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Ergonomic comparison between a ‘right angle’ handle style and standard style paint brush: An electromyographic analysis
International Journal of Industrial Ergonomics 56 (2016) 130e137
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International Journal of Industrial Ergonomics journal homepage: www.elsevier.com/locate/ergon
Ergonomic comparison between a ‘right angle’ handle style and standard style paint brush: An electromyographic analysis James Agostinucci*, John McLinden Physical Therapy Department, University of Rhode Island, 25 West Independence Way, Kingston, RI, USA
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 March 2015 Received in revised form 24 May 2016 Accepted 24 September 2016
Background: Epidemiologic studies have consistently demonstrated a strong positive association between repetition and “occupational overuse syndromes” (OOS). The repetitive nature of painting then can predispose many people to these disorders. Objective: The purpose of this study was to conduct an electromyographic analysis (EMG) comparing a right angle handle paint applicator with a commonly used, equal quality standard handle paint brush. Method: A randomized cross over repeated measures design was implemented where 30 volunteers were randomly given a paint brush handle type while muscle activity (EMG) was recorded from eight upper limb muscles groups. Subjects were their own controls returning within one week to perform the same painting activity with the other paint brush handle type. ANOVA with repeated measures was used to analyze the EMG data among muscles between the two painting trials. Results: EMG analysis revealed that there was no difference in EMG activity or median frequency between the two types of paint brush handles in the eight muscles studied (p > 0.05). Conclusion: A right angle handle has no added ergonomic advantage in modifying muscle activity or decreasing muscle fatigue over a commonly used standard handle paint brush in people without injury. It was suggested that the right angle style brush may not prevent OOSs from occurring, although there still could be a decrease risk of injury based on the posture used when gripping the brush handle. It must be emphasized, however, that this study's results cannot be extrapolated to people who already have an OOS and need a device to prevent further injury and pain. Further study is needed. © 2016 Elsevier B.V. All rights reserved.
Keywords: Occupational overuse syndromes Repetitive strain injury Work-related musculoskeletal disorders Carpal tunnel syndrome Trigger finger De Quervain's disease
1. Introduction The principle behind ergonomic tools is to increase productivity by reducing fatigue, increasing comfort and lowering the risk of injury. Ergonomically designed hand-held tools attempt to increase biomechanical efficiency by manipulating hand and wrist position (Koningsveld et al., 2005; Dale et al., 2013). Wrist and hand positions have a significant impact on muscle groups recruited (Carey and Gallwey, 2005; Mell et al., 2006), discomfort, and on the possibility of causing trauma (Feuerstein et al., 1998; Barr et al., 2004; Bureau of Labor and Statistics, 2004; Duke et al., 2004; Fung et al., 2007; Fischer et al., 2009) therefore ergonomic designs have a significant degree of necessity. Epidemiologic studies have shown a significant positive correlation between Carpal Tunnel Syndrome (CTS) and certain risk factors such as repetition, force, wrist
* Corresponding author. E-mail address: [email protected] (J. Agostinucci). http://dx.doi.org/10.1016/j.ergon.2016.09.008 0169-8141/© 2016 Elsevier B.V. All rights reserved.
position (Barr et al., 2004; Bureau of Labor and Statistics, 2004) and increased muscle activity (Fagarasanu et al (2004; Finneran and O'Sullivan, 2013; Roman-Liu and Bartuzi, 2013)., especially when there is a combination of these risk factors. Repetitive motion musculoskeletal disorders (RMD's), such as CTS, Lateral Epicondylitis (LE) and other enthesopathies of the upper extremity associated with poor wrist position, have been shown to significantly increase the numbers of missed work days (Barr et al., 2004; Dale et al., 2013; Petit et al., 2015). According to the Bureau of Labor and Statistics (2004), an average of 20 work-days are missed each year per instance due to repetitive motion wrist injuries. Health care costs for federal workers over the course of a one year study for these types of claims were $12, 228, 755,228,755 with an average individual cost of $2849 and the average indemnity cost was approximately $4700 (Feuerstein et al., 1998). These findings indicate that while upper extremity disorders represent a relatively small percentage of all workers' compensation cases, the health care and indemnity costs are considerable (Feuerstein et al., 1998).
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Painting has an inherent risk for developing “occupational overuse syndromes” (OOS) due to the repetitive nature of the task, and epidemiologic studies have consistently demonstrated a strong positive association between repetition and RMD's (Thomsen et al., 2007; National Institute of Occupational Safety & Health, 2012). Decreasing the risks associated with painting has the potential to impact a significant portion of the population. The International Union of Painters and Allied Tradesmen (IUPAT) is comprised of 140,000 reported members within the United States and Canada, who are predominantly employed in the construction industry (Hamre et al., 2009). Painting is also a common do-it-yourself home improvement task. These factors increase the potential positive impact of an ergonomically designed painting tool. Standard paint brush handle types require a wrist position that have been shown to increase in the myoelectric activity of muscles linked to repetitive strain injury (Duke et al., 2004; Fagarasanu et al., 2004; Finneran and O'Sullivan, 2013; Roman-Liu and Bartuzi, 2013). The more glaring effect of handle type on wrist position was excessive ulnar deviation (Matern et al., 1999; Duke et al., 2004). Ulnar deviation was shown to produce a significantly greater amount of muscle activity compared to more neutral wrist positions (Fagarasanu et al., 2004; Roman-Liu and Bartuzi, 2013). In the case of an axial or “screwdriver” type handle, the handle is in line with the long axis of the forearm resulting in increased ulnar deviation, (Matern et al., 1999; Koningsveld et al., 2005; Mell et al., 2006; Fischer et al., 2009; Hamre et al., 2009). Therefore, any ergonomic device that promotes the wrist neutral position, theoretically, would be superior in preventing injuries. There are many ergonomically designed hand-held paintbrushes currently available commercially. One ergonomic design employs a right-angle handle position. A more neutral wrist position can be maintained with a bent handle tool, the axis of which is perpendicular to the long axis of the limb (Duke et al., 2004). Standard paint brushes are typically held in the same position as other screwdriver-type handles, while “right angle” paint brushes employ a bent handle, which encourages a neutral wrist position and can potentially recruit muscle groups less prone to fatigue. Since Finneran and O'Sullivan (2013) and others (Young et. al. 2013; Szeto and Ng, 2000) showed grip type had a highly significant effect on forearm muscle activity (EMG) of all the muscles they tested, assessing muscle activity through surface EMG may be an easy and effective way of evaluating the ergonomic value between the two brush types. Lastly, the use of axial type handles require a more precision grip that recruits the smaller more fatigable hand muscles. Higher precision requirements often slow tasks and reduces output. The additional time it takes to complete a task while in a stressed position further increases the probability of obtaining an OOS (Finneran and O'Sullivan, 2013). Comparing muscle activity from hand, forearm and other upper extremity muscles will provide important information to show which muscles are more actively involved between the two brush handle types. The purpose of this pilot study was to evaluate the muscle activity (EMG) of upper limb muscles associated with the standard hand-held paint brush and a commercially available “right angle” paint brush, called the ‘Right Brush®’, to make a comparison between the two. The ‘Right Brush®’ claims to decrease the probability of acquiring RMD's and other related disorders by promoting use of larger proximal muscles that are less prone to fatigue and prevent inappropriate hand/wrist positions (Wholey, The Right Brush®, 2013). While a particular handle type may appear more ergonomically correct, it still may result in similar musculoskeletal abnormalities (Duke et al., 2004). Results will evaluate whether the design of the ‘Right Brush®’ is a viable ergonomic alternative.
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2. Materials and methods 2.1. Subjects Thirty healthy volunteers were recruited using flyers placed in various stores that sell painting supplies, around the local community, and by word of mouth. Inclusion criteria for this study were participants were between the ages of 18e65, had some previous painting experience, and had no history of musculoskeletal or neuromuscular disorders of the dominant upper limb. All participants read and signed an informed consent form approved by the University of Rhode Island Institutional Review Board and completed a general health questionnaire. The study took place in a well ventilated room to ensure safety of the participants and researchers. 2.2. Materials A 40 70 wooden structure was constructed for subjects to paint (Figs. 1 and 2) This structure simulated commonly painted areas of a house including trim, a bookshelf and fixtures. The structure was used a total of 15 times, receiving 30 coats of paint on each side, after which it was replaced with an identical structure. Areas of the structure were labeled one through six, with areas one through four located on the front and areas five and six located on the back (Figs. 1 and 2). This was done to standardize location of painting during electromyographic recordings for statistical analysis. Acrylic based paints were used for safety purposes. Acrylic based paints give off less fumes and can be cleaned with regular soap and warm water. Two different neutral paint colors were used to differentiate between participant's trials. Paint brushes used included a standard paint brush (Fig. 3) with the traditional, screwdriver type handle and the newly designed ‘Right Brush®’ (Fig. 4) with a right-angled handle encouraging a right angle grip. Both brushes were of similar weights and 2 ½ inches wide with polyester-nylon bristles. Both paint brushes were made by ArrowWorthy®. EMG: An 8- channel wireless blue-tooth electromyograph (EMG) (PS 850 Data Log, Biometrics Ltd., UK) was used to record upper limb muscle activity. Bipolar AgeAgCl surface electrodes
Fig. 1. Structure front with numbers.
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Fig. 2. Structure back with numbers.
Fig. 3. Standard brush.
Fig. 5. EMG attachment on participant.
of 30 min (seven total recordings). Each recording lasted 10 s. The myoelectric signals were digitized at 1000 Hz at a bandwidth of 20e450 Hz and stored on a designated computer for future analysis. The EMG's amplifier had an input impedance of 1 MΏ (4730 pf), a common Mode Rejection ratio of 96 dB @ 50 Hz and a signal to noise ratio of <1 m V r.m.s. 2.3. Experimental procedure
Fig. 4. The right Brush®.
were placed on the skin over the abductor pollicus brevis (APB), flexor carpi radialis (FCR) and extensor digitorum (ED), biceps and triceps, anterior deltoid muscle, upper trapezius, and the clavicular portion of the pectoral major muscle of the dominant arm. It must be emphasized that surface EMG record myoelectric potentials from all the muscles within the territory of the surface electrode and the specific muscles were mentioned for only description purposes to identify the exact location that the EMG electrodes were placed. (Pullman et al., 2000). The muscle groups lying under the electrodes were chosen according to the muscle actions required of the upper extremity during painting activities, including, grip, wrist stability, activity at the elbow, and shoulder flexion. The ground electrode was placed on the lateral malleolus of the ankle contralateral to each participant's dominant hand. A belt was used to secure the DataLog base to the participant's waist and pre-wrap straps, to allow free movement of the upper extremity during painting (Fig. 5). EMG recordings were taken at initiation of painting (baseline) and at 5 min intervals for duration
The experiment began by randomly giving the participant the ‘Right Brush®’ or the standard paint brush with an open gallon of paint. Painters were allowed to hold the brush in any way they deemed comfortable throughout the trial. Once the EMG electrodes, wires and DataLog base were secured, participants were instructed to begin practice painting motions until they felt comfortable using the paintbrush. Participants were instructed to start painting anywhere on the structure and their goal was to paint both sides. Participants were allowed to paint freely for 5 min, at which time they were directed to the numbered areas on the structure (Figs. 1 and 2), where they were instructed to paint for a minimum of 10 s. EMG recordings were taken during this 10 s interval. After the 10 s participants were instructed to continue painting freely. This process continued until all 6 numbered areas were painted. The numbered areas were painted in the same order and at the same point in every trial to ensure consistency of EMG data for statistical analysis. The participants were also observed to ensure that EMG recording were taken only during painting and not when the subject was performing other painting-related activities (i.e. dipping the brush into the paint can). Upon completion of the task, participants were asked to rate their subjective fatigue level from the upper limb they used in painting with special attention to the areas where surface electrodes were placed for each of the brush handle types. Rating were conducted on a visual analog chart (VAS) (Fig. 6). Participants returned within one to seven days to complete the same experimental procedure using the alternate brush. Each participant therefore painted the wooden structure twice using a different brush each time.
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Table 1 Participant demographics. Number of Participants
Fig. 6. Fatigue visual analog scale.
2.4. EMG analysis EMG data was downloaded to the designated computer and was analyzed using the Biometrics DataLOG analysis software. To provide a way of reducing the amount of error arising from natural variance between individuals each participant severed as their own controls In addition, since EMG values depend closely on personal characteristics, measuring their values across individuals and comparing them between tests require normalization to some type of reference. Customarily the average of 1e4 maximum voluntary contractions is used as the reference value (Mathiassen et al., 1995; Gallagher et al., 2011). In this study, having subjects maximally contract 1e4 times for each of the eight muscle groups was fatiguing and not practical. Therefore we chose to normalize EMG data by having the subject paint for 10 s before the 1st trial EMG was recorded and use this initial EMG recording as the reference that all other EMG trials were compared to for that EMG session (Roman-Liu et al., 2013). Care was taken to assure that the reference EMGs were recorded during painting activities that were similar among painting sessions and subjects. Two EMG analyses were performed from the raw signals; area under the curve and Median frequency (MF). For the area under the curve analysis, the raw EMG signal was full wave rectified, filtered at 20 to 500 KHz and integrated (area under the curve) for each of the six 10 s recording, for each muscle, for each brush handle type.” Median frequency was calculated from the same raw EMG signals using the “Biometrics DataLOG analysis software” median frequency filter. A sliding window technique with a step size of 500 samples and a window size of 10,000 samples. Refer to www.biometricsltd.com/filters.htm for detailed information about this methodology. MF values were plotted for each muscle. 2.5. Statistical analysis Statistical analysis used the ratios of the EMGs (trial EMG/ reference EMG) and any change in these ratios determined its significance. Each 10 s recording interval was defined as one trial. There were 6 trials taken within a 30 min painting activity. OneWay ANOVA's with two repeated measures (brush type, trials) was used to compare each muscle's myoelectric activity between the two brush types. The subjective fatigue level that was gathered from the VAS was analyzed using the signed rank test to determine if there was a difference between the paint brushes. A non-parametric test were was used because the data were not normally distributed. 3. Results Five participants were omitted from data analysis due to premature terminating the experiment (2 participants) or had unstable EMG recordings (3 participants). Of the 25 subjects that completed the study, there were 10 males and 15 females, 23 righthand dominant and two left-hand dominant, 24 novice painters and one a professional painter. Refer to Table 1 one for participant demographics.
Age Range 18e30 30e45 45e65 Gender Male Female Dominant Hand Left Hand Right Hand
21 1 3 10 15 2 23
3.1. EMG and median frequency data Figs. 7 and 8 show a representation of the mean integrated EMG from the thenar and dorsal forearm muscle groups. As can be observed from the graph, there was not any difference in muscle activity between the two brush handle types. All other muscle groups showed similar non-significant results. Figs. 9 and 10 show the mean median frequency from the triceps and upper trapezius muscle groups in all 25 subjects. As in EMG integrated data, the differences between the median frequencies between the two handle types were also similar and insignificant for all seven muscle groups. The only exception in median frequency data was from the APB muscle (Fig. 11). Median frequencies from this muscle were very stable over time and. did not decline as it did for the other six muscle groups. Since the APB did not show the same fatigue characteristics as the other muscle groups it was concluded that the larger extrinsic hand muscles were more important in holding onto the paint brush handles. Differences between the two handle types for this muscle were again not significant. 3.2. Questionnaire data Participants rated the ‘Right Brush®’ generally less fatiguing (Figs. 12 and 13), (p < 0.05). In it noteworthy to mention, that the subjective fatigue ratings from many individuals did not correspond with their MF data. These responses may be related to the phenomenon known as the Hawthorne effect, where people perform or rate items as superior merely because they expect it to be better (Portney and Watkins, 2000). This interpretation, however, is purely speculative. It is quite possible participant's subjective fatigue level increase legitimately and our method of assessment (MF) was inadequate. Interestingly, the one subject who identified themselves as a professional painter (subject 19 in Fig. 13) rated the ‘Right Brush® substantially more fatiguing. 4. Discussion Work-related musculoskeletal disorders (WMSDs) have become one main focus in occupational disease prevention (Laoopugsin and Laoopugsin, 2012). In particular, upper limb WMSDs (WMSDs-UL) are today the commonest forms of occupational disease in many parts of the industrialized world (Aptel et al., 2002; Colombini and Occhipinti, 2006; Nicoletti et al., 2008). Numerous epidemiological studies conducted during the last 20 years have provided data supporting causal relationships between exposure to work-related risk factors and the development of WMSDs-UL. Barr et al. (2004), Bongers et al. (2006) and Laoopugsin and Laoopugsin (2012) showed that prolonged, highly repetitive and forceful hand-wrist tasks are the most common factors causing WMSDs such as carpal tunnel syndrome (CTS). From the conclusions of these studies it
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Fig. 7. Thenar Muscle Activity. Plots represent the amount of muscle activity for each time interval during the experiment for the two brushes. Each point represents the average ratios in millivolts (mV) from the integrated EMG (IEMG) of all subjects over a 10 s period. (p > 0.05). Standard deviations are also shown.
Fig. 8. Forearm Extensor Muscle Activity. Plots represent the amount of muscle activity for each time interval during the experiment for the two brushes. Each point represents the average ratios in millivolts (mV) from the integrated EMG (IEMG) of all subjects over a 10 s period. (p > 0.05). Standard deviations are also shown.
Fig. 9. Posterior arm muscle group median frequency (MF). Plots represent the MFs for each time interval during the experiment for the two brushes. Each point represents the average ratios in Hertz (HZ) from the EMG power spectral analysis (MF interval/MF baseline). (p > 0.05). Standard deviations are also shown.
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Fig. 10. Upper trapezius median frequency (MF). Plots represent the MFs for each time interval during the experiment for the two brushes. Each point represents the average ratios in Hertz (Hz) from the EMG power spectral analysis (MF interval/MF baseline).
MF interval/ MF baseline (Hz)
2.0
1.5 Right Brush Standard Brush 1.0
0.5
0.0 0.1
5
10
15
Time (minutes)
20
25
30
Fig. 11. Thenar muscle group median frequency (MF). Plots represent the MFs for each time interval during the experiment for the two brushes. Each point represents the average ratios in Hertz (Hz) from the EMG power spectral analysis (MF interval/MF baseline).
Fig. 12. Subjective mean fatigue level. Average visual analog scale determinations from 25 subjects. Standard deviations are also shown. Subjects rated the ‘Right Brush® slightly less fatiguing (p < 0.05).
was recommended more attention be brought to hand function of employees in the work place since today WMSDs-UL are the most common forms of occupational disease accountings for more than 45% of all occupational diseases (European Agency for Safety and Health at work, 2014). In this study we used ‘painting’ as the task to study upper extremity muscle activity and fatigue. Painting encompasses many risk factors that lead to WMSDs-UL including CTS (Palmer, 2011; Petit et al., 2015). It is a prolonged activity, is repetitive, requires isometric and isokinetic muscle contractions of all upper limb muscles including the hand, and may place the wrist in several distinct positions that have been shown to increase the probability of developing WMSDs-UL (Carey and Gallwey, 2005). The main findings of this study showed that the myoelectric activity required to hold and paint with the ‘Right Brush®’ was no different from that of a standard brush. This suggests that a “right angle handle” paint brush handle has no ergonomic benefit over a standard paint brush handle in lowering muscle activity or
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Fig. 13. Scatter plot of Individual fatigue ratings ratios. Participants gave their subjective fatigue levels by choosing a number from 1 to 10 on a visual analog scale where 1 was no fatigue and 10 was sever fatigue (exhausting). Y axis represents the ratio of the subject fatigue ratings from Right brush/standard brush. Response of 1 indicates no difference in fatigue levels between the brushes. Values under 1 represents less fatigue when using the ‘Right Brush® and levels over 1 indicate that the standard brush was less fatiguing. Subjects rated the ‘Right Brush® less fatiguing (p < 0.05).
decreasing fatigue. The muscle activity used to hold onto the paint brush handle as well as the painting strokes (movement) of the other upper extremity muscles are therefore not determined by the handle type but rather by other aspects specific to the individual painter. This was demonstrated during the experiment. As time progressed, participants were observed casually changing grips (Fig. 14aec) and altering their strokes probably adjusting to fatiguing muscles. These compensatory patterns are (likely) utilized to adjust to muscle fatigue while attempting to maintain appropriate forces required to continue painting effectively and comfortably. Figs. 10 and 11 demonstrate these phenomena in the triceps and upper trapezius muscles. As can be seen from the figures, the median frequency (MF) appears to decrease from the start of painting to approximately 20 min as painting progresses. This is a normal response to fatigue. However, around 20e25 min, a large increase in MF occurred. Coincidentally, it was noticed in many participants that at the time of the MF increase a grip/position change occurred at approximately the same time take place resulting in a change in their overall painting technique. This MF change was also seen in the other muscles recorded from except the abductor pollicis brevis, which showed a more stable fatigue level (Fig. 10.). This study's protocol had participants paint with one type of brush handle and then returning one to seven days later and painting again using the other brush (within participant design). The paint handle, therefore, was the only variable that changed. Participants were carefully
guided through the painting process so that each muscle was recorded while the subject painted the same part of the jig. This insured a consistent EMG comparison between trials. Referring to all the EMG Figs. 7e11 it can be seen that the traces between each muscle are almost identical even though the second day of painting was three to seven days later. These results strongly suggest that participants use the same painting technique whether they used a right angle handle or a standard handle paint handle. The results of this study suggest that if the goal is to prevent injury, the postures used during the task may have more impact than the tool used, regardless of the tool's face validity. When considering strategies to decrease injury, emphasis should be placed on correct body mechanics principles so that the physical activity is performed properly in addition to tool design considerations. This proposition is in accordance with the findings of Fagarasanu et al. (2004) and Finneran and O'Sullivan (2013) who showed that the neutral wrist position significantly decreases muscle activity. These results suggest the neutral wrist posture will reduce the risk of injuries. Therefore, based on our finding, prescribing only an ergonomically designed tool without proper instruction may have no beneficial effect. It should be emphasized that we did not directly measure the effect that hand/wrist posture had on inducing or preventing injury. Studies have shown that certain grip/wrist positions are directly related to the increased prevalence of CTS (Laoopugsin and Laoopugsin (2012), de Quervain's disease and trigger finger (Ryzewicz and Wolf, 2006; Andreu et al., 2011). The effect of postures used to manipulate the standard or Right Brush on injury prevention or enhancement still needs to be assessed. Further studies using motion analysis systems are needed to further elucidate the effectiveness of handle design and wrist position on preventing OOS. 5. Conclusion Studies have shown the sustained exertion, forceful hand-wrist tasks and repetitive workload with the hand in a posture of a contracted grasping position are the most common risk factors that produce WSMDs-UL such as CTS, trigger finger, and de Quervain's disease (Barr et al., 2004; Bureau of Labor and Statistics, 2004; Laoopugsin and Laoopugsin, 2012; Petit et al., 2015). The notion that any occupational tool that appears to decrease prolonged grip force/muscle activity will potentially decrease the chance of developing “occupational over use syndromes' and WMSDs is not substantiated by the results of this study. If prevention of WMSDsUL is the primary goal, our results show that the right angle handle type has no added ergonomic benefit over a standard handle type in preventing WMSDs-UL especially hand “occupational overuse syndromes.” Our results further suggest that individuals have a preferred technique that they use and changing the shape of the brush handle has no effect on it. Therefore, it is probably more
Fig. 14. aec: The three most used handle positions for individuals using the Right Brush®. Fig. 14a demonstrates the brush designer proposed position where the wrist is in neutral and hand grips the handle like holding a pistol. Fig. 14b shows a similar position but the individual's wrist is slightly extended and radial deviated. Fig. 14c was a position that was commonly used by many painters. Observe the grip on the handle, wrist and fingers held in neutral.
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important that clinicians educate their patients in proper ergonomic techniques than just providing them with a tool that is purported to decrease WSMDs UL when injury prevention is the goal. 5.1. Limitations In this study we did not systematically investigate upper limb posture, hand and wrist position or the actual arm kinematics used by the subjects when painting; we just casually observed upper limb postures/positions and documented the time that a participant changed their grip or appeared to make changes in how they were painting. Conclusions, based on these aspects, are therefore purely speculative and based on the current literature. Acknowledgments This project was supported in part by the Graduate Programs Fund, College of Human Science and Services, University of Rhode Island. The authors thank Jennifer Elias, Emily Holt, Laura Johnson, Sarah Simeone, and Molly Smith for their dedication and proficiency in data collection. References Andreu, J.L., Oton, T., Sanz, J., 2011. Hand Pain other than carpal tunnel syndrome (CTS): the role of occupational factors. Best Pract. Res. Clin. Rheumatol. 25, 31e42. Aptel, M., Aublet-Cuvellier, A., Cnockaert, J.C., 2002. Work-related musculoskeletal disorders of the upper limb. Joint Bone Spine 69, 546e555. Barr, A.E., Barbe, M.F., Clark, B.D., 2004. Work related musculoskeletal disorders of the hand and wrist: epidemiology, pathophysiology, and sensorimotor changes. J. Orthop. Sports Phys. Ther. 34 (10), 610e627. Biometrics Ltd. http://www.biometricsltd.com/filters.htm, (Accessed 11 November 2014). Bongers, P.M., Ijmker, S., van den Heuvel, S., Blatter, B.M., 2006. Epidemiology of work related neck and upper limb problems: psychosocial and personal risk factors (Part 1) and effective interventions from a bio behavioral perspective (Part II). J. Occup. Rehabil. 16, 272e295. Bureau of Labor and Statistics, 2004. In: Lost-worktime Injuries and Illnesses: Characteristics and Resulting Time Away from Work, vols. 9e10, 27, p. 28, 2005;USDL 05-2312, (Accessed September 2012). Carey, E.J., Gallwey, T.J., 2005. Wrist discomfort levels for combined movements at constant force and repetition rate. Ergonomics 48 (2), 171e186. Colombini, D., Occhipinti, E., 2006. Preventing upper limb work-related musculoskeletal disorders (UL-WMSDS): new approaches in job (re)design and current trends in standardization. Appl. Ergon. 37, 441e450. Dale, A.M., Harris-Adamson, C., Rempel, D., Gerr, F., Hegmann, K., Silverstein, B., et al., 2013. Prevalence and incidence of carpal tunnel syndrome in US working populations: pooled analysis of six prospected studies. Scand. J. Work Environ. Health 39, 495e505. Duke, K., Mirka, G., Sommerich, C., 2004. Productivity and ergonomic investigation of bent handle pliers. Hum. Factors 46 (2), 234e243. European Agency for Safety and Health at Work (homepage on the internet): Facts: Work-related neck and upper limb disorders. (https://osha.europa.eu/en/ publications/fact sheets/72). (Accessed March 2014). Fagarasanu, M., Kumar, S., Narayan, Y., 2004. Measurement of angular wrist neutral zone and forearm muscle activity. Clin. Biomech. 19, 671e677. Feuerstein, M., Miller, V.L., Burrell, L.M., Berger, R., 1998. Occupational upper
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extremity disorders in the federal workforce: prevalence, health care expenditures, and patterns of work disability. J. Occup. Environ. Med. 40 (6), 546e555. Finneran, A., O'Sullivan, L., 2013. Effects of grip type and wrist posture on forearm EMG activity, endurance time and movement accuracy. Int. J. Indus. Ergon. 43 (1), 91e99. Fischer, S.L., Wells, R.P., Dickerson, C.R., 2009. The effect of added degrees of freedom and handle type on upper limb muscle activity during simulated hand tool use. Ergonomics 52 (1), 25e35. Fung, B.K.K., Chan, Y., Lam, L.Y., Cheung, S.Y., Choy, N.K., Chu, K.W., et al., 2007. Study of wrist posture, loading and repetitive motion as risk factors for developing carpal tunnel syndrome. Hand Surg. 12 (1), 13e18. Gallagher, S., Pollard, J., Porter, W.L., 2011. Electromyograpy of the thigh muscles during lifting tasks in kneeling and squatting postures. Ergonomics 54 (1), 91e102. Hamre, H.J., Kiene, H., Kienle, G.S., 2009. Clinical research in anthropomorphic medicine. Altern. Ther. Health Med. 15 (6), 52e55. Koningsveld, E.A.P., Dul, J., Van Rhijn, G.W., Vink, P., 2005. Enhancing the impact of ergonomic interventions. Ergonomics 48 (5), 559e580. Laoopugsin, N., Laoopugsin, S., 2012. The study of work behaviors and risks for occupational overuse syndrome. Hand Surg. 17 (2), 205e212. Matern, U., Eichenlaub, M., Waller, P., Ruckauer, K., 1999. MIS instruments: an experimental comparison of various ergonomic handles and their design. Surg. Endosc. 1999 (13), 756e762. Mathiassen, S.E., Winkel, J., Hagg, G.M., 1995. Normalization of surface EMG amplitude from upper trapezius muscle in ergonomic studies - a review. J. Electromyogr. Kinesiol. 5, 197e226. Mell, A.G., Friedman, M.A., Hughes, R.E., Carpenter, J.E., 2006. Shoulder muscle activity increases with wrist splint use during a simulated upper-extremity work task. Am. J. Occup. Ther. 60 (3), 320e326. National Institute of Occupational Safety & Health, 1997. In: Musculoskeletal Disorders and Workplace Factors: a Critical Review of Epidemiologic Evidence for Work-related Musculoskeletal Disorders of the Neck, Upper Extremity, and Low Back, vols. 97e141, pp. 243e310 (Accessed February 2012). Nicoletti, S., Consonni, D., Carino, M., Leone, G., Trani, G., Battevi, N., et al., 2008. Upper limb work-related musculoskeletal disorders (UL-WMADs): a retrospective cohort study in three large factories of the upholstered furniture industry. Med. Lav. 99 (4), 281e296. Palmer, K.T., 2011. Carpal tunnel syndrome: the role of occupational factors. Best Pract. Clin. Rheumatol. 25, 15e29. Petit, A., Ha, C., Bodin, J., Rigouin, P., Descatha, A., Brunet, R., Goldberg, M., Roquelaure, Y., 2015. Risk factors for carpal tunnel syndrome related to the work organization: a prospective surveillance study in a large working population. Appl. Ergon. 47, 1e10. Portney, L.G., Watkins, M.P., 2000. Foundations of Clinical Research: Applications to Practice, second ed. Prentice-Hall, New Jersey. Pullman, S.L., Goodin, D.S., Marquinez, A.I., Tabbal, S., Rubin, M., 2000. Clinical utility of surface EMG: report of the therapeutics and technology assessment subcommittee of the American academy of neurology. Neurology 55 (2), 171e177. Roman-Liu, D., Bartuzi, P., 2013. The influence of wrist posture on the time and frequency EMG signal measures of forearm muscles. Gait Posture 37, 340e344. Roman-Liu, D., Grabarek, I., Bartuzi, P., Choromanski, W., 2013. The influence of mental load on muscle tension. Ergonomics 56 (7), 1125e1133. Ryzewicz, M., Wolf, J.M., 2006. Trigger digits: principles, management and complications. J. Hand Surg. 31A, 135e146. Szeto, G.P.Y., Ng, J.K.F., 2000. A comparison of wrist posture and forearm muscle activities while using an alternative keyboard and a standard keyboard. J. Occup. Rehabil. 10 (3), 189e197. The Right Brush http://www.therightbrush.com, cited November 11, 2013, author, Wholey, M. Thomsen, J.F., Mikkelsen, S., Andersen, J.H., Fallentin, N., Loft, I.P., Frost, P., et al., 2007. Risk factors for hand-wrist disorders in repetitive work. J. Occup. Environ. Med. 64, 527e533. Young, J.G., Trudeau, M.B., Odell, D., Marinelli, K., Dennerlein, J.T., 2013. Wrist and shoulder posture and muscle activity during touch-screen tablet use: effects of usage configuration, tablet type, and interacting hand. Work 45 (1), 59e71.
Contents lists available at ScienceDirect
International Journal of Industrial Ergonomics journal homepage: www.elsevier.com/locate/ergon
Ergonomic comparison between a ‘right angle’ handle style and standard style paint brush: An electromyographic analysis James Agostinucci*, John McLinden Physical Therapy Department, University of Rhode Island, 25 West Independence Way, Kingston, RI, USA
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 March 2015 Received in revised form 24 May 2016 Accepted 24 September 2016
Background: Epidemiologic studies have consistently demonstrated a strong positive association between repetition and “occupational overuse syndromes” (OOS). The repetitive nature of painting then can predispose many people to these disorders. Objective: The purpose of this study was to conduct an electromyographic analysis (EMG) comparing a right angle handle paint applicator with a commonly used, equal quality standard handle paint brush. Method: A randomized cross over repeated measures design was implemented where 30 volunteers were randomly given a paint brush handle type while muscle activity (EMG) was recorded from eight upper limb muscles groups. Subjects were their own controls returning within one week to perform the same painting activity with the other paint brush handle type. ANOVA with repeated measures was used to analyze the EMG data among muscles between the two painting trials. Results: EMG analysis revealed that there was no difference in EMG activity or median frequency between the two types of paint brush handles in the eight muscles studied (p > 0.05). Conclusion: A right angle handle has no added ergonomic advantage in modifying muscle activity or decreasing muscle fatigue over a commonly used standard handle paint brush in people without injury. It was suggested that the right angle style brush may not prevent OOSs from occurring, although there still could be a decrease risk of injury based on the posture used when gripping the brush handle. It must be emphasized, however, that this study's results cannot be extrapolated to people who already have an OOS and need a device to prevent further injury and pain. Further study is needed. © 2016 Elsevier B.V. All rights reserved.
Keywords: Occupational overuse syndromes Repetitive strain injury Work-related musculoskeletal disorders Carpal tunnel syndrome Trigger finger De Quervain's disease
1. Introduction The principle behind ergonomic tools is to increase productivity by reducing fatigue, increasing comfort and lowering the risk of injury. Ergonomically designed hand-held tools attempt to increase biomechanical efficiency by manipulating hand and wrist position (Koningsveld et al., 2005; Dale et al., 2013). Wrist and hand positions have a significant impact on muscle groups recruited (Carey and Gallwey, 2005; Mell et al., 2006), discomfort, and on the possibility of causing trauma (Feuerstein et al., 1998; Barr et al., 2004; Bureau of Labor and Statistics, 2004; Duke et al., 2004; Fung et al., 2007; Fischer et al., 2009) therefore ergonomic designs have a significant degree of necessity. Epidemiologic studies have shown a significant positive correlation between Carpal Tunnel Syndrome (CTS) and certain risk factors such as repetition, force, wrist
* Corresponding author. E-mail address: [email protected] (J. Agostinucci). http://dx.doi.org/10.1016/j.ergon.2016.09.008 0169-8141/© 2016 Elsevier B.V. All rights reserved.
position (Barr et al., 2004; Bureau of Labor and Statistics, 2004) and increased muscle activity (Fagarasanu et al (2004; Finneran and O'Sullivan, 2013; Roman-Liu and Bartuzi, 2013)., especially when there is a combination of these risk factors. Repetitive motion musculoskeletal disorders (RMD's), such as CTS, Lateral Epicondylitis (LE) and other enthesopathies of the upper extremity associated with poor wrist position, have been shown to significantly increase the numbers of missed work days (Barr et al., 2004; Dale et al., 2013; Petit et al., 2015). According to the Bureau of Labor and Statistics (2004), an average of 20 work-days are missed each year per instance due to repetitive motion wrist injuries. Health care costs for federal workers over the course of a one year study for these types of claims were $12, 228, 755,228,755 with an average individual cost of $2849 and the average indemnity cost was approximately $4700 (Feuerstein et al., 1998). These findings indicate that while upper extremity disorders represent a relatively small percentage of all workers' compensation cases, the health care and indemnity costs are considerable (Feuerstein et al., 1998).
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Painting has an inherent risk for developing “occupational overuse syndromes” (OOS) due to the repetitive nature of the task, and epidemiologic studies have consistently demonstrated a strong positive association between repetition and RMD's (Thomsen et al., 2007; National Institute of Occupational Safety & Health, 2012). Decreasing the risks associated with painting has the potential to impact a significant portion of the population. The International Union of Painters and Allied Tradesmen (IUPAT) is comprised of 140,000 reported members within the United States and Canada, who are predominantly employed in the construction industry (Hamre et al., 2009). Painting is also a common do-it-yourself home improvement task. These factors increase the potential positive impact of an ergonomically designed painting tool. Standard paint brush handle types require a wrist position that have been shown to increase in the myoelectric activity of muscles linked to repetitive strain injury (Duke et al., 2004; Fagarasanu et al., 2004; Finneran and O'Sullivan, 2013; Roman-Liu and Bartuzi, 2013). The more glaring effect of handle type on wrist position was excessive ulnar deviation (Matern et al., 1999; Duke et al., 2004). Ulnar deviation was shown to produce a significantly greater amount of muscle activity compared to more neutral wrist positions (Fagarasanu et al., 2004; Roman-Liu and Bartuzi, 2013). In the case of an axial or “screwdriver” type handle, the handle is in line with the long axis of the forearm resulting in increased ulnar deviation, (Matern et al., 1999; Koningsveld et al., 2005; Mell et al., 2006; Fischer et al., 2009; Hamre et al., 2009). Therefore, any ergonomic device that promotes the wrist neutral position, theoretically, would be superior in preventing injuries. There are many ergonomically designed hand-held paintbrushes currently available commercially. One ergonomic design employs a right-angle handle position. A more neutral wrist position can be maintained with a bent handle tool, the axis of which is perpendicular to the long axis of the limb (Duke et al., 2004). Standard paint brushes are typically held in the same position as other screwdriver-type handles, while “right angle” paint brushes employ a bent handle, which encourages a neutral wrist position and can potentially recruit muscle groups less prone to fatigue. Since Finneran and O'Sullivan (2013) and others (Young et. al. 2013; Szeto and Ng, 2000) showed grip type had a highly significant effect on forearm muscle activity (EMG) of all the muscles they tested, assessing muscle activity through surface EMG may be an easy and effective way of evaluating the ergonomic value between the two brush types. Lastly, the use of axial type handles require a more precision grip that recruits the smaller more fatigable hand muscles. Higher precision requirements often slow tasks and reduces output. The additional time it takes to complete a task while in a stressed position further increases the probability of obtaining an OOS (Finneran and O'Sullivan, 2013). Comparing muscle activity from hand, forearm and other upper extremity muscles will provide important information to show which muscles are more actively involved between the two brush handle types. The purpose of this pilot study was to evaluate the muscle activity (EMG) of upper limb muscles associated with the standard hand-held paint brush and a commercially available “right angle” paint brush, called the ‘Right Brush®’, to make a comparison between the two. The ‘Right Brush®’ claims to decrease the probability of acquiring RMD's and other related disorders by promoting use of larger proximal muscles that are less prone to fatigue and prevent inappropriate hand/wrist positions (Wholey, The Right Brush®, 2013). While a particular handle type may appear more ergonomically correct, it still may result in similar musculoskeletal abnormalities (Duke et al., 2004). Results will evaluate whether the design of the ‘Right Brush®’ is a viable ergonomic alternative.
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2. Materials and methods 2.1. Subjects Thirty healthy volunteers were recruited using flyers placed in various stores that sell painting supplies, around the local community, and by word of mouth. Inclusion criteria for this study were participants were between the ages of 18e65, had some previous painting experience, and had no history of musculoskeletal or neuromuscular disorders of the dominant upper limb. All participants read and signed an informed consent form approved by the University of Rhode Island Institutional Review Board and completed a general health questionnaire. The study took place in a well ventilated room to ensure safety of the participants and researchers. 2.2. Materials A 40 70 wooden structure was constructed for subjects to paint (Figs. 1 and 2) This structure simulated commonly painted areas of a house including trim, a bookshelf and fixtures. The structure was used a total of 15 times, receiving 30 coats of paint on each side, after which it was replaced with an identical structure. Areas of the structure were labeled one through six, with areas one through four located on the front and areas five and six located on the back (Figs. 1 and 2). This was done to standardize location of painting during electromyographic recordings for statistical analysis. Acrylic based paints were used for safety purposes. Acrylic based paints give off less fumes and can be cleaned with regular soap and warm water. Two different neutral paint colors were used to differentiate between participant's trials. Paint brushes used included a standard paint brush (Fig. 3) with the traditional, screwdriver type handle and the newly designed ‘Right Brush®’ (Fig. 4) with a right-angled handle encouraging a right angle grip. Both brushes were of similar weights and 2 ½ inches wide with polyester-nylon bristles. Both paint brushes were made by ArrowWorthy®. EMG: An 8- channel wireless blue-tooth electromyograph (EMG) (PS 850 Data Log, Biometrics Ltd., UK) was used to record upper limb muscle activity. Bipolar AgeAgCl surface electrodes
Fig. 1. Structure front with numbers.
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Fig. 2. Structure back with numbers.
Fig. 3. Standard brush.
Fig. 5. EMG attachment on participant.
of 30 min (seven total recordings). Each recording lasted 10 s. The myoelectric signals were digitized at 1000 Hz at a bandwidth of 20e450 Hz and stored on a designated computer for future analysis. The EMG's amplifier had an input impedance of 1 MΏ (4730 pf), a common Mode Rejection ratio of 96 dB @ 50 Hz and a signal to noise ratio of <1 m V r.m.s. 2.3. Experimental procedure
Fig. 4. The right Brush®.
were placed on the skin over the abductor pollicus brevis (APB), flexor carpi radialis (FCR) and extensor digitorum (ED), biceps and triceps, anterior deltoid muscle, upper trapezius, and the clavicular portion of the pectoral major muscle of the dominant arm. It must be emphasized that surface EMG record myoelectric potentials from all the muscles within the territory of the surface electrode and the specific muscles were mentioned for only description purposes to identify the exact location that the EMG electrodes were placed. (Pullman et al., 2000). The muscle groups lying under the electrodes were chosen according to the muscle actions required of the upper extremity during painting activities, including, grip, wrist stability, activity at the elbow, and shoulder flexion. The ground electrode was placed on the lateral malleolus of the ankle contralateral to each participant's dominant hand. A belt was used to secure the DataLog base to the participant's waist and pre-wrap straps, to allow free movement of the upper extremity during painting (Fig. 5). EMG recordings were taken at initiation of painting (baseline) and at 5 min intervals for duration
The experiment began by randomly giving the participant the ‘Right Brush®’ or the standard paint brush with an open gallon of paint. Painters were allowed to hold the brush in any way they deemed comfortable throughout the trial. Once the EMG electrodes, wires and DataLog base were secured, participants were instructed to begin practice painting motions until they felt comfortable using the paintbrush. Participants were instructed to start painting anywhere on the structure and their goal was to paint both sides. Participants were allowed to paint freely for 5 min, at which time they were directed to the numbered areas on the structure (Figs. 1 and 2), where they were instructed to paint for a minimum of 10 s. EMG recordings were taken during this 10 s interval. After the 10 s participants were instructed to continue painting freely. This process continued until all 6 numbered areas were painted. The numbered areas were painted in the same order and at the same point in every trial to ensure consistency of EMG data for statistical analysis. The participants were also observed to ensure that EMG recording were taken only during painting and not when the subject was performing other painting-related activities (i.e. dipping the brush into the paint can). Upon completion of the task, participants were asked to rate their subjective fatigue level from the upper limb they used in painting with special attention to the areas where surface electrodes were placed for each of the brush handle types. Rating were conducted on a visual analog chart (VAS) (Fig. 6). Participants returned within one to seven days to complete the same experimental procedure using the alternate brush. Each participant therefore painted the wooden structure twice using a different brush each time.
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Table 1 Participant demographics. Number of Participants
Fig. 6. Fatigue visual analog scale.
2.4. EMG analysis EMG data was downloaded to the designated computer and was analyzed using the Biometrics DataLOG analysis software. To provide a way of reducing the amount of error arising from natural variance between individuals each participant severed as their own controls In addition, since EMG values depend closely on personal characteristics, measuring their values across individuals and comparing them between tests require normalization to some type of reference. Customarily the average of 1e4 maximum voluntary contractions is used as the reference value (Mathiassen et al., 1995; Gallagher et al., 2011). In this study, having subjects maximally contract 1e4 times for each of the eight muscle groups was fatiguing and not practical. Therefore we chose to normalize EMG data by having the subject paint for 10 s before the 1st trial EMG was recorded and use this initial EMG recording as the reference that all other EMG trials were compared to for that EMG session (Roman-Liu et al., 2013). Care was taken to assure that the reference EMGs were recorded during painting activities that were similar among painting sessions and subjects. Two EMG analyses were performed from the raw signals; area under the curve and Median frequency (MF). For the area under the curve analysis, the raw EMG signal was full wave rectified, filtered at 20 to 500 KHz and integrated (area under the curve) for each of the six 10 s recording, for each muscle, for each brush handle type.” Median frequency was calculated from the same raw EMG signals using the “Biometrics DataLOG analysis software” median frequency filter. A sliding window technique with a step size of 500 samples and a window size of 10,000 samples. Refer to www.biometricsltd.com/filters.htm for detailed information about this methodology. MF values were plotted for each muscle. 2.5. Statistical analysis Statistical analysis used the ratios of the EMGs (trial EMG/ reference EMG) and any change in these ratios determined its significance. Each 10 s recording interval was defined as one trial. There were 6 trials taken within a 30 min painting activity. OneWay ANOVA's with two repeated measures (brush type, trials) was used to compare each muscle's myoelectric activity between the two brush types. The subjective fatigue level that was gathered from the VAS was analyzed using the signed rank test to determine if there was a difference between the paint brushes. A non-parametric test were was used because the data were not normally distributed. 3. Results Five participants were omitted from data analysis due to premature terminating the experiment (2 participants) or had unstable EMG recordings (3 participants). Of the 25 subjects that completed the study, there were 10 males and 15 females, 23 righthand dominant and two left-hand dominant, 24 novice painters and one a professional painter. Refer to Table 1 one for participant demographics.
Age Range 18e30 30e45 45e65 Gender Male Female Dominant Hand Left Hand Right Hand
21 1 3 10 15 2 23
3.1. EMG and median frequency data Figs. 7 and 8 show a representation of the mean integrated EMG from the thenar and dorsal forearm muscle groups. As can be observed from the graph, there was not any difference in muscle activity between the two brush handle types. All other muscle groups showed similar non-significant results. Figs. 9 and 10 show the mean median frequency from the triceps and upper trapezius muscle groups in all 25 subjects. As in EMG integrated data, the differences between the median frequencies between the two handle types were also similar and insignificant for all seven muscle groups. The only exception in median frequency data was from the APB muscle (Fig. 11). Median frequencies from this muscle were very stable over time and. did not decline as it did for the other six muscle groups. Since the APB did not show the same fatigue characteristics as the other muscle groups it was concluded that the larger extrinsic hand muscles were more important in holding onto the paint brush handles. Differences between the two handle types for this muscle were again not significant. 3.2. Questionnaire data Participants rated the ‘Right Brush®’ generally less fatiguing (Figs. 12 and 13), (p < 0.05). In it noteworthy to mention, that the subjective fatigue ratings from many individuals did not correspond with their MF data. These responses may be related to the phenomenon known as the Hawthorne effect, where people perform or rate items as superior merely because they expect it to be better (Portney and Watkins, 2000). This interpretation, however, is purely speculative. It is quite possible participant's subjective fatigue level increase legitimately and our method of assessment (MF) was inadequate. Interestingly, the one subject who identified themselves as a professional painter (subject 19 in Fig. 13) rated the ‘Right Brush® substantially more fatiguing. 4. Discussion Work-related musculoskeletal disorders (WMSDs) have become one main focus in occupational disease prevention (Laoopugsin and Laoopugsin, 2012). In particular, upper limb WMSDs (WMSDs-UL) are today the commonest forms of occupational disease in many parts of the industrialized world (Aptel et al., 2002; Colombini and Occhipinti, 2006; Nicoletti et al., 2008). Numerous epidemiological studies conducted during the last 20 years have provided data supporting causal relationships between exposure to work-related risk factors and the development of WMSDs-UL. Barr et al. (2004), Bongers et al. (2006) and Laoopugsin and Laoopugsin (2012) showed that prolonged, highly repetitive and forceful hand-wrist tasks are the most common factors causing WMSDs such as carpal tunnel syndrome (CTS). From the conclusions of these studies it
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Fig. 7. Thenar Muscle Activity. Plots represent the amount of muscle activity for each time interval during the experiment for the two brushes. Each point represents the average ratios in millivolts (mV) from the integrated EMG (IEMG) of all subjects over a 10 s period. (p > 0.05). Standard deviations are also shown.
Fig. 8. Forearm Extensor Muscle Activity. Plots represent the amount of muscle activity for each time interval during the experiment for the two brushes. Each point represents the average ratios in millivolts (mV) from the integrated EMG (IEMG) of all subjects over a 10 s period. (p > 0.05). Standard deviations are also shown.
Fig. 9. Posterior arm muscle group median frequency (MF). Plots represent the MFs for each time interval during the experiment for the two brushes. Each point represents the average ratios in Hertz (HZ) from the EMG power spectral analysis (MF interval/MF baseline). (p > 0.05). Standard deviations are also shown.
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Fig. 10. Upper trapezius median frequency (MF). Plots represent the MFs for each time interval during the experiment for the two brushes. Each point represents the average ratios in Hertz (Hz) from the EMG power spectral analysis (MF interval/MF baseline).
MF interval/ MF baseline (Hz)
2.0
1.5 Right Brush Standard Brush 1.0
0.5
0.0 0.1
5
10
15
Time (minutes)
20
25
30
Fig. 11. Thenar muscle group median frequency (MF). Plots represent the MFs for each time interval during the experiment for the two brushes. Each point represents the average ratios in Hertz (Hz) from the EMG power spectral analysis (MF interval/MF baseline).
Fig. 12. Subjective mean fatigue level. Average visual analog scale determinations from 25 subjects. Standard deviations are also shown. Subjects rated the ‘Right Brush® slightly less fatiguing (p < 0.05).
was recommended more attention be brought to hand function of employees in the work place since today WMSDs-UL are the most common forms of occupational disease accountings for more than 45% of all occupational diseases (European Agency for Safety and Health at work, 2014). In this study we used ‘painting’ as the task to study upper extremity muscle activity and fatigue. Painting encompasses many risk factors that lead to WMSDs-UL including CTS (Palmer, 2011; Petit et al., 2015). It is a prolonged activity, is repetitive, requires isometric and isokinetic muscle contractions of all upper limb muscles including the hand, and may place the wrist in several distinct positions that have been shown to increase the probability of developing WMSDs-UL (Carey and Gallwey, 2005). The main findings of this study showed that the myoelectric activity required to hold and paint with the ‘Right Brush®’ was no different from that of a standard brush. This suggests that a “right angle handle” paint brush handle has no ergonomic benefit over a standard paint brush handle in lowering muscle activity or
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Fig. 13. Scatter plot of Individual fatigue ratings ratios. Participants gave their subjective fatigue levels by choosing a number from 1 to 10 on a visual analog scale where 1 was no fatigue and 10 was sever fatigue (exhausting). Y axis represents the ratio of the subject fatigue ratings from Right brush/standard brush. Response of 1 indicates no difference in fatigue levels between the brushes. Values under 1 represents less fatigue when using the ‘Right Brush® and levels over 1 indicate that the standard brush was less fatiguing. Subjects rated the ‘Right Brush® less fatiguing (p < 0.05).
decreasing fatigue. The muscle activity used to hold onto the paint brush handle as well as the painting strokes (movement) of the other upper extremity muscles are therefore not determined by the handle type but rather by other aspects specific to the individual painter. This was demonstrated during the experiment. As time progressed, participants were observed casually changing grips (Fig. 14aec) and altering their strokes probably adjusting to fatiguing muscles. These compensatory patterns are (likely) utilized to adjust to muscle fatigue while attempting to maintain appropriate forces required to continue painting effectively and comfortably. Figs. 10 and 11 demonstrate these phenomena in the triceps and upper trapezius muscles. As can be seen from the figures, the median frequency (MF) appears to decrease from the start of painting to approximately 20 min as painting progresses. This is a normal response to fatigue. However, around 20e25 min, a large increase in MF occurred. Coincidentally, it was noticed in many participants that at the time of the MF increase a grip/position change occurred at approximately the same time take place resulting in a change in their overall painting technique. This MF change was also seen in the other muscles recorded from except the abductor pollicis brevis, which showed a more stable fatigue level (Fig. 10.). This study's protocol had participants paint with one type of brush handle and then returning one to seven days later and painting again using the other brush (within participant design). The paint handle, therefore, was the only variable that changed. Participants were carefully
guided through the painting process so that each muscle was recorded while the subject painted the same part of the jig. This insured a consistent EMG comparison between trials. Referring to all the EMG Figs. 7e11 it can be seen that the traces between each muscle are almost identical even though the second day of painting was three to seven days later. These results strongly suggest that participants use the same painting technique whether they used a right angle handle or a standard handle paint handle. The results of this study suggest that if the goal is to prevent injury, the postures used during the task may have more impact than the tool used, regardless of the tool's face validity. When considering strategies to decrease injury, emphasis should be placed on correct body mechanics principles so that the physical activity is performed properly in addition to tool design considerations. This proposition is in accordance with the findings of Fagarasanu et al. (2004) and Finneran and O'Sullivan (2013) who showed that the neutral wrist position significantly decreases muscle activity. These results suggest the neutral wrist posture will reduce the risk of injuries. Therefore, based on our finding, prescribing only an ergonomically designed tool without proper instruction may have no beneficial effect. It should be emphasized that we did not directly measure the effect that hand/wrist posture had on inducing or preventing injury. Studies have shown that certain grip/wrist positions are directly related to the increased prevalence of CTS (Laoopugsin and Laoopugsin (2012), de Quervain's disease and trigger finger (Ryzewicz and Wolf, 2006; Andreu et al., 2011). The effect of postures used to manipulate the standard or Right Brush on injury prevention or enhancement still needs to be assessed. Further studies using motion analysis systems are needed to further elucidate the effectiveness of handle design and wrist position on preventing OOS. 5. Conclusion Studies have shown the sustained exertion, forceful hand-wrist tasks and repetitive workload with the hand in a posture of a contracted grasping position are the most common risk factors that produce WSMDs-UL such as CTS, trigger finger, and de Quervain's disease (Barr et al., 2004; Bureau of Labor and Statistics, 2004; Laoopugsin and Laoopugsin, 2012; Petit et al., 2015). The notion that any occupational tool that appears to decrease prolonged grip force/muscle activity will potentially decrease the chance of developing “occupational over use syndromes' and WMSDs is not substantiated by the results of this study. If prevention of WMSDsUL is the primary goal, our results show that the right angle handle type has no added ergonomic benefit over a standard handle type in preventing WMSDs-UL especially hand “occupational overuse syndromes.” Our results further suggest that individuals have a preferred technique that they use and changing the shape of the brush handle has no effect on it. Therefore, it is probably more
Fig. 14. aec: The three most used handle positions for individuals using the Right Brush®. Fig. 14a demonstrates the brush designer proposed position where the wrist is in neutral and hand grips the handle like holding a pistol. Fig. 14b shows a similar position but the individual's wrist is slightly extended and radial deviated. Fig. 14c was a position that was commonly used by many painters. Observe the grip on the handle, wrist and fingers held in neutral.
J. Agostinucci, J. McLinden / International Journal of Industrial Ergonomics 56 (2016) 130e137
important that clinicians educate their patients in proper ergonomic techniques than just providing them with a tool that is purported to decrease WSMDs UL when injury prevention is the goal. 5.1. Limitations In this study we did not systematically investigate upper limb posture, hand and wrist position or the actual arm kinematics used by the subjects when painting; we just casually observed upper limb postures/positions and documented the time that a participant changed their grip or appeared to make changes in how they were painting. Conclusions, based on these aspects, are therefore purely speculative and based on the current literature. Acknowledgments This project was supported in part by the Graduate Programs Fund, College of Human Science and Services, University of Rhode Island. The authors thank Jennifer Elias, Emily Holt, Laura Johnson, Sarah Simeone, and Molly Smith for their dedication and proficiency in data collection. References Andreu, J.L., Oton, T., Sanz, J., 2011. Hand Pain other than carpal tunnel syndrome (CTS): the role of occupational factors. Best Pract. Res. Clin. Rheumatol. 25, 31e42. Aptel, M., Aublet-Cuvellier, A., Cnockaert, J.C., 2002. Work-related musculoskeletal disorders of the upper limb. Joint Bone Spine 69, 546e555. Barr, A.E., Barbe, M.F., Clark, B.D., 2004. Work related musculoskeletal disorders of the hand and wrist: epidemiology, pathophysiology, and sensorimotor changes. J. Orthop. Sports Phys. Ther. 34 (10), 610e627. Biometrics Ltd. http://www.biometricsltd.com/filters.htm, (Accessed 11 November 2014). Bongers, P.M., Ijmker, S., van den Heuvel, S., Blatter, B.M., 2006. Epidemiology of work related neck and upper limb problems: psychosocial and personal risk factors (Part 1) and effective interventions from a bio behavioral perspective (Part II). J. Occup. Rehabil. 16, 272e295. Bureau of Labor and Statistics, 2004. In: Lost-worktime Injuries and Illnesses: Characteristics and Resulting Time Away from Work, vols. 9e10, 27, p. 28, 2005;USDL 05-2312, (Accessed September 2012). Carey, E.J., Gallwey, T.J., 2005. Wrist discomfort levels for combined movements at constant force and repetition rate. Ergonomics 48 (2), 171e186. Colombini, D., Occhipinti, E., 2006. Preventing upper limb work-related musculoskeletal disorders (UL-WMSDS): new approaches in job (re)design and current trends in standardization. Appl. Ergon. 37, 441e450. Dale, A.M., Harris-Adamson, C., Rempel, D., Gerr, F., Hegmann, K., Silverstein, B., et al., 2013. Prevalence and incidence of carpal tunnel syndrome in US working populations: pooled analysis of six prospected studies. Scand. J. Work Environ. Health 39, 495e505. Duke, K., Mirka, G., Sommerich, C., 2004. Productivity and ergonomic investigation of bent handle pliers. Hum. Factors 46 (2), 234e243. European Agency for Safety and Health at Work (homepage on the internet): Facts: Work-related neck and upper limb disorders. (https://osha.europa.eu/en/ publications/fact sheets/72). (Accessed March 2014). Fagarasanu, M., Kumar, S., Narayan, Y., 2004. Measurement of angular wrist neutral zone and forearm muscle activity. Clin. Biomech. 19, 671e677. Feuerstein, M., Miller, V.L., Burrell, L.M., Berger, R., 1998. Occupational upper
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