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The effects of latex gloves on the kinetics of grasping
International Journal of Industrial Ergonomics 28 (2001) 265–273
The effects of latex gloves on the kinetics of grasping R.H. Shih, E.M. Vasarhelyi, A. Dubrowski, H. Carnahan* Department of Kinesiology, University of Waterloo, Waterloo, Ont., Canada N2L 3G1 Received 20 July 2000; received in revised form 25 February 2001; accepted 9 March 2001
Abstract This study investigated the effect of the use of latex gloves on motor performance. In the first experiment ten participants performed sensory discrimination tests (a two-point discrimination and a Von Frey hair test) to assess the impact that varying layers of latex gloves (no glove, one, two or three layers of latex gloves) had on the tactile sensitivity of the index finger and thumb. Results showed that multiple layers of gloves impaired haptic sensitivity. To determine if impaired sensation affected motor control, in a second experiment participants picked up various masses (100, 150, 200 g) with their index finger and thumb in the same four glove conditions. Grip and load forces were recorded using a force transducer implanted in the target object. Results showed that more grip and load force was generated when participants were wearing multiple glove layers. However, it was also demonstrated that the gloves were more slippery than bare skin, suggesting that the increased grip forces observed when wearing gloves may have been related to lower friction between the object and glove surfaces. Relevance to industry The results of this study provide data on grip force production that can be used for designing tools and equipment and for potentially reducing the increased force production that is associated with repetitive strain injury. r 2001 Elsevier Science B.V. All rights reserved. Keywords: Grip force; Friction; Gloves
1. Introduction Latex gloves play an important role in the protection of workers, in health care settings, against contaminated body fluids. It is not an uncommon practice, in high risk situations, to wear multiple glove layers for extra protection as it has been shown that double gloving reduces the risk of exposure to contaminated body fluids (Chiu *Corresponding author. Fax: +1-519-885-0470. E-mail address: [email protected] (H. Carnahan).
et al., 1993; Endres et al., 1990; Sebold and Jordan, 1993). However, it has not been clearly established what effect multiple layers of gloves have on sensory and motor performance. In determining the ability to distinguish between different masses while wearing various types of gloves (surgical, Kevlar, rubber, nylon, cotton and leather), Shih and Wang (1996) had participants lift objects of two masses (ranging from 0.25 to 8.2 kg) simultaneously with the left and right hands. The participants fingers of each hand were in a power grip on a horizontal handle. Shih and Wang found no effect of glove use on the ability to
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distinguish between the masses. The authors proposed that for this type of task and the relatively large masses tested, heaviness may have been perceived through the hand and arm motor activity as opposed to just the fingers alone. In a similar earlier study using the same procedure, but testing only cotton and leather gloves, it was also found that glove type again had no effect on the ability to discriminate between various masses (Wang et al., 1991). Nelson and Mital (1995) compared the effect of varying glove thickness on tactile sensitivity and dexterity when picking up objects with different textures. They found that glove thickness had little effect on the ability of individuals to identify and pick up various grades of sandpaper, as well as with identifying the size of the objects they were touching. In addition, glove use did not affect the time required to use scissors to cut out various shapes. However, Muralidhar and Bishu (1994) examined how various types of gloves (latex, cotton, and leather) affected performance on a subset of Jebsen’s tests of hand performance (Jebsen et al., 1969) and did find some motor impairments related to glove use. They found that performance with the latex gloves on tasks such as flipping cards, stacking checkers, picking up small objects and moving objects, was quite similar to that of the bare hand, while the heavier gloves impaired motor performance. In a study conducted by Phillips et al. (1997), performance with either no glove, a single latex glove, or two latex glove layers was compared. It was found that multiple gloves degraded sensory performance (texture matching, point discrimination, stereognosis). Motor performance (time to pick up marbles, and the use of forceps to transfer objects) was also degraded with the multiple glove layers, but to a much lesser degree than the observed sensory impairment. In a more precise measure of motor performance, the amount of force generated on a handle when lifting various masses while wearing the protective gloves used by astronauts was examined (Bronkema et al., 1994). They found that the use of gloves had no influence on the amount of grip force produced. Instead, grip force was only
influenced by the size of the mass being lifted. The authors were surprised by the lack of a glove effect as they had expected that the heavy protective gloves tested would influence grip force control. However, they suggested that this lack of a glove effect may have been due to the increased coefficient of friction between the gloved hand and the handle relative to that of the bare hand and the handle (see Cadoret and Smith, 1996). That is, any expected increases in force production due to the glove were offset by the decreased need for force due to the higher coefficient of friction in the glove condition. While there is some consensus that dexterity and manipulation ability are decreased with glove use, force production appears to be unaffected. That is, while some studies have shown no motor impairments, other studies have shown decrements in performance related to glove use. One possible reason for this variation may be related to the role of sensory (haptic) input in motor performance. There appears to be some evidence of mild sensory deficit when gloves are worn (e.g., Nelson and Mital, 1995; Phillips et al., 1997). This could have implications for the control of movement since Johansson et al. (1992) have shown that force production could be impaired during complete anesthesia of the fingers. However, while wearing gloves may impair sensory function, it did not eliminate it. Thus, it is not clear if partial sensory input will also lead to decreased motor function in a manner similar to complete sensory loss. Another reason for the variable results when the relationship between glove use and motor performance was examined may be related to how motor performance was evaluated. In most of the experiments reviewed, the end result of a task was evaluated. That is, the ability of the participant to cut with scissors, or flip cards was examined. Either they could or could not perform the task. Very little attention was paid to the process or how the movements were carried out. Only in the Bronkema et al. (1994) study was the actual force produced by the hand during the movement measured. While this particular study showed no effects of glove use on force production, this was probably related to the nature of the task performed. That is, participants lifted a
R.H. Shih et al. / International Journal of Industrial Ergonomics 28 (2001) 265–273
weighted bar across their fingers much like carrying a suitcase. The adoption of a precision grip that requires the use of the index finger and thumb only when lifting small masses, as opposed to the power grip used in the Bronkema et al. (1994) study, may reveal more subtle adaptations in motor control strategies that are not seen when lifting heavy masses because the larger arm and back muscles and their associated proprioceptive receptors are not as active in this situation. This would allow for the examination of tasks that require more fine manipulation like those tasks that are typically performed by health care workers wearing latex gloves. Adaptations in force production may become apparent in tasks requiring the fine manipulation of small objects by the fingers because the delicate control required to avoid dropping this object can be quantified with force transducers. Thus, the purpose of the present study was to first examine if there is any evidence of reduced sensory abilities from latex glove use and second, to examine if motor abilities (quantified as force production by the index finger and thumb when lifting small objects) are influenced by the use of one, two or three layers of latex gloves.
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the Von Frey hair test were administered using standardized procedures on both the thumb and the index finger pads (Varney, 1986). Refer to Figs. 1 and 2 for a schematic showing the administration of these two tests. For the twopoint discrimination test, participants indicated whether they felt one or two points on their fingertips and thumbs (Varney, 1986). The experimenter held the apparatus from the end and its weight rested on the participants’ fingers. This procedure ensured that a constant force was applied to the fingers in all conditions. The minimum distance at which two points could be discriminated was analyzed in a repeated measures 4 condition (no glove, 1 glove, 2 gloves, 3 gloves) 2 digit (index finger, thumb) analysis of variance (ANOVA). Effect significant at po0.05 were further analyzed using the Tukey HSD posthoc method for comparison of means. For the Von Frey hair test, participants indicated if they felt the application of hairs of various diameters to the skin (Semmes et al., 1960). The hairs were pressed into the skin until they started to bend. Larger hairs (that were labeled with larger numbers) required more force to bend than smaller
2. Experiment 1 2.1. Methods 2.1.1. Participants A group of 10 right-handed students from the University of Waterloo (mean age=21.9 yr; range=19–26 yr) participated in this study. All participants gave informed consent and the project was given ethics approval by the University of Waterloo Office of Research. 2.1.2. Apparatus and procedures There were four conditions in this study. Participants wore either no glove (bare hand), one latex glove (President’s Choice, premiere quality), a double layer consisting of two latex gloves, or a triple layer consisting of three gloves, on their right hands. For each of the four conditions, the two-point discrimination test and
Fig. 1. The administration of the two-point discrimination test. The examiner held the apparatus at the end while it rested on the participant’s finger. The distance between the two points resting on the finger was progressively reduced until the participant could no longer discriminate the two points (depicted from panel A to B).
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Fig. 3. The minimum distance detected on the thumb and index finger as a function of the number of gloves worn.
Fig. 2. This figure shows the administration of the monofilament test. Force was applied by the experiment to hairs of various diameters until the hair started to bend (depicted from panel A to B). The participant was required to report whether or not felt the application on the hair was felt.
hairs (with smaller hair number labels), and thus this test was a measure of force sensitivity. Thus, the force of application across conditions was consistent because a constant amount of force was required to bend a particular hair in all experimental conditions. The hair number indicating the smallest diameter that could be detected was then analyzed in a repeated measures 4 condition (no glove, 1 glove, 2 gloves, 3 gloves) 2 digit (index finger, thumb) (ANOVA). 2.2. Results and discussion The two-point discrimination analysis showed a significant main effect for condition, F(3,27)=15.88, po0:01, and an interaction of
condition and digit, F(3,27)=3.1, po0:05. While the main effect showed that the sensitivity of the digits decreased as the number of gloves worn increased, when the fingers were examined separately, it was observed that there were no statistically significant differences across the glove conditions for the index finger. For the thumb, however, there was less sensitivity for the two and three gloved conditions in comparison to the no glove conditions. Refer to Fig. 3. The analysis of the data for the Von Frey hair test showed a main effect for condition, F(3,27) =20.21, po0:01. Similar to the results of the twopoint discrimination analysis, the no glove condition showed more sensitivity in the Von Frey hair test in comparison to the two and three glove conditions. The one glove condition differed only from the three glove condition and did not differ from the others (Fig. 4). No interaction of condition and digit was found. The findings from both perceptual tests suggest that the use of multiple layers of gloves (or in turn thicker gloves) does impair haptic sensitivity. It is not clear however, whether this degradation in haptic sensitivity influences motor output. Johansson et al. (1992) have suggested that after anesthesia of the digits, there are impairments in the tactile receptors. However, it has been suggested that a complete sensory block is needed to
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Fig. 5. A schematic of the grip used and the orientation of the force axes. The grip or normal force was defined by the z-axis, and forces in the x- and y-axis were perpendicular to the grip force and were combined to define the load force.
Fig. 4. The average minimum hair number that could be detected as a function of glove condition.
see these impairments. Does the relatively minor sensory impairment caused by glove influence our ability to manipulate objects? The second study was intended to address this question.
3. Experiment 2 3.1. Methods 3.1.1. Participants A group of 10 undergraduates of the University of Waterloo who did not participate in the first study (six males, four females with an age range of 20–23 yr), participated in the second experiment. All participants provided informed consent and this second project was also given ethics approval by the University of Waterloo Office of Research. 3.1.2. Apparatus and procedures All participants were seated in front of a table with their index fingers and thumbs resting in a relaxed pinch grip directly in front of the midline. They were instructed to reach toward and grasp a target object that was located 11 cm from the hand start position, and to lift it approximately 5 cm above the tabletop. A schematic of the grip used is shown in Fig. 5. The object to be grasped was a six-axis force-torque sensor (Nano F/T transducer; ATI Industrial Automation, Garner, NC) with two exchangeable polyethylene plastic cylindrical
mass containers with flat grasping surfaces, mounted on each side of the sensor. The resulting cylinder was 5.5 cm wide and 3 cm in diameter. Changing the mass containers on each side of the sensor varied the total mass of the unit. The unit’s total mass was either 100, 150 or 200 g. Thus, since the objects appeared visually identical, the only way participants could determine the mass of the objects was through haptics. When the target was lifted, the grip force was measured along the grip axis defined by the line joining the centers of the two grasping surfaces of the object. The forces were collected at 200 Hz with a resolution of 0.025 N. The load force was defined as the vector sum of the two perpendicular forces acting in the orthogonal plane to the grip force axis. The object was grasped while wearing either no glove, one glove, two gloves or three gloves. Ten trials of each condition were performed for each of the masses and for each glove condition resulting in a total of 120 total experimental trials. The trials were performed in a blocked fashion with the order of the presentation of the masses being randomized across participants for each glove condition. The order of the presentation of the glove conditions was also randomized across participants. After the completion of the experimental trials for each glove condition, two slip trials were performed in which the masses were held between the finger and thumb and slowly released until they dropped. The grip force at the moment the object began to slip between the fingers represented the minimum amount of force
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required to hold the object. The coefficient of friction was estimated by dividing the load force by the grip force at the moment of object slip (Cadoret and Smith, 1996). This method for estimating the coefficient of friction is similar to the procedures used by Armstrong (1985) and Westling and Johansson (1984) with the modification that in these previous studies, the participants had an external force pull the object from the participant’s hand rather than letting it drop voluntarily as in the present study. Westling and Johansson (1984) calculated the force at which the object in the hand began to slip and divided by the grip force to obtain an estimate of the coefficient of friction. This was similar to the calculations used in the present study. The ten trials for each condition were averaged for subsequent analyses. The magnitudes of peak grip and load force, and the estimated coefficients of friction, were analyzed in separate 3 target mass (100, 150, 200 g) 4 glove (no glove, 1 glove, 2 gloves, 3 gloves) repeated measures ANOVAs. ANOVA differences significant at po0:05 were further analyzed using the Tukey HSD method for posthoc comparison of means.
Fig. 6. Typical grip force curves for a single participant for each of the glove conditions.
3.2. Results and discussion 3.2.1. Grip force It should be noted that not one participant dropped the object in any of the experimental conditions. Thus, for the range of small masses tested in the present study, glove use did not influence grasping and lifting success. However, as seen in the grip force curves represented in Fig. 6, while the outcome (successful object lifting) is not affected by the gloves, the process that takes place to accomplish this is affected such that there was greater peak grip force when gloves were worn. The analysis of average peak grip force showed main effects for both object mass, F(2,18)=15.28, po0:01, and glove condition, F(3,27)=4.73, po0:01. As expected, grip force increased as object mass increased. Specifically, as seen in Fig. 7, less grip force was generated when grasping the 100 g mass in comparison to the 200 g mass. The grip force associated with the 150 g mass did not differ statistically from the other masses.
Fig. 7. Panel A shows the peak grip force as a function of glove condition. Panel B shows peak grip force as a function of object mass.
Furthermore, Fig. 7 shows that there was a trend that participants generated more force when they were wearing gloves in comparison to the no glove condition. That is, less force was generated in the
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Fig. 9. Coefficient of friction for each of the glove conditions. These values were obtained by dividing the load force by the grip force at the moment of object slip, during the slip trials, where participants held the object between the index finger and thumb and released force until the object dropped.
Fig. 8. Panel A shows the peak load force as a function of glove condition. Panel B shows peak load force as a function of object mass.
no glove condition in comparison to the one and three glove conditions. However, the amount of force generated in the two glove condition did not differ statistically from the no glove condition. There were no differences between the one, two and three glove conditions for the range of masses tested. 3.2.2. Load force Similar to grip force, the analysis of peak load force showed main effects for both target mass, F(2,18)=17.9, po0:01, and glove condition, F(3,27)=4.7, po0:01. Load force increased as target mass increased such that more load force was generated for each increasing target mass. Further, there was a trend for greater load force in the gloved conditions compared to the no glove conditions. However, only the three glove condition differed statistically from the no glove condition. Means are presented in Fig. 8. As expected, the pattern for load force is similar to
that of the grip force data since it has been shown that grip and load forces are correlated and vary together (Flanagan and Tresilian, 1994). 3.2.3. Coefficient of friction Analysis of the slip trials revealed that when holding the masses with the bare hand, the coefficient of friction was higher in comparison to either the one, two, or three glove conditions, which did not differ statistically from each other, F(3,27)=7.2, po0:01 (see Fig. 9). This findings indicates that there was less friction between the gloved gripping surface and the object, than the bare hand and object surface.
4. Conclusions The purpose of these studies was to examine whether there are sensory and motor deficits when wearing latex gloves. It was found that there was a sensory deficit associated with the use of multiple layers of latex gloves. This sensory deficit was reflected by an increase in force production during grasping and lifting objects. While functionally
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there was no impairment (no participant dropped the objects in the course of the study), the increased force production observed may create long term problems of fatigue and potential repetitive strain injury. Studies of ergonomic factors in the workplace (such as repetition, force, static muscle loading and extreme joint position) have found a strong causal relationship between jobs involving highly repetitive, forceful work and disorders of the neck and upper limbs (Stock, 1991; Viikari-Juntura et al., 1991). However, researchers have begun to recognize that even non-forceful, but highly repetitive tasks requiring people to use fewer and smaller muscles have greatly contributed to the surge in reported muscle, tendon or nerve entrapment disorders in the neck and upper limbs (Stock, 1991). Thus, for even highly repetitive, nonforceful tasks, a reduction of any unnecessary force production could directly reduce the incidence of repetitive strain injuries. However, it cannot be assumed that the decrease in haptic sensation was solely responsible for the increase in grip force. It was also found that glove use resulted in a lower estimated coefficient of friction between the object and the grasping surface (glove) which means that the gloves were more slippery than the bare fingers. This most likely contributed in part to the increased forces observed in the glove conditions but was probably not solely responsible because grip force was not stable across all gloved conditions, but increased as the number of gloves increased (and sensory impairment increased). It should be noted that it has previously been shown that load force typically does not increased as a function of friction in the same way as grip force (Cadoret and Smith, 1996). However, in the present study, both grip and load force increase as a function of the multiple glove layers. This suggests that the increased forces observed in the present study are probably related to sensory deprivation, and not just to a decreased coefficient of friction with the gloves. However, regardless of the mechanism, the practical problem of potential risk of repetitive strain injury due to increases in grip forces related to multiple latex glove usage still exists.
Acknowledgements This research was supported by a Natural Science and Engineering Research Council of Canada research grant awarded to H. Carnahan.
References Armstrong, T.J., 1985. Mechanical considerations of skin in work. American Journal of Industrial Medicine 8, 463–472. Bronkema, L.A., Garcia, D., Bishu, R.R., Klute, G., Rajulu, S., 1994. Tactility as a function of grasp force: the effects of gloves, pressure and load. In: Aghazedeh, F. (Ed.), Advances in Industrial Ergonomics and Safety VI. Taylor a Francis, London, pp. 627–632. Cadoret, G., Smith, A.M., 1996. Friction, not texture, dictates grip forces used during object manipulation. Journal of Neurophysiology 75, 1963–1969. Chiu, K.Y., Fung, B., Lau, S.K., Ng, K.H., Chow, S.P., 1993. The use of double latex gloves during hip fracture operations. Journal of Orthopaedic Trauma 7, 354–356. Endres, D., Alun-Jones, T., Morrissey, M.S., 1990. The effectiveness of double-gloving in otolaryngology. Clinical Orolarngology 15, 535–536. Flanagan, J.R., Tresilian, J.R., 1994. Grip-load force coupling: a general control strategy for transporting objects. Journal of Experimental Psychology: Human Perception and Performance 20, 944–957. Jebsen, R.H., Taylor, N., Triegehmann, R.B., Trotter, M.J., Howard, L.A., 1969. An objective and standardized test of hand function. Archives of Physical Medicine and Rehabilitation 50, 311. Johansson, R.S., Hager, C., Backstrom, L., 1992. Somatosensory control of precision grip during unpredictable pulling loads. III. Impairments during digital anesthesia. Experimental Brain Research 89, 204–213. Muralidhar, A., Bishu, R.R., 1994. Glove evaluation: a lesson from impaired hand testing. In: Aghezadeh, F. (Ed.), Advances in Industrial Ergonomics and Safety VI. Taylor a Francis, London, pp. 619–625. Nelson, J.B., Mital, A., 1995. An ergonomic evaluation of dexterity and tactility with increase in examination/surgical glove thickness. Egonomics 38, 723–733. Phillips, A.M., Birch, N.C., Ribbans, W.J., 1997. Protective gloves for use in high-risk patients: how much do they affect the dexterity of the surgeon? Annals of the Royal College of Surgeons England 79, 124–127. Sebold, E.J., Jordan, L.R., 1993. Intraoperative glove perforation. A comparative analysis. Clinical Orthopaedics and Related Research 7, 354–356. Semmes, J., Weinstein, S., Ghert, L., 1960. Somatosensory changes after penetrating brain wounds in man. Harvard University Press, Cambridge.
R.H. Shih et al. / International Journal of Industrial Ergonomics 28 (2001) 265–273 Shih, Y., Wang, M.J., 1996. The effects of weight levels and gloves on the ability to discriminate weight difference. Ergonomics 5, 729–739. Stock, S.R., 1991. Workplace ergonomic factors and the development of musculoskeletal disorders of the neck and upper limbs: a meta analysis. American Journal of Industrial Medicine 19, 87–107. Varney, N.R., 1986. Somethesis. In: H.J. Hanney (Ed.), Experimental Techniques in Human Neuropsychology. Oxford University Press, New York. Viikari-Juntura, E., Kurppa, K., Kuosma, E., Huuskonen, M., Kuorina, I., Ketola, R., Konni, U., 1991. Prevalence of
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epicondylitis and elbow pain in the meat-processing industry. Scandinavian Journal of Work, Environment and Health 17, 38–45. Wang, M.-J., Liu, C.-M., Shih, Y.-C., 1991. A method for determining the difference threshold of judging weight difference in material handling. International Journal of Industrial Ergonomics 8, 335–343. Westling, G., Johansson, R.S., 1984. Factors influencing the force control during precision grip. Experimental Brain Research 53, 277–284.
The effects of latex gloves on the kinetics of grasping R.H. Shih, E.M. Vasarhelyi, A. Dubrowski, H. Carnahan* Department of Kinesiology, University of Waterloo, Waterloo, Ont., Canada N2L 3G1 Received 20 July 2000; received in revised form 25 February 2001; accepted 9 March 2001
Abstract This study investigated the effect of the use of latex gloves on motor performance. In the first experiment ten participants performed sensory discrimination tests (a two-point discrimination and a Von Frey hair test) to assess the impact that varying layers of latex gloves (no glove, one, two or three layers of latex gloves) had on the tactile sensitivity of the index finger and thumb. Results showed that multiple layers of gloves impaired haptic sensitivity. To determine if impaired sensation affected motor control, in a second experiment participants picked up various masses (100, 150, 200 g) with their index finger and thumb in the same four glove conditions. Grip and load forces were recorded using a force transducer implanted in the target object. Results showed that more grip and load force was generated when participants were wearing multiple glove layers. However, it was also demonstrated that the gloves were more slippery than bare skin, suggesting that the increased grip forces observed when wearing gloves may have been related to lower friction between the object and glove surfaces. Relevance to industry The results of this study provide data on grip force production that can be used for designing tools and equipment and for potentially reducing the increased force production that is associated with repetitive strain injury. r 2001 Elsevier Science B.V. All rights reserved. Keywords: Grip force; Friction; Gloves
1. Introduction Latex gloves play an important role in the protection of workers, in health care settings, against contaminated body fluids. It is not an uncommon practice, in high risk situations, to wear multiple glove layers for extra protection as it has been shown that double gloving reduces the risk of exposure to contaminated body fluids (Chiu *Corresponding author. Fax: +1-519-885-0470. E-mail address: [email protected] (H. Carnahan).
et al., 1993; Endres et al., 1990; Sebold and Jordan, 1993). However, it has not been clearly established what effect multiple layers of gloves have on sensory and motor performance. In determining the ability to distinguish between different masses while wearing various types of gloves (surgical, Kevlar, rubber, nylon, cotton and leather), Shih and Wang (1996) had participants lift objects of two masses (ranging from 0.25 to 8.2 kg) simultaneously with the left and right hands. The participants fingers of each hand were in a power grip on a horizontal handle. Shih and Wang found no effect of glove use on the ability to
0169-8141/01/$ - see front matter r 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 8 1 4 1 ( 0 1 ) 0 0 0 2 1 - X
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distinguish between the masses. The authors proposed that for this type of task and the relatively large masses tested, heaviness may have been perceived through the hand and arm motor activity as opposed to just the fingers alone. In a similar earlier study using the same procedure, but testing only cotton and leather gloves, it was also found that glove type again had no effect on the ability to discriminate between various masses (Wang et al., 1991). Nelson and Mital (1995) compared the effect of varying glove thickness on tactile sensitivity and dexterity when picking up objects with different textures. They found that glove thickness had little effect on the ability of individuals to identify and pick up various grades of sandpaper, as well as with identifying the size of the objects they were touching. In addition, glove use did not affect the time required to use scissors to cut out various shapes. However, Muralidhar and Bishu (1994) examined how various types of gloves (latex, cotton, and leather) affected performance on a subset of Jebsen’s tests of hand performance (Jebsen et al., 1969) and did find some motor impairments related to glove use. They found that performance with the latex gloves on tasks such as flipping cards, stacking checkers, picking up small objects and moving objects, was quite similar to that of the bare hand, while the heavier gloves impaired motor performance. In a study conducted by Phillips et al. (1997), performance with either no glove, a single latex glove, or two latex glove layers was compared. It was found that multiple gloves degraded sensory performance (texture matching, point discrimination, stereognosis). Motor performance (time to pick up marbles, and the use of forceps to transfer objects) was also degraded with the multiple glove layers, but to a much lesser degree than the observed sensory impairment. In a more precise measure of motor performance, the amount of force generated on a handle when lifting various masses while wearing the protective gloves used by astronauts was examined (Bronkema et al., 1994). They found that the use of gloves had no influence on the amount of grip force produced. Instead, grip force was only
influenced by the size of the mass being lifted. The authors were surprised by the lack of a glove effect as they had expected that the heavy protective gloves tested would influence grip force control. However, they suggested that this lack of a glove effect may have been due to the increased coefficient of friction between the gloved hand and the handle relative to that of the bare hand and the handle (see Cadoret and Smith, 1996). That is, any expected increases in force production due to the glove were offset by the decreased need for force due to the higher coefficient of friction in the glove condition. While there is some consensus that dexterity and manipulation ability are decreased with glove use, force production appears to be unaffected. That is, while some studies have shown no motor impairments, other studies have shown decrements in performance related to glove use. One possible reason for this variation may be related to the role of sensory (haptic) input in motor performance. There appears to be some evidence of mild sensory deficit when gloves are worn (e.g., Nelson and Mital, 1995; Phillips et al., 1997). This could have implications for the control of movement since Johansson et al. (1992) have shown that force production could be impaired during complete anesthesia of the fingers. However, while wearing gloves may impair sensory function, it did not eliminate it. Thus, it is not clear if partial sensory input will also lead to decreased motor function in a manner similar to complete sensory loss. Another reason for the variable results when the relationship between glove use and motor performance was examined may be related to how motor performance was evaluated. In most of the experiments reviewed, the end result of a task was evaluated. That is, the ability of the participant to cut with scissors, or flip cards was examined. Either they could or could not perform the task. Very little attention was paid to the process or how the movements were carried out. Only in the Bronkema et al. (1994) study was the actual force produced by the hand during the movement measured. While this particular study showed no effects of glove use on force production, this was probably related to the nature of the task performed. That is, participants lifted a
R.H. Shih et al. / International Journal of Industrial Ergonomics 28 (2001) 265–273
weighted bar across their fingers much like carrying a suitcase. The adoption of a precision grip that requires the use of the index finger and thumb only when lifting small masses, as opposed to the power grip used in the Bronkema et al. (1994) study, may reveal more subtle adaptations in motor control strategies that are not seen when lifting heavy masses because the larger arm and back muscles and their associated proprioceptive receptors are not as active in this situation. This would allow for the examination of tasks that require more fine manipulation like those tasks that are typically performed by health care workers wearing latex gloves. Adaptations in force production may become apparent in tasks requiring the fine manipulation of small objects by the fingers because the delicate control required to avoid dropping this object can be quantified with force transducers. Thus, the purpose of the present study was to first examine if there is any evidence of reduced sensory abilities from latex glove use and second, to examine if motor abilities (quantified as force production by the index finger and thumb when lifting small objects) are influenced by the use of one, two or three layers of latex gloves.
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the Von Frey hair test were administered using standardized procedures on both the thumb and the index finger pads (Varney, 1986). Refer to Figs. 1 and 2 for a schematic showing the administration of these two tests. For the twopoint discrimination test, participants indicated whether they felt one or two points on their fingertips and thumbs (Varney, 1986). The experimenter held the apparatus from the end and its weight rested on the participants’ fingers. This procedure ensured that a constant force was applied to the fingers in all conditions. The minimum distance at which two points could be discriminated was analyzed in a repeated measures 4 condition (no glove, 1 glove, 2 gloves, 3 gloves) 2 digit (index finger, thumb) analysis of variance (ANOVA). Effect significant at po0.05 were further analyzed using the Tukey HSD posthoc method for comparison of means. For the Von Frey hair test, participants indicated if they felt the application of hairs of various diameters to the skin (Semmes et al., 1960). The hairs were pressed into the skin until they started to bend. Larger hairs (that were labeled with larger numbers) required more force to bend than smaller
2. Experiment 1 2.1. Methods 2.1.1. Participants A group of 10 right-handed students from the University of Waterloo (mean age=21.9 yr; range=19–26 yr) participated in this study. All participants gave informed consent and the project was given ethics approval by the University of Waterloo Office of Research. 2.1.2. Apparatus and procedures There were four conditions in this study. Participants wore either no glove (bare hand), one latex glove (President’s Choice, premiere quality), a double layer consisting of two latex gloves, or a triple layer consisting of three gloves, on their right hands. For each of the four conditions, the two-point discrimination test and
Fig. 1. The administration of the two-point discrimination test. The examiner held the apparatus at the end while it rested on the participant’s finger. The distance between the two points resting on the finger was progressively reduced until the participant could no longer discriminate the two points (depicted from panel A to B).
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Fig. 3. The minimum distance detected on the thumb and index finger as a function of the number of gloves worn.
Fig. 2. This figure shows the administration of the monofilament test. Force was applied by the experiment to hairs of various diameters until the hair started to bend (depicted from panel A to B). The participant was required to report whether or not felt the application on the hair was felt.
hairs (with smaller hair number labels), and thus this test was a measure of force sensitivity. Thus, the force of application across conditions was consistent because a constant amount of force was required to bend a particular hair in all experimental conditions. The hair number indicating the smallest diameter that could be detected was then analyzed in a repeated measures 4 condition (no glove, 1 glove, 2 gloves, 3 gloves) 2 digit (index finger, thumb) (ANOVA). 2.2. Results and discussion The two-point discrimination analysis showed a significant main effect for condition, F(3,27)=15.88, po0:01, and an interaction of
condition and digit, F(3,27)=3.1, po0:05. While the main effect showed that the sensitivity of the digits decreased as the number of gloves worn increased, when the fingers were examined separately, it was observed that there were no statistically significant differences across the glove conditions for the index finger. For the thumb, however, there was less sensitivity for the two and three gloved conditions in comparison to the no glove conditions. Refer to Fig. 3. The analysis of the data for the Von Frey hair test showed a main effect for condition, F(3,27) =20.21, po0:01. Similar to the results of the twopoint discrimination analysis, the no glove condition showed more sensitivity in the Von Frey hair test in comparison to the two and three glove conditions. The one glove condition differed only from the three glove condition and did not differ from the others (Fig. 4). No interaction of condition and digit was found. The findings from both perceptual tests suggest that the use of multiple layers of gloves (or in turn thicker gloves) does impair haptic sensitivity. It is not clear however, whether this degradation in haptic sensitivity influences motor output. Johansson et al. (1992) have suggested that after anesthesia of the digits, there are impairments in the tactile receptors. However, it has been suggested that a complete sensory block is needed to
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Fig. 5. A schematic of the grip used and the orientation of the force axes. The grip or normal force was defined by the z-axis, and forces in the x- and y-axis were perpendicular to the grip force and were combined to define the load force.
Fig. 4. The average minimum hair number that could be detected as a function of glove condition.
see these impairments. Does the relatively minor sensory impairment caused by glove influence our ability to manipulate objects? The second study was intended to address this question.
3. Experiment 2 3.1. Methods 3.1.1. Participants A group of 10 undergraduates of the University of Waterloo who did not participate in the first study (six males, four females with an age range of 20–23 yr), participated in the second experiment. All participants provided informed consent and this second project was also given ethics approval by the University of Waterloo Office of Research. 3.1.2. Apparatus and procedures All participants were seated in front of a table with their index fingers and thumbs resting in a relaxed pinch grip directly in front of the midline. They were instructed to reach toward and grasp a target object that was located 11 cm from the hand start position, and to lift it approximately 5 cm above the tabletop. A schematic of the grip used is shown in Fig. 5. The object to be grasped was a six-axis force-torque sensor (Nano F/T transducer; ATI Industrial Automation, Garner, NC) with two exchangeable polyethylene plastic cylindrical
mass containers with flat grasping surfaces, mounted on each side of the sensor. The resulting cylinder was 5.5 cm wide and 3 cm in diameter. Changing the mass containers on each side of the sensor varied the total mass of the unit. The unit’s total mass was either 100, 150 or 200 g. Thus, since the objects appeared visually identical, the only way participants could determine the mass of the objects was through haptics. When the target was lifted, the grip force was measured along the grip axis defined by the line joining the centers of the two grasping surfaces of the object. The forces were collected at 200 Hz with a resolution of 0.025 N. The load force was defined as the vector sum of the two perpendicular forces acting in the orthogonal plane to the grip force axis. The object was grasped while wearing either no glove, one glove, two gloves or three gloves. Ten trials of each condition were performed for each of the masses and for each glove condition resulting in a total of 120 total experimental trials. The trials were performed in a blocked fashion with the order of the presentation of the masses being randomized across participants for each glove condition. The order of the presentation of the glove conditions was also randomized across participants. After the completion of the experimental trials for each glove condition, two slip trials were performed in which the masses were held between the finger and thumb and slowly released until they dropped. The grip force at the moment the object began to slip between the fingers represented the minimum amount of force
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required to hold the object. The coefficient of friction was estimated by dividing the load force by the grip force at the moment of object slip (Cadoret and Smith, 1996). This method for estimating the coefficient of friction is similar to the procedures used by Armstrong (1985) and Westling and Johansson (1984) with the modification that in these previous studies, the participants had an external force pull the object from the participant’s hand rather than letting it drop voluntarily as in the present study. Westling and Johansson (1984) calculated the force at which the object in the hand began to slip and divided by the grip force to obtain an estimate of the coefficient of friction. This was similar to the calculations used in the present study. The ten trials for each condition were averaged for subsequent analyses. The magnitudes of peak grip and load force, and the estimated coefficients of friction, were analyzed in separate 3 target mass (100, 150, 200 g) 4 glove (no glove, 1 glove, 2 gloves, 3 gloves) repeated measures ANOVAs. ANOVA differences significant at po0:05 were further analyzed using the Tukey HSD method for posthoc comparison of means.
Fig. 6. Typical grip force curves for a single participant for each of the glove conditions.
3.2. Results and discussion 3.2.1. Grip force It should be noted that not one participant dropped the object in any of the experimental conditions. Thus, for the range of small masses tested in the present study, glove use did not influence grasping and lifting success. However, as seen in the grip force curves represented in Fig. 6, while the outcome (successful object lifting) is not affected by the gloves, the process that takes place to accomplish this is affected such that there was greater peak grip force when gloves were worn. The analysis of average peak grip force showed main effects for both object mass, F(2,18)=15.28, po0:01, and glove condition, F(3,27)=4.73, po0:01. As expected, grip force increased as object mass increased. Specifically, as seen in Fig. 7, less grip force was generated when grasping the 100 g mass in comparison to the 200 g mass. The grip force associated with the 150 g mass did not differ statistically from the other masses.
Fig. 7. Panel A shows the peak grip force as a function of glove condition. Panel B shows peak grip force as a function of object mass.
Furthermore, Fig. 7 shows that there was a trend that participants generated more force when they were wearing gloves in comparison to the no glove condition. That is, less force was generated in the
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Fig. 9. Coefficient of friction for each of the glove conditions. These values were obtained by dividing the load force by the grip force at the moment of object slip, during the slip trials, where participants held the object between the index finger and thumb and released force until the object dropped.
Fig. 8. Panel A shows the peak load force as a function of glove condition. Panel B shows peak load force as a function of object mass.
no glove condition in comparison to the one and three glove conditions. However, the amount of force generated in the two glove condition did not differ statistically from the no glove condition. There were no differences between the one, two and three glove conditions for the range of masses tested. 3.2.2. Load force Similar to grip force, the analysis of peak load force showed main effects for both target mass, F(2,18)=17.9, po0:01, and glove condition, F(3,27)=4.7, po0:01. Load force increased as target mass increased such that more load force was generated for each increasing target mass. Further, there was a trend for greater load force in the gloved conditions compared to the no glove conditions. However, only the three glove condition differed statistically from the no glove condition. Means are presented in Fig. 8. As expected, the pattern for load force is similar to
that of the grip force data since it has been shown that grip and load forces are correlated and vary together (Flanagan and Tresilian, 1994). 3.2.3. Coefficient of friction Analysis of the slip trials revealed that when holding the masses with the bare hand, the coefficient of friction was higher in comparison to either the one, two, or three glove conditions, which did not differ statistically from each other, F(3,27)=7.2, po0:01 (see Fig. 9). This findings indicates that there was less friction between the gloved gripping surface and the object, than the bare hand and object surface.
4. Conclusions The purpose of these studies was to examine whether there are sensory and motor deficits when wearing latex gloves. It was found that there was a sensory deficit associated with the use of multiple layers of latex gloves. This sensory deficit was reflected by an increase in force production during grasping and lifting objects. While functionally
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there was no impairment (no participant dropped the objects in the course of the study), the increased force production observed may create long term problems of fatigue and potential repetitive strain injury. Studies of ergonomic factors in the workplace (such as repetition, force, static muscle loading and extreme joint position) have found a strong causal relationship between jobs involving highly repetitive, forceful work and disorders of the neck and upper limbs (Stock, 1991; Viikari-Juntura et al., 1991). However, researchers have begun to recognize that even non-forceful, but highly repetitive tasks requiring people to use fewer and smaller muscles have greatly contributed to the surge in reported muscle, tendon or nerve entrapment disorders in the neck and upper limbs (Stock, 1991). Thus, for even highly repetitive, nonforceful tasks, a reduction of any unnecessary force production could directly reduce the incidence of repetitive strain injuries. However, it cannot be assumed that the decrease in haptic sensation was solely responsible for the increase in grip force. It was also found that glove use resulted in a lower estimated coefficient of friction between the object and the grasping surface (glove) which means that the gloves were more slippery than the bare fingers. This most likely contributed in part to the increased forces observed in the glove conditions but was probably not solely responsible because grip force was not stable across all gloved conditions, but increased as the number of gloves increased (and sensory impairment increased). It should be noted that it has previously been shown that load force typically does not increased as a function of friction in the same way as grip force (Cadoret and Smith, 1996). However, in the present study, both grip and load force increase as a function of the multiple glove layers. This suggests that the increased forces observed in the present study are probably related to sensory deprivation, and not just to a decreased coefficient of friction with the gloves. However, regardless of the mechanism, the practical problem of potential risk of repetitive strain injury due to increases in grip forces related to multiple latex glove usage still exists.
Acknowledgements This research was supported by a Natural Science and Engineering Research Council of Canada research grant awarded to H. Carnahan.
References Armstrong, T.J., 1985. Mechanical considerations of skin in work. American Journal of Industrial Medicine 8, 463–472. Bronkema, L.A., Garcia, D., Bishu, R.R., Klute, G., Rajulu, S., 1994. Tactility as a function of grasp force: the effects of gloves, pressure and load. In: Aghazedeh, F. (Ed.), Advances in Industrial Ergonomics and Safety VI. Taylor a Francis, London, pp. 627–632. Cadoret, G., Smith, A.M., 1996. Friction, not texture, dictates grip forces used during object manipulation. Journal of Neurophysiology 75, 1963–1969. Chiu, K.Y., Fung, B., Lau, S.K., Ng, K.H., Chow, S.P., 1993. The use of double latex gloves during hip fracture operations. Journal of Orthopaedic Trauma 7, 354–356. Endres, D., Alun-Jones, T., Morrissey, M.S., 1990. The effectiveness of double-gloving in otolaryngology. Clinical Orolarngology 15, 535–536. Flanagan, J.R., Tresilian, J.R., 1994. Grip-load force coupling: a general control strategy for transporting objects. Journal of Experimental Psychology: Human Perception and Performance 20, 944–957. Jebsen, R.H., Taylor, N., Triegehmann, R.B., Trotter, M.J., Howard, L.A., 1969. An objective and standardized test of hand function. Archives of Physical Medicine and Rehabilitation 50, 311. Johansson, R.S., Hager, C., Backstrom, L., 1992. Somatosensory control of precision grip during unpredictable pulling loads. III. Impairments during digital anesthesia. Experimental Brain Research 89, 204–213. Muralidhar, A., Bishu, R.R., 1994. Glove evaluation: a lesson from impaired hand testing. In: Aghezadeh, F. (Ed.), Advances in Industrial Ergonomics and Safety VI. Taylor a Francis, London, pp. 619–625. Nelson, J.B., Mital, A., 1995. An ergonomic evaluation of dexterity and tactility with increase in examination/surgical glove thickness. Egonomics 38, 723–733. Phillips, A.M., Birch, N.C., Ribbans, W.J., 1997. Protective gloves for use in high-risk patients: how much do they affect the dexterity of the surgeon? Annals of the Royal College of Surgeons England 79, 124–127. Sebold, E.J., Jordan, L.R., 1993. Intraoperative glove perforation. A comparative analysis. Clinical Orthopaedics and Related Research 7, 354–356. Semmes, J., Weinstein, S., Ghert, L., 1960. Somatosensory changes after penetrating brain wounds in man. Harvard University Press, Cambridge.
R.H. Shih et al. / International Journal of Industrial Ergonomics 28 (2001) 265–273 Shih, Y., Wang, M.J., 1996. The effects of weight levels and gloves on the ability to discriminate weight difference. Ergonomics 5, 729–739. Stock, S.R., 1991. Workplace ergonomic factors and the development of musculoskeletal disorders of the neck and upper limbs: a meta analysis. American Journal of Industrial Medicine 19, 87–107. Varney, N.R., 1986. Somethesis. In: H.J. Hanney (Ed.), Experimental Techniques in Human Neuropsychology. Oxford University Press, New York. Viikari-Juntura, E., Kurppa, K., Kuosma, E., Huuskonen, M., Kuorina, I., Ketola, R., Konni, U., 1991. Prevalence of
273
epicondylitis and elbow pain in the meat-processing industry. Scandinavian Journal of Work, Environment and Health 17, 38–45. Wang, M.-J., Liu, C.-M., Shih, Y.-C., 1991. A method for determining the difference threshold of judging weight difference in material handling. International Journal of Industrial Ergonomics 8, 335–343. Westling, G., Johansson, R.S., 1984. Factors influencing the force control during precision grip. Experimental Brain Research 53, 277–284.