumbar via the ischial tuberosities. This muscle transmits information on seating comfort through its various sensory receptors. Congleton et al. (1985) wrote that buttocks pressures commonly range between 0 and 66.195 mmHg8 and must not exceed 66.2 mmHg. Noro et al. (2005) defined the “sitting comfort zone” as buttock pressures within 50 mmHg, which approximates that of Congleton et al. (1985). (b) Ischial tuberosities: When sitting, the ischial tuberosities interact with the apex of gluteus maximus. Seated pressure distribution measurements are consistently high in this area, located just beneath the torso. (c) Femoral region: In contrast to the buttock muscles, the femoral muscles cannot sustain heavy loads. Unlike the gluteus maximus, these muscles lack sensory receptors yet are sensitive to the sensation of discomfort and materials. The forward bending of the anterior edge of the seat pan (s.f., Yu and Keyserling, 1989) provides a reasonable accommodation.
3.1. Chair design principles 3.1.1. First Principle: Maximize the sitters’ seat pan contact area Larger surface contact areas provide a more even distribution of seat pressures over the pelvic girdle, resulting in a lower force per unit area.
3.1.3. Third Principle: Design the seat pan to emulate the 3-dimensional shape of the user’s buttocks Chair seat pans and backrests often function independently. In contrast, the Eastern perspective of the chair views this support as a “shell” that considers the seat and back in conjunction. Closely related to this perspective is the concept that the surgery chair ‘shell’ should emulate the 3D shape of the specific user surgeon’s buttocks as they assume their working postures. In addition, the angle between the shell and floor should reflect the Zen sitting principle that the knees be lower than the buttocks. 3.1.4. Fourth Principle: Adapt the floor-sitting tools to the primary users Since the 13th century, Zen sitting has traditionally dictated that floor-sitting tools (zafu or zabuton) are optimized to each user’s physical characteristics. This approach is particularly typical when achieving what we would now consider ergonomic objectives of this approach.
4. Development process 4.1. Formation of a research project team The prototype chair was not developed by a manufacturer but rather through a participatory approach with a team comprising ergonomists, surgeons, a specialist in cushioning, a clinical
Fig. 3. Ophthalmic surgery while using a microscope.
8 To maintain consistency, mmHg values are converted here from the original text of 0e1.28 psi from the original author (Congleton et al., 1985)
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
313
technologist and specialists in subjective evaluation. An ergonomist served as the team leader. Table 2 lists project development stages. 4.2. Production of prototype chair Table 2 lists the steps followed to develop a prototype chair. In creating the prototype, 3D contours of buttocks, sacral area and thighs of the primary user were measured during surgery. A detailed description of this stage is beyond the scope of this paper. Fig. 4 compares the prototype model created in Phase 2 of Table 2 with a conventional chair. The prototype chair (A) features a shell that emulates the 3D shape of the primary user’s buttocks. Its concave-shaped shell was cushioned and covered with a surface material. The curved lines represent typical contours. In contrast, the conventional chair (B) provides a convex seat pan. Though it resembles a stool, for the purposes of this paper it was named a chair so as to comply with the official designation used in ophthalmic surgery. 5. Experiments Experiments were composed of a trial session and ensuing fullfledged experiments. The trial session was conducted by Sub. A, the surgeon who oversees the operation room, who permitted the use of the surgical prototype chair. For the full-fledged experiments, all subjective and objective measurements were performed in the operation room. 5.1. Subjects Eleven subjects (7 males and 4 females) served as experimental participants. Among these, subjects A through D were surgeons (Sub. D only participated in some objective measurements). Subjects E through K were assistant doctors. Percentile values for subject statures ranged from 14.7 to 84.2 (females) and 11 to 84.4 (males) (Kouchi et al., 2000). Measurements were carried out during ten surgical operations.
Table 2 Stages of project development. Phase 1: Preliminary study and formation of Project team Initial review of Zen sitting theories and its supportive evidence Considerations for Microscopic surgery operations Characteristics of microsurgical work Application of the Zazen concept to surgical chair design Form Project team Phase 2: Creation of 3D prototype chair and experiments Creat 3D prototype chair Trial session by primary user to examine feasibility of prototype chair for use in operating room Perform trial session by primary user (Sub A) Experiments Subjective measurements 1 Evaluation of the relative comfort 2 Body parts discomfort 3 Paired comparison of two chairs Objective measurements 1 Pelvic tilt 2 Body pressure Phase 3: Analysis of findings and future work Result of subjective ratings Result of objective data Feasibility evaluation for commercial versions Proposal of a physiological model for seat comfort
Fig. 4. The concave-shaped prototype (A), conventional chair with a convex seat pan (B), and corresponding sitting postures assumed by the surgeon (Sub. A).
5.2. Subjective evaluations Thirteen questionnaires on a 5-point scale were given to subjects asking their sense of comfort as they got seated to compare two types of model, prototype and conventional. Surgeons and assistant doctors served as the subjects. Surgeons were asked about their impressions felt on their body parts, sacral, ischial, and thigh areas, prior to and following surgery. Lastly, surgeons and assistant doctors were requested to compare the prototype and conventional chairs to determine which was better. ANOVA was used to analyze rating. For all figures in this paper, responses are digitized as follows: Definitely not ¼ 2 Somewhat not ¼ 1 Neutral ¼ 0
Somewhat yes ¼ 1 Definitely yes ¼ 2
5.2.1. Objective measurements 5.2.1.1. Pelvic tilt. Fig. 5 depicts the experimental device used to measure pelvic tilt. Pelvic tilt was measured using a patented gyroscope9 that measures 3D pelvic rotation with pitch and roll ranging between 60 and þ60 , respectively (Wu et al., 1998). In
9 Japan Patent Office Certificate (2007): Title of invention, a pelvic-angle measuring device; Inventor, Kageyu Noro; Patent no. 3928103 2004.
314
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
Fig. 5. Measurement of pelvic tilt in the operation room; A: The dashed arrow denotes negative pelvic tilt; B: Experimental Gyroscope; C: Device mounted under surgical gowns.
Fig. 6. Experiment using a pressure-imaging pad; 1: Sensor; 2: Sensor placed on chair; 3: Surgeon seated; 4: Measurement of pressure distribution.
this paper, pitch angles relevant to forward pelvic tilt are assumed to take positive values.10 5.2.1.2. Body pressure distributions. Fig. 6 demonstrates the experimental use of a pressure-imaging pad. A polyester pressureimaging square-type pressure measurement pad 45 cm in side length was embedded with 36 36 cells. It measured a sampling rate of 10 frames/s with pressure ranging from 0 to 220 mmHg. Accuracy of measurement was approximately 10% (10 mmHg).
10 The terms tilt and rotation represent different expressions of the same phenomenon in pelvic movements. While positive and negative indicators of crossdirectional tilt or rotation are arbitrary, we established baselines for anterior tilt or rotation as described by Wu et al. (1998).
Calibrations were conducted as appropriate. A clinical technologist identified the locations of surgeons’ buttocks, thighs and sacrum through direct palpation.
6. Results of experiments 6.1. Result of subjective ratings A trial session to examine the experimental chairs and protocols (including subjective and objective measurements) was conducted by primary user Sub. A as he worked at the clinic. The subject rated the prototype as superior to the conventional chair. The following is the result of subjective ratings taken about one year after the trial session.
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
Fig. 7. Ratings of body part discomfort at the sacrum, ischial tuberosities and thighs.
315
The primary user Sub. A rated all body part discomfort scores as 2 points while sitting in the prototype chair for both before and after the operations (See Fig. 7). On the contrary, the scores given by the other subjects increased to 2 points for each body area after the prototype chair was used, 1 point above the 1 point rating prior to its use. The reason is that before the use of the chair, the evaluations were conducted with the positional relationship between surgeons and the surgical table remaining rough and the evaluations after its use reflected the fact that the positional relationship became exact in the course of surgical operations. This reason was revealed by surgeons’ subsequent comments. The primary user (Sub. A) rated the slide-resistance of the prototype chair 2 points, compared with other subjects’ average ratings of 0.5 point. The distance between Sub. A’s feet and foot switches was optimal. In contrast, other subjects noted that the gap between the foot switches caused them to slide forward. Paired comparisons associated with the two chairs are summarized in Fig. 8; the prototype was strongly preferred to the conventional chair. 6.2. Analysis of objective data
Fig. 8. Paired comparisons: Surgeons and assistant doctors were requested to compare two types of chairs to determine which was better.
Fig. 7 depicts subjective body part discomfort ratings for the sacrum, ischial tuberosities and thighs associated with the use of the prototype chair. The surveys included questions about the slideresistance of the chairs while operating.
6.2.1. Static measurement 6.2.1.1. Preliminary trial test. Fig. 9 summarizes objective measurements conducted during a preliminary trial session that lasted 50 min with primary user Sub. A. 6.2.1.2. Experimental testing. Objective measurements were performed approximately one year after the initial testing. The evaluation of the contact surface between a surgeon and the prototype chair was conducted by measuring the subjects’ pressure distribution during work prior to surgical operation. Fig. 10 compares body pressure distributions between the prototype and conventional chairs.
Fig. 9. Basic statistical data associated with contact pressures. A measuring instrument used is different from that for most charts shown in Fig. 10.
316
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
Fig. 10. Pressure distribution measurements of three surgeons performing surgery while seated on the prototype and conventional chairs.
Fig. 10 depicts the six areas with rectangles that identify the surgeon’s buttocks, thighs and sacrum through palpation by a clinical technologist. This approach measures the Regional Differentiation of Pressure Distributions associated with the “Regionally-Differentiated Pressure Maps” (RDPM) (Noro, 2009a). The pressure maps and table in the figure both represent stable “moment to moment” values during surgery. Fig. 10 points to clear differences between two types of chairs in the size of pressure distribution, peak pressures and their associated locations. These distinctions are presumed to be associated with the differences between the concave-shaped prototype and a conventional chair with a convex seat pan. Note that some cells inside the Fig. 10 tables are left blank, as the conventional chair lacks sacral and lateral support. Area A in Fig. 10 represents sacral support, while pelvic support corresponds to the entire areas except for the thigh area. 6.2.2. Changes in pelvic tilt Pelvic tilt was measured as Sub. A performed vitreous surgery while seated on the prototype chair. Fig. 11 depicts changes of pelvic tilt throughout the surgery.
Fig. 11 suggests that, following surgical preparation, the surgeon assumes a fixed posture for approximately 590 s while operating. The subject maintains a nearly constant pelvic tilt (about 10 backward tilt relative to the arbitrarily defined 0 reference point while standing). Postures often exceed 20 backward pelvic tilt.
Fig. 11. Changes in pelvic tilt during a session of vitreous surgery that lasted 1 h and 3 min from 9:11 to 10:14 taken from Sub. A (seat height: 44.5 cm) using the prototype chair. Steps A through E include the following: A: start of the vitreous surgery, intraocular procedures. BeC: preparation of the vitrectomy machine, procedures outside of the eye. C: re-start of the vitreous surgery. D: end of the vitreous surgery, scleral wound closure (outside of the eye). E: end of the surgery.
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
317
Table 3 Summary of objective data.
These correspond to surgeon’s look-back actions at the instrument table. It is also possible that some measurements might inadvertently measure the surgeon at rest. Noro (2009a,b) demonstrated that pelvic tilt for conventional chairs often exceed 19 . This suggests that, as with zazen, the sacral support is effective at preventing backward pelvic rotation.
the prototype chair was rated more comfortable than the conventional chair, with further increases in comfort ratings after surgery (See Fig. 8).
6.2.3. Summary of objective data Table 3 summarizes the objective experimental data collected during ten surgeries, as well as the surgeons, chairs used, and averaged values for duration, pelvic tilt, mean pressures and contact areas during the experimental sessions. Differences in pelvic tilt between prototype and conventional chairs were not significant (see Table 3). Pelvic tilt measurements of some subjects who sat on the prototype chair approached zero relative to the standing posture, while others such as 15.8 (Sub. A) and 18.4 (Sub. D) are comparable to the 19 pelvic tilts associated with sitting on a folding chair (Section 1.2.2). This finding suggests that further investigation is needed to evaluate the potential for subsequent versions of the prototype chair to consistently promote better sitting postures. Further, the size of the body support area of the prototype chair ranges between 1318 cm2 for Sub. A and 868 cm2 for Sub. D,11 are significantly greater than that when the conventional chair was used12 (702 cm2 for Sub. B and 558 cm2 for Sub. C) for the same kind of surgery and at the same surgical table. Given this, the objective data are consistent with the subjective data. This difference in body size support area and also in peak seated pressure values were statistically significant. With the exception of pelvic tilt data, the objective data consistently reflected subjective findings;
7.1. Verification of the hypothesis
11 12
Measured during surgery sessions 6 and 8. Measured during surgical sessions 9 and 10.
7. Discussion
This paper described the development of a special purpose chair that aimed to mitigate the physical loads associated with surgeon’s work in fix postures required during microscopic surgery operations (described in Section 2.1). Its development was based on traditional concepts adopted for Zen sitting. That is, the experimental hypothesis reflected criteria 1) through 5) in Section 1.3. The application of this concept emphasized both the maximization of contact area of a seat and the modification of peak pressure values around the gluteus maximus, ischial tuberosities and femoral regions. The prototype chair greatly increased the extent of the sitter’s contact area of support (
318
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319
pressure distributions acting on muscle sites that were identified through palpation by a clinical technologist and defined as the boundaries of Regionally-Differentiated Pressure Maps (RDPM). The RDPM provides a more detailed analysis of pressures imposed on human bodies than has previously been demonstrated in past studies by Congleton et al. (1985) and Noro et al. (2005). As shown in Fig. 10, seated pressure distributions on the femoral regions of D-L and D-R for the prototype chair are considerably lower than those of the conventional chair. Findings of Schurr and Buess (2000), Wallace (1999) and Nao-i et al. (2009) suggest that the implementation of characteristics of zazen postures, particularly the criteria 4 “sufficiently low buttock contact pressure” (Section 1.3), might theoretically mitigate some extent of risk of incurring musculoskeletal disorders. Even so, as shown in Fig. 10, measured pressure distributions of Area B of the prototype were higher than expected. This concern might possibly be circumvented through further changes in cushioning materials at this area to enhance seating comfort. The findings in this paper also emphasize the importance of concave surface that support the buttocks and sacrum for comfort. Schurr et al. (1999) and Schurr and Buess (2000) suggested that the ideal surgery chair would enable a surgeon to assume semi-standing positions that facilitate reach and foot-pedal operations while sitting on a horn-shaped seat that prevents forward sliding actions. The Zen-based approach reflects these recommendations by Schurr and Buess (2000).
7.2. Primary user approach Traditionally, ergonomics specialists commonly establish adjustment ranges by identifying percentile values of relevant anthropometric dimensions of the user population. Although this approach sometimes leads to design solutions that are less than optimal for certain individual users, it aims to serve as a best overall compromise for the general population of users. Naturally, this research does not suggest that such approaches are inappropriate for
Fig. 12. A physiological model for seat comfort.
conventional purposes and general use. The primary user approach aims to optimize designs for selected individuals whose work requires further tailoring. Noro (2009a,b) previously addressed considerations associated with mass production of concave-shaped seating. 7.3. A physiological model for seat comfort Fig. 12 depicts a seat comfort model that reflects the design theory described in this article. The intent of this model is to suggest an alternative approach that incorporates physiological and objective data for evaluating seat comfort. In particular, the sensory nerves shown in the buttock and thigh regions A and B, respectively, in Fig. 12 are associated with initial sensations of comfort or discomfort which are subsequently verbalized after processing by the central nerve system. This model is proposed as an alternative physiological model for seat comfort. Acknowledgments The authors thank Shinichi Watanabe at Sanko Urethane Co., Ltd. and Masato Kakudo at Hachido Co., Ltd., and Kazutoshi Takagi at Takagi Seiko Co., Ltd. for their generous sponsorship and manufacture of the prototype chairs. They are indebted to Shunji Yamada at ErgoSeating Co., Ltd. for his invaluable participation, as well as for the invaluable insight and comments by Jenny Pynt at Charles Sturt University. Finally, the author Kageyu Noro thanks M.C. Mandal for his contributions to the field of ergonomics, and for his personal guidance over 25 years ago. References Adams, M.A., Hutton, W.C., 1985. The effect of posture on the lumbar spine. Journal of Bone and Joint Surgery 67-B (4), 625e629. Adams, M.A., McMillan, D.W., Green, T.P., Dolan, P., 1996. Sustained loading generates stress concentrations in lumbar intervertebral discs. Spine 21 (4), 434e438. Andersson, B.J., Ortengren, R., Nachemson, A.L., Elfstrom, G., Broman, H., 1975. The sitting posture: an electromyographic and discometric study. Orthopedic Clinics of North America 6 (1), 105e120. Andersson, B.J.G., Ortengren, R., Nachemson, A., Elfstrom, G., 1974. Lumbar disc pressure and myoelectric back muscle activity during sitting. Scandinavian J Rehabilitation Medicine 6, 104e114. Bendix, T., Poulsen, V., Klausen, K., Jensen, C.V., 1996. What does a backrest actually do to the lumbar spine? Ergonomics 39 (4), 533e542. Brodeur, R.R., Reynolds, H.M., 1990. Passive mechanics of the lumbo-pelvic spine for erect and slumped seated postures. In: Proceedings of the May 1990 International Conference on Spinal Manipulation. FCER, Arlington, Virginia, pp. 190e193. Congleton, J.J., Ayoub, M.M., Smith, J.L., 1985. The design and evaluation of the neutral posture chair for surgeons. Human Factors 27 (5), 589e600. Corlett, E.N., Eklund, J.A., 1984. How does a backrest work? Applied Ergonomics 15 (2), 111e114. Corlett, E.N., 1989. The Ergonomics Society. The Society’s lecture 1989. Aspects of the evaluation of industrial seating. Ergonomics 32 (3), 257e269. Corlett, E.N., 2006. Background to sitting at work: research-based requirements for the design of work seats. Ergonomics 49 (14, 15), 1538e1546. Corlett, E.N., 1999. Are you sitting comfortably? International Journal of Industrial Ergonomics 24 (1), 7e12. Corlett, E.N., Bishop, R.P., 1976. A technique for assessing postural discomfort. Ergonomics 19 (2), 175e182. Corlett, E.N., Gregg, H., 1994. Seating and access to work. In: Lueder, R., Noro, K. (Eds.), Hard Facts About Soft Machines; The Ergonomics of Seating. Taylor and Francis Publishing, London and Philadelphia, pp. 335e345. De Looze, M.P., Kuijt-Evers, L.F., Van Dieen, J., 2003. Sitting comfort and discomfort and the relationships with objective measures. Ergonomics 46 (10), 985e997. Deyo, R.A., August 1998. Low-back pain. Scientific American (Japanese version). Nikkei Science 279, 46e53. Dolan, P., Adams, M.A., 2001. Recent advances in lumbar spinal mechanics and their significance for modeling. Clinical Biomechanics 1, S8eS16. Dowell, W.R., Yuan, F., Green, B.H., 2001. Office seating behaviors: an investigation of posture, task, and job type. Human Factors and Ergonomics Society Annual Meeting Proceedings 45, 1245e1248. Fahrni, W.H., Trueman, G.E., 1965. Comparative radiological study of the spines of a primitive population with North Americans and Northern Europeans. Journal of Bone and Joint Surgery [British Volume] 47B (3), 552e555.
K. Noro et al. / Applied Ergonomics 43 (2012) 308e319 Gadge, K., Innes, E., 2007. An investigation into the immediate effects on comfort, productivity and posture of the Bambach saddle seat and a standard office chair. Work 29 (3), 189e203. Gale, M., Feather, S., Jensen, S., Coster, G., 1989. Study of a workseat designed to preserve lumbar lordosis. Australian Occupational Therapy Journal 36, 92e99. Goossens, R.H.M., 1998. Measuring factors of discomfort in office chairs. In: Scott, P.A., Bridger, R.S., Charteris, J. (Eds.), Global Ergonomics, vol. 2. Elsevier, Amsterdam, pp. 371e374. Goossens, R.H., Teeuw, R., Snijders, C.J., 2005. Sensitivity for pressure difference on the ischial tuberosity. Ergonomics 48 (7), 895e902. Grandjean, E., 1973. The Physiological design of household furniture (Chapter 4). In: Ergonomics of the Home. Taylor & Francis, Ltd., London, pp. 95e135. Chapter 4. Gurr, K., Straker, L., Moore, P., 1998. Cultural hazards in the transfer of ergonomics technology. International Journal of Industrial Ergonomics 22 (4e5), 397e404. Habsburg, S., Mittendorf, L., 1980. Calibrating comfort: systematic studies of human responses to seating. In: Oborne, D.J., Levis, T.A. (Eds.), Human Factors in Transport Research. Academic Press, New York. Helander, M.G., Zhang, L., 1997. Field studies of comfort and discomfort in sitting. Ergonomics 40 (9), 895e915. Howes, G., 1957. The anthropology of posture. Scientific American 196, 123e132. Keegan, J.J., 1953. Alterations of the lumbar curve. Journal of Bone and Joint Surgery 35, 589e603. Keegan, J.J., 1964. The medical problem of lumbar spine flatting in automobile seats. In: Booklet 838A 1e12. Society of Automotive Engineering. Kishi, S., 2005. Evaluation of sitting comfort based on hysteresis characteristics of human body and cushion. In: Master’s Thesis Waseda University, pp. 39e40. Kouchi, M., Mochimaru, M., Iwasawa, H., Mitani, S., 2000. Anthropometric Database for Japanese Population 1997e98. Japanese Industrial Standards Center (AIST, MITI). Kuijt-Evers, L., De Looze, M., Vink, P., 2005. Theory of comfort. In: Vink, P. (Ed.), Comfort and Design. CRC Press, pp. 13e32. Lueder, R., 1994. Adjustability in context. In: Lueder, R., Noro, K. (Eds.), Hard Facts About Soft Machines; The Ergonomics of Seating. Taylor and Francis Publishing, London and Philadelphia, pp. 25e35. Lueder, R., 2010. Ergonomics review of the literature relevant to Balans seating. Sponsored by VarierUSA.com. Downloaded 9/15/2010 at. www.humanics-es. com/ergonomics.htm#sitting. Lueder, R.K., 1983. Seat comfort: a review of the construct in the office environment. Human Factors 25 (6), 701e711. Mandal, A.C., 1982a. The Seated Man. Private Edition 11. Mandal, A.C., 1982b. Correct height of school furniture. Human Factors 24, 257e269. Mandal, A.C., 1994. Influence of furniture height on posture and back pain. In: Lueder, R., Noro, K. (Eds.), Hard Facts About Soft Machines; The Ergonomics of Seating. Taylor and Francis Publishing, London and Philadelphia, pp. 173e179. Mauss, M., 1979. Sociology and Psychology Essays (Brewster, B., Trans.). Routledge & Keegan Paul, London. Cited in Gurr et al. (1998)above. Nao-i, N., Noro, K., Kawano, N., 2009. Analysis and improvement of a chair for microscopic surgeons. In: The 32nd Annual Meeting of the Japanese Society of Ophthalmic Surgeons 2009 (in Japanese). Noro, K., 2007. Za saikou. Journal of Society of Biomechanisms (SOBIM) Japan 31 (1) (in Japanese). Noro, K., 2009a. Developing seating designs that support traditional Japanese sitting postures. In: Schlick, C. (Ed.), Industrial Engineering and Ergonomics. Springer-Verlag, Berlin Heidelberg, pp. 609e620.
319
Noro, K., 2009b. An ergonomic evaluation of kitchen knife handles through pressure distribution measurement on surface contact areas. In: 55th Frühjahreskongress Gesellschaft für Arbeitswissenschaft eV. (GfA), pp. 629e632. Noro, K., Fujimaki, G., Kishi, S., 2005. A theory on pressure distribution and seat discomfort. In: Vink, P. (Ed.), Comfort and Design. CRC Press, pp. 33e39. Noro, K., Lueder, R., Yamada, S., Fujimaki, G., Oyama, H., Hashidate, Y., 2006. Revisiting sittingdcross-cultural aspects of seating. In: Proceedings of HFES 50th Annual Meeting, pp. 814e819. Pollintine, P., Przybyla, A.S., Dolan, P., Adams, M.A., 2004. Neural arch load-bearing in old and degenerated spines. Journal of Biomechanics 37, 197e204. Pynt, J., Higgs, J., 2010. A History of Seating 3000 BC to 2000 AD: Function Versus Aesthetics. Cambria Press, NY. Pynt, J., Higgs, J., Mackey, M., 2002. Historical perspective milestones in the evolution of lumbar spinal postural health in seating. Spine (Phila Pa 1976) 27 (19), 2180e2189. Rempel, D.M., Wang, P.-C., Janowitz, I., Harrison, R.J., Yu, F., Ritz, B.R., 2006. A randomized controlled trial evaluating the effect of two task chair designs on shoulder and neck pain among sewing operators. Human Factors and Ergonomics Society Annual Meeting Proceedings 50, 1323e1326. Rohlmann, A., Arntz, U., Graichen, F., Bergmann, G., 2001. Loads on an internal spinal fixation device during sitting. Journal of Biomechanics 34 (8), 989e993. Rohlmann, A., Bergmann, G., 2000. Sitting furniture has only a minor influence on back shape. European Spine Journal 9, 286. Schurr, M.O., Buess, G.F., 2000. Systems technology in the operating theatre: a prerequisite for the use of advanced devices in surgery. Minimally Invasive Therapy & Allied Technology 9 (3/4), 179e184. Schurr, M.O., Buess, G.F., Wieth, F., Saile, F.-J., Botsch, M., 1999. Ergonomic surgeon’s chair for use during minimally invasive surgery. Surgical Laparoscopy Endoscopy & Percutaneous Techniques 9 (4), 244e247. Shimode, M., 1992. Seating in connection with human body’s structure and function. In: Noro, K. (Ed.), Engineering for Life. The Open University Japan (in Japanese). Solomonow, M., Baratta, R.V., Zhou, B.H., Burger, E., Zieske, A., Gedalia, A., 2003. Muscular dysfunction elicited by creep of lumbar viscoelastic tissue. Journal of Electromyography and Kinesiology 13 (4), 381e396. Solomonow, M., 2009. Ligaments: a source of musculoskeletal disorders. Journal of Bodywork and Movement Therapies 13 (2), 136e154. Vink, P., Porcar-Seder, R., De, P., Lvaro, P., Krause, F., 2007. Office chairs are often not adjusted by end-users. Human Factors and Ergonomics Society Annual Meeting Proceedings 51, 1015e1019. Wallace III, R.B., February 1999. The 45-degree tilt: improvement in surgical ergonomics. Journal of Cataract & Refractive Surgery 25 (2), 174e176. Wilke, H.J., Neef, P., Caimi, M., Hoogland, T., Claes, L.E., 1999. New in vivo measurements of pressures in the intervertebral disc in daily life. Spine 24 (8), 755e762. Wu, C., Miyamoto, H., Noro, K., 1998. Research on pelvic angle variation when using a pelvic support. Ergonomics 41 (3), 317e327. Yu, Chi-Yuang, Keyserling, W.M., 1989. Evaluation of a new work seat for industrial sewing operations. Applied Ergonomics 20 (1), 17e25. Zacharkow, D., 1988. Posture: Sitting, Standing, Chair Design and Exercise. Charles C. Thomas Publishing, Illinois. Zhang, L., Helander, M.G., Drury, C.G., 1996. Identifying factors of comfort and discomfort in sitting. Human Factors: Journal of the Human Factors and Ergonomics Society 38 (3), 377e389.