Effects of BMI and task parameters on joint angles during simulated small parts assembly

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International Journal of Industrial Ergonomics 43 (2013) 417e424

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International Journal of Industrial Ergonomics

journal homepage: www.elsevier .com/locate/ergon

Effects of BMI and task parameters on joint angles during simulatedsmall parts assembly

Michael A. Hamilton a,*, Lesley Strawderman a, Kari Babski-Reeves a, Brendon Hale b

aDepartment of Industrial & Systems Engineering, Mississippi State University, P.O. Box 9542 MSU, MS 39762, USAbDepartment of Kinesiology, Mississippi State University, P.O. Box 6186 MSU, MS 3976, USA

a r t i c l e i n f o

Article history:Received 16 February 2012Received in revised form26 March 2013Accepted 14 August 2013Available online 1 October 2013

Keywords:ObeseFunctional reachWorkstationJoint anglesObesityGender differences

* Corresponding author. Tel.: þ1 540 413 6153.E-mail address: [email protected] (M.A

0169-8141/$ e see front matter � 2013 Elsevier B.V.http://dx.doi.org/10.1016/j.ergon.2013.08.003

a b s t r a c t

Functional limitations of persons classified into different obesity categories were evaluated while per-forming a simulated small parts assembly tasks. Joint angles (measured using electro-goniometers) andmaximum forward function reach (MFFR) were used to quantify function limitations, and tasks werecompleted on three workstations designed for the 5th, 50th, and 95th percentile workers based onanthropometric data tables. Results revealed that BMI category did not significantly affect measured jointangles. Results also indicated that joint angles when working at the 95th percentile workstationconfiguration were significantly larger than those measured at the 5th percentile workstation configu-ration. Further, obese class 2 and obese class 3 groups MFFRs were significantly shorter than the normalweight group, which was expected. These results imply that workstation design considerations shouldinclude obesity levels, and that work should be placed near the worker and should be elevated to reducepressure on joint angles while working for larger (obese) individuals.Relevance to industry: Obesity is a widespread problem for most leading world nations. In contrast to thecomprehensive literature on obesity, there is very little research on the functional limitations of theobese population. There is a need to obtain a better understanding of the musculoskeletal system of theobese, specifically their functional reach limitation and joint angles while working at a standingworkstation.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

Obesity is an epidemic among most leading world nations,particularly in the United States (Levine et al., 2005; Wearing et al.,2006). In the United States, over 35% of adults are obese (Ogdenet al., 2012). Obesity, as well as occupational morbidity, are risingissues worldwide (Mokdad et al., 2003). In the United States,obesity-related medical expenditures in 2009 reached approxi-mately 147 billion dollars, and have been increasing (Finkelsteinet al., 2009; Levine et al., 2005). In this country alone, obesitycontributes to over nine percent of total medical expenditures(Finkelstein et al., 2009; Khan et al., 2009).

The study of the human work environment has been a long-lasting and challenging problem for researchers (Cimino et al.,2009; Fogliatto and Guimarase, 2004; Nanthavanij, 1996). Theneed for improved workstation design has become apparent,particularly in jobs requiring repetitive motion that are of high risk

. Hamilton).

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for work-related musculoskeletal disorders (WMSDs) (Kumar andKumar, 2008; Hsin-Chieh et al., 2009). In contrast to the compre-hensive literature on obesity and its negative impact on the humanbody, there is very little research on the functional limitations ofthe obese working population (Wearing et al., 2006). Therefore, it isimportant to acquire a better appreciation of the influence ofobesity in the workplace, and the functional limitations that resultfrom excessive fat on the body.

Recognizing the locomotor characteristics related to work tasksis important in the obese population (Das and Sengupta, 1996).Consequently, there is a need to research the effects Body MassIndex (BMI) has on performing work tasks at an assembly work-station. Currently, there appears to be little to no research quanti-fying the effect of different levels of obesity on joint angles andfunctional reach at assembly workstations. However, there arestudies which focus on applied workstation design in the fabrica-tion industries, visual display terminals, and determining the bestworkstation practices specific to certain musculoskeletal disorders.

O’Sullivan and Gallwey (2002) explored the effects of genderand reach distance when performing an assembly task. The pur-pose of the research was to study differences in the elbow and

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Table 1Task sequencing.

Task number Representation

1 Right hand to Work Bin D (Near Reach)2 Left hand to Work Bin B (Near Reach)3 Right hand to Work Bin C (Mid-Reach)4 Left hand to Work Bin A (Mid-Reach)5 Right hand to Work Bin E (Cross Reach)6 Left hand to Work Bin F (Cross Reach)7 Right hand to Work Bin G (Max Reach)8 Left hand to Work Bin G (Max Reach)

M.A. Hamilton et al. / International Journal of Industrial Ergonomics 43 (2013) 417e424418

shoulder flexion angles while performing an assembly task. Theyfound elbow angles of females are larger than those of males, butthe shoulder angles of males are larger than those of females. Duethe difference in the shoulder angle, women are more susceptibleto awkwardwork postures when thework task is farther away fromthe body. The researchers believed understanding this effect willimprove the likelihood of designing better gender specific work-stations (O’Sullivan and Gallwey, 2002).

Singh et al. (2009) investigated the effects of obesity onmaximum frontal reach while standing in an upright position. Thesubjects were asked to extend their arm as far as they could whileleaning forward without losing their balance. The data weremeasured using a yardstick from the center point of their head inthe upright position to the third metacarpal. Results showed thattheir frontal reach was significantly shorter for the obese whencompared to normal weight individuals. If the results are similar ina workstation environment, there could be significant implicationson workstation material placement, especially when consideringthe maximum frontal functional reach (MFFR) of the obeseindividual.

Wearing et al. (2006) explored the current literature on obesityand realized there is a dearth of research on obesity concerning thefunctional limitations caused by obesity. The authors believed thereshould be a better understanding of locomotor characteristics ofthe obese when completing work tasks. This will enhance knowl-edge on the functional limitations and weight bearing load on themusculoskeletal symptoms of the obese.

To date, analyses on locomotor tasks included only normalweight individuals. Sit-to-stand movements are among the fewbiomechanical aspects of the obese that have been studied; none-theless, there is limited documentation regarding work and dailyliving tasks of the obese population (Wearing et al., 2006).

1.1. Research objectives

The objective of this studywas to quantify the effects of personaland task parameters on maximum frontal functional reach (MFFR)

Table 2Demographic data by BMI group and gender.

Normal Overweight

All participantsAge 23 (3.61) 23 (3.50)BMI 23 (0.84) 26 (1.46)Weight (kg) 70.47 (9.25) 78.31 (7.48)Male participantsAge 24 (4.58) 26 (3.00)BMI 23 (1.01) 26 (1.57)Weight (kg) 73.26 (5.30) 84.52(5.93)Female participantsAge 21 (2.52) 21 (0.58)BMI 23 (0.84) 26 (1.70)Weight (kg) 66.22 (9.70) 71.89 (0.96)

and joint angles on the body while performing simulated smallparts assembly. Specifically, this study quantified the effects of theelbow, neck and back angles as a function of BMI classification,gender, and workstation configuration. The specific hypothesesinvestigated included:

1. Joint angles would be affected by BMI classification. As BMIclassification increases in obesity level, joint angles were ex-pected to increase.

2. Joint angles would be affected by workstation configuration.Workstations were designed according to anthropometric di-mensions for the 5th, 50th, and 95th percentile for both gen-ders. As theworkstation dimensions increase, joint angles wereanticipated to increase.

3. The MFFR would be affected by BMI classification, but notgender. As BMI classification increases in obesity level, MFFRwas expected to decrease.

2. Methods

Three independent variables were studied: BMI classification,workstation configuration, and gender. The dependent variablestested were the actual observed angles of the neck (flexion andextension), elbow (flexion and extension), and trunk (flexion,extension, and lateral bending) while completing small partsassemblies. Tasks were completed on three different worksta-tion configurations representing the 5th, 50th, and 95thpercentile worker (based on height). On the workstation surface,work bins were placed strategically across the work area torepresent reach distances that were considered near, mid, cross,and maximum functional reach distances. When creating theassemblies, the participants performed the tasks in a controlledpattern. There were eight unique reach patterns (Table 1), andeach participant performed each pattern three times to createone assembly.

Additionally, each participant’s MFFR was collected to evaluatedifferences in reach limitations among the BMI groups. A mixedfactor experimental design was used to quantify the effects of BMIclassification (5 levels), gender (2 levels), and workstation config-uration (3 levels) on joint angles differences of the elbow, neck, andback, and MFFR. BMI classification and gender were between sub-jects factors, and workstation configuration was a within subjectsfactor. Workstation configuration was randomized to control fororder effects. Tukey pair-wise post-hoc analyses were conducted asneeded on significant findings. All findings were considered sig-nificant at an alpha level of 0.05, and all analyses were completed inSAS 9.2.

Previous research has quantified postural sway in the medial-lateral direction for obese subjects, providing a standard

Obese class 1 Obese class 2 Obese class 3

20 (0.89) 22 (1.10) 25 (8.98)32 (1.31) 38 (1.38) 44 (3.75)

95.82 (9.28) 107.32 (4.94) 134.65 (15.63)

20 (1.15) 22 (1.53) 30 (10.54)32 (1.26) 37 (1.73) 44 (4.97)

103.23 (6.62) 113.40 (1.61) 146.06 (11.85)

20 (0.58) 22 (0.58) 19 (0.00)32 (1.60) 38 (1.22) 44 (3.24)

88.90 (4.73) 103.41 (1.79) 125.34 (14.45)

Table 3Workstation configuration bin locations (values are in cm).

Bin angle location

�60� �40� �20� 0� 20� 40� 60�

5th Male 28.75 39.08 29.33 42.30 29.33 39.08 28.7550th Male 32.50 45.38 35.10 50.30 35.10 45.38 32.5095th Male 35.95 50.03 41.78 57.50 41.78 50.03 35.955th Female 27.15 36.53 28.20 39.80 28.20 36.53 27.1550th Female 30.60 42.30 35.33 49.60 35.33 42.30 30.6095th Female 34.05 47.93 40.80 56.40 40.80 47.93 34.05

M.A. Hamilton et al. / International Journal of Industrial Ergonomics 43 (2013) 417e424 419

deviation of 0.09 (Hue et al., 2007). By using the statistics re-ported by Hue, the required sample size was calculated to be 25participants for the current study. Since two levels of gender andfive levels of obesity were tested, the research sample size was 30participants (15 males and 15 females) to allow for a balancedexperimental design. A stratified sampling procedure, withBMI classification as the stratification variable, was used torecruit participants. Three males and three females withineach of the five BMI classifications were tested. The five BMIclassifications were: Underweight/Normal weight (14.9 kg/m2

< BMI � 24.9 kg/m2), Overweight (25 kg/m2 � BMI � 30 kg/m2),Obese Class 1 (30.1 kg/m2 � BMI � 34.9 kg/m2), Obese Class 2(35 kg/m2 � BMI � 40 kg/m2), and Obese Class 3(BMI > 40 kg/m2). The demographic data for the participants areshown below in (Table 2).

2.1. Workstation configuration

Three workstation configurations were studied based on reachdistances for the 5th, 50th, and 95th percentiles respective ofgender (i.e., a “male” and “female” workstation were constructedand participants completed the task on their gender specificworkstation). A single work surface was used for all workstationconfigurations, though color coding was used to identify male/fe-male reach distances at each percentile.

The height of the workstation was set at 12.7 cm below eachparticipant’s elbow height in accordance with workstation guide-lines for light work (ESA, 2009; NIOSH, 2001). Each subjectcompleted the task (described below) in a designated assemblyarea placed in front of the participant in the center of the worksurface (Fig. 1).

Eight assembly part bins were placed at specific locations thatrepresented near, middle, or maximum distances at various angles.At each percentile (5th, 50th, and 95th) reach distances to partsbins were located at various reach distances as determined usingavailable anthropometric data (Sengupta and Das, 2000). Reachesto 50% of the maximum reach were considered near distance rea-ches, reaches to 75% of maximum reach were considered middledistance reaches, and reaches to 100% of the maximum reach wereconsidered maximum reach distances. The angular locations of thebins with respect to the participant were identical left toright (Fig. 1). Using the sagittal plane as 0�, bins were located at�20�, �40�, and �60�. While any angular location could have beenchosen, those considered in this study were considered to berepresentative of common workstation setups. Anthropometricdimensions for the workstation setups are provided in Table 3. Allbin location distances were measured from the center of the tablealong the angle of interest.

Fig. 1. General worksta

2.2. Procedure

For the testing session, participants completed informed con-sent procedures approved by the Mississippi State University IRB,were fitted with data collection equipment, and were trained onthe first assembly. The experimental task included nine uniqueLEGO assemblies (three workstation configurations and three as-semblies per workstation configuration). All assemblies wereidentical and consisted of 24 pieces and were custom designed atapproximately the same level of difficulty. Participants stood withtheir feet shoulder width apart and their abdomen 2.54 cm awayfrom the workstation. To ensure participants were 2.54 cm awayfrom the workstation, a 2.54 cm � 15.24 cm board was attached tothe edge of the table. Afterward, the participants performed theassembly task under the supervision of the researcher. Initially,participants watched the researcher perform the assembly untilthey were ready to complete the assembly themselves. Participantswere allowed to practice on the assembly as long as they wished,and informed the researcher when they were ready to begin.

Participants completed three assemblies on the appropriateworkstation configuration and then moved to the next experi-mental condition. Once all the conditions for the small task as-sembles were complete, participants were asked to perform theMFFR experiments. Before performing the MFFR, the workstationwas cleared of the work bins and the participants were given anerasable marker for each hand. With their body touching the boardat the table’s edge, the participants reached forward maximallywithout bending and placed a mark on the work surface for each ofthe reach zones. When the MFFR data for each reach zone wascollected, data collection equipment was removed, any remainingquestions were answered, and the participant was compensatedmonetarily. Testing lasted approximately 2 h.

2.3. Equipment

Biometrics Data Log was used to capture the maximum jointangles of the neck, elbow, and torso. The Biometric Data Log is a

tion configuration.

Table 4Near reach ANOVA results.

Observed angles Factors

BMI Gender Workstation

Elbow extension ns ns ***Neck flexion ns ns ***Neck lateral B. ns * nsBack flexion ns ns ***Back lateral B. ns ns *

ns: not significant; * ¼ p < .05; ** ¼ p < .01; *** ¼ p < .0001.


portable data acquisition tool that allows researchers to collect bothanalog and digital goniometer data. The Data Log has Bluetoothtechnology, which allows real-time data to be transferred to aPCdwhich is automatically backed up with the memory card in thesystem. The software that was used is the Data Log PC softwareversion 6.01.

Four electrogoniometers were used to capture joint angle dataof interest for this research study. Two SG 110 s were used tocapture the flexion/extension of the left and right elbow. One SG110 was used to capture the flexion/extension and lateral flexion ofthe neck. One SG 150B was used to capture the flexion/extensionand lateral flexion of the torso. All datawere collected at 50 Hz withand excitation output of 200 mV.

Once all goniometers were attached according to manufacturerrecommendations, the researcher defined the zero angles for eachgoniometer individually while the participant stood erect. Zeroangles for the neck and torso were recorded as standing erect.Negative neck and back angles represent extension, and positiveangles represent flexion of the joints. Zero angles for the elbowwere set with the upper arm resting along the torso, elbows flexedat ninety degrees, and palms facing each other. Negative anglesrepresent elbow extension and positive angles represented elbowflexion.

Once the data were formatted correctly, a within groups boxplot was run with the dependent variables in the graph variablesslot and task number in the categorical variables slot. The outlierswere identified and removed from the data sets. The data wereseparated based on task, and then passed the test for equal vari-ances and the histogram for the residual plots appeared to followthe normal distribution. All the factors and their interactions wereincluded into the model. The ANOVA shows the results for themain factors only. Post-hoc analyses were performed on the databy using the Tukey method for comparisons of the main effectfactors.

Table 5Near reach zone joint angles (mean (S.D.)).

BMI groups

Reach angle Normal Overweight

Elbow extension 78.40 (16.40) 66.72 (12.74)Neck flexion 11.87 (12.34) 10.95 (5.11)Neck lateral B. 2.02 (1.40) 2.38 (1.62)Back flexion 6.69 (6.35) 4.01 (4.54)Back lateral B. 1.83 (1.51) 2.66 (1.50)

Gender

Reach angle Females Males


3. Results

3.1. Near reach zone

Results for observed angles for the near reach zone are shown inTable 4 and Table 5. For the main factors, the results for theobserved angles indicated the BMI did not affect any angle mea-sures. Gender was found to be significant for neck lateral bending,with females having significantly larger maximum neck flexionangels. Workstation configuration was found to be significant forelbow extension, neck flexion, back flexion, and back lateral flexion.Neck flexion was found to be significantly larger for the 5thpercentile configuration, while back flexion was significantlysmaller for the 5th percentile configuration when compared to the50th and 95th configurations. Other post-hoc comparisons yieldedno significant differences.

3.2. Mid reach zone

Results for observed angles for the mid reach zone are shown inTables 6 and 7. For the main factors, the results for the observedangles indicated BMI did not affect any of the observed anglemeasures. Gender was found to be significant for elbow extension,neck flexion, and neck lateral bending; and the workstation con-figurations were found to significantly affect all observed angles.Females’ elbow extension and neck lateral bending angles werefound to be significantly larger than the males, but males’ neckflexion angles were significantly larger than the females. In the midreach zone, Tukey pairwise comparison results indicated that neckflexion was significantly different at all three workstation config-urations, with the 5th percentile configuration demonstrating thelargest neck flexion, and the 95th percentile workstation demon-strating the smallest neck flexion. Back flexion was also signifi-cantly different for each of the three workstation configurations,with the 5th percentile workstation showing the smallest backflexion, and the 95th percentile configuration showing the largestback flexion.

3.3. Maximum reach zone

Results for observed angles for the maximum reach zone areshown in Tables 8 and 9. BMI was not found to affect any anglemeasures. Gender significantly affected for elbow extension, neckflexion, and neck lateral bending; workstation configurationsignificantly affected all observed angles. Female elbow extensionandneck lateral bending angleswere found to be significantly larger

Obese 1 Obese 2 Obese 3

76.02 (15.30) 76.99 (13.72) 80.33 (7.81)7.06 (7.01) 8.17 (10.80) 11.07 (8.55)2.41 (1.82) 2.46 (1.73) 2.89 (2.21)3.47 (6.28) 5.35 (5.44) 7.53 (5.11)2.10 (1.84) 2.21 (1.75) 1.84 (1.53)

Workstation

5th 50th 95th

72.89 (13.07) 75.50 (14.73) 78.44 (14.42)10.59 (8.43) 9.48 (9.13) 9.41 (9.80)2.40 (1.84) 2.41 (1.82) 2.52 (1.75)4.36 (5.33) 5.80 (5.76) 6.02 (6.11)2.03 (1.55) 2.15 (1.59) 2.23 (1.82)

Table 6Mid reach ANOVA results.



Elbow extension ns * ***Neck flexion ns ** ***Neck lateral B. ns * ***Back flexion ns ns ***Back lateral B. ns ns ***


Table 8Max reach ANOVA results.



Elbow extension ns ** ***Neck flexion ns ** ***Neck lateral B. ns * ***Back flexion ns ns ***Back lateral B. ns ns ***



than males, and the male neck flexion angles were found to besignificantly larger than females. Neck and back flexion was signif-icantly larger at the 50th and 95th percentile workstation configu-rations, compared to the 5th percentile workstation configuration.

3.4. Cross reach zone

Joint angle results for observed angles for the cross reach zoneare shown in Tables 10 and 11. Results indicated that BMI did notaffect any angle measures. Gender was found to be significant forelbow extension, neck flexion, and neck lateral bending; theworkstation configurations were found to significantly affect allobserved angles. Female elbow extension and neck lateral bendingangles were found to be significantly larger than males, thoughmale neck flexion angles were significantly larger than females. Allthree workstation configurations displayed were all significantlydifferent for both neck and back flexion with the largest valuesbeing observed at the 5th percentile configuration, and the smallestvalues at the 95th percentile configuration.

3.5. Maximum frontal functional reach results (MFFR)

ANOVA results for the MFFR are shown in Table 12. BMI groupwas found to significantly affect MFFR for all reach zones. Tukeyresults demonstrated that obese class 1 had a significantly greaterMFFR than obese class 2 group for the near, mid, and max reachzones. For the cross reach zone, the non-obese group had asignificantly greater MFFR than obese classes 2 and 3. Descriptivestatistics for MFFR mean reach by BMI groups and Gender areshown in Tables 13 and 14.

4. Discussion

The overall objective of this study was to quantify the effects ofBMI classification and workstation configuration on select body

Table 7Mid reach zone joint angles (mean (S.D.)).

BMI groups



Gender



joints. Results found that BMI had little effect on measuredmaximum joint angles, while which workstation configuration hadsignificant effects. The lack of significant findings for BMI classifi-cation is somewhat surprising as previous research has indicatedthat elbow angle variation (change in angle from the start of themovement to the end) was significantly larger for obese versusnon-obese participants (Berrigan et al., 2006). This discrepancymay be due to the fact that only the maximum angle observedduring the reach movement is reported here. This may be furthercompounded by the fact that Berrigan et al. (2006) found thatduring upper extremity targeting tasks, obese participants targetedobjects with their whole body (meaning that they linearly dis-placed their knee, hip, and shoulder to reach the target), while non-obese participants used mainly their shoulders. As this study didnot capture joint changes for the lower extremity or the shoulder, itis unknown if linear displacements in these joints could havemasked any elbow and torso joint changes.

As stated previously, workstation configuration was found tosignificantly affect measured joint angles, with joint anglesincreasing as the workstation configuration and reach distanceincreased. While the relative difference in these angles is small,previous studies have found an increase in pelvic tilt (comparableto what is observed in pregnant women (Larrson, 2004)) in theobese (Vismara et al., 2010). This increase in pelvic tilt can increaseflexion of the sacroiliac joints increasing the risk of degenerativedisc disorders (Vismara et al., 2010). Therefore, even small forwardflexion angles of the torso can result in even larger compressionand shear forces in the L5-S1 joint and discs (Sethi et al., 2011),thereby increasing the risk for chronic low back pain. Further,postural changes in the obese, particularly those changes associ-ated with the low back, can result in localized muscular fatigue, ashas been reported in previous studies (e.g., Descarreaux et al., 2008;Mayer et al., 2012). The increased localized muscle fatigue can in-crease postural instability (e.g., Petti et al., 1997; Owusu et al., 1998;Goulding et al., 2003; Berrigan et al., 2006; Nakipoglu et al., 2008),


99.18 (13.81) 101.98 (13.89) 102.05 (8.85)3.11 (7.21) 3.45 (10.97) 10.42 (7.74)3.84 (2.49) 4.48 (3.02) 4.23 (2.93)6.34 (6.56) 8.61 (6.49) 11.21 (6.19)2.85 (2.30) 2.41 (1.93) 2.75 (2.10)

Workstation

5th 50th 95th

96.17 (13.53) 100.46 (1303) 104.82 (12.93)8.21 (9.26) 7.20 (9.78) 4.81 (10.96)3.39 (2.44) 4.03 (2.66) 4.77 (2.91)5.87 (6.10) 8.01 (6.58) 9.82 (6.16)2.10 (1.72) 2.47 (1.96) 3.54 (2.46)

Table 9Max reach zone joint angles (mean (S.D.)).

BMI groups

Reach angle Normal Overweight Obese 1 Obese 2 Obese 3

Elbow extension 118.69 (11.13) 105.45 (14.13) 108.16 (10.45) 111.16 (10.33) 109.69 (10.53)Neck flexion �1.61 (16.98) �1.85 (9.43) �6.60 (9.00) �3.17 (13.64) 6.03 (7.24)Neck lateral B. 3.70 (3.76) 6.86 (4.00) 5.94 (4.18) 6.38 (4.38) 6.12 (3.85)Back flexion 14.45 (8.29) 9.43 (6.05) 12.13 (6.36) 13.78 (8.24) 18.63 (5.39)Back lateral B. 4.12 (2.78) 3.65 (2.76) 3.73 (2.47) 3.20 (2.86) 3.50 (2.76)

Gender Workstation

Reach angle Females Males 5th 50th 95th

Elbow extension 115.19 (12.07) 106.37 (10.93) 107.16 (11.85) 111.90 (11.90) 113.21 (12.37)Neck flexion �7.62 (12.06) 3.93 (10.07) 2.44 (11.29) �2.09 (11.65) �5.81 (13.20)Neck lateral B. 6.94 (4.54) 4.74 (3.51) 4.69 (3.43) 5.76 (4.16) 7.12 (4.62)Back flexion 14.20 (8.17) 12.95 (6.93) 10.42 (6.79) 13.90 (7.30) 16.85 (7.26)Back lateral B. 3.54 (2.65) 3.75 (2.81) 2.84 (2.29) 3.40 (2.63) 4.89 (2.91)

Table 10Cross reach ANOVA results.



Elbow extension ns * ***Neck flexion ns ** ***Neck lateral B. ns * ***Back flexion ns ns ***Back lateral B. ns ns **



and possibly increase musculoskeletal injury risk, particularly lowback injury. These results add to the body of work concerning howworkstation configuration can positively influence overall workerwellbeing (Cimino et al., 2009; Fogliatto and Guimarase, 2004;Nanthavanij, 1996).

Maximum forward functional reach (MFFR) was found to besignificantly shorter for obese class 2 and 3 participants, similar toSingh et al. (2009). In that study, the authors concluded that currentreachable workspace data and models for ergonomic workstationdesignmay not be applicable for the obese population because datawere gathered from mostly non-obese individuals. In general, thework envelope of obese individuals is much smaller due to an in-crease in abdominal depth. Current workstation standards mayresult in an increase in extended reaches which are known to in-crease shoulder musculoskeletal complaints (NIOSH, 1997), andpossible twisting of the torso to reach the outer perimeter of the

Table 11Cross reach zone joint angles (mean (S.D.)).

BMI groups



Gender


Elbow extension 105.72 (14.19) 98.18 (11.96)Neck flexion �1.60 (9.81) 7.92 (9.83)Neck lateral B. 4.18 (2.72) 2.96 (2.58)Back flexion 9.73 (7.00) 9.38 (6.60)Back lateral B. 2.59 (2.01) 2.77 (2.18)

work envelop (as evidenced by our resultsdincreased torso lateralbending) which are known to increase risk of low backdisorders (NIOSH, 1997), among others. Berrigan et al. (2006) alsofound that movement time for upper arm movements wasincreased for obese individuals, and that this finding was furtherimpacted by increases in the index of difficulty of the task (i.e., theprecision on the task). This can lead to the need to work extendedhours due to decreased productivity or increased time spent innon-neutral postures which can increase musculoskeletal injuryrisk. However, further research is needed to truly understand howworker behaviors in terms of kinetics and kinematics are impactedbased on obesity.

With respect to gender, the results supported previous work byO’Sullivan and Gallwey (2002). For all four reach zones (near, mid,cross, and max), results demonstrated that female participants hada larger elbow extension than male participants. The differenceswere significant in all but the near reach zone. These findings mayprovide support for studies indicating that females are at risk forupper extremity disorders (NIOSH, 1997).

There were several limitations in this study. First, obesity in thisstudy was defined based on standard BMI categories. While this isone of the simplest and most commonly used measures of obesity,it has known inaccuracies (e.g., Burkhauser and Cawley, 2008;Romero-Corral et al., 2008). Other measures of obesity may pro-vide additional insights into differences in postures assumed dur-ing dynamic upper extremity assembly tasks between obese andnon-obese individuals. Second, only maximum joint anglesobserved for the elbow, neck and shoulder were reported. Inclusion


101.17 (12.73) 102.15 (12.27) 102.16 (11.27)�1.36 (7.75) -0.67 (12.17) 8.00 (7.21)3.57 (2.77) 4.35 (2.92) 4.07 (2.76)8.30 (6.64) 10.26 (7.51) 14.24 (5.41)2.56 (2.14) 2.31 (1.79) 2.33 (1.95)

Workstation

5th 50th 95th

97.81 (13.36) 102.66 (13.44) 106.08 (12.82)5.68 (10.12) 3.01 (10.42) 0.32 (11.65)3.13 (2.36) 3.56 (2.81) 4.11 (3.02)7.47 (6.17) 9.91 (7.12) 11.65 (6.45)2.56 (1.98) 2.63 (2.06) 2.90 (2.26)

Table 12Maximum frontal functional reach ANOVA results.

ns: not significant; * ¼ p < .05; ** ¼ p < .01; *** ¼ p < .0001

Reach zones Factors

BMI Gender BMI*Gender

Near Reach * ns nsMid Reach * ns nsCross Reach ** ns nsMax Reach ** ns ns

Table 14Maximum frontal function mean reach by gender (mean (S.D.)).

Gender

Reach zone Females Males

Near 33.18 (2.86) 35.10 (4.15)Mid 33.53 (3.28) 34.82 (4.17)Cross 30.50 (3.62) 31.60 (4.66)Max 31.60 (3.21) 32.79 (3.78)


of other body joints is warranted given the growing volume ofliterature on body displacement of obese participants when per-forming upper extremity tasks. Third, while the sample size isgenerically considered sufficient for statistical analyses, the rangeof BMI classifications may warrant an increase in participantnumbers.

5. Conclusion

When designing a workstation in industry, production man-agers should re-evaluate the layout of their workstations. Twoemployees of the same gender and similar height may have con-flicting levels of comfort while working at a workstation. The re-sults indicated work bins located farther away from the assemblycenter have a greater impact on the body than work bins locatednear the assembly center. Ensuring the work is located within themaximum reach envelope of the 50th percentile workstationconfiguration would reduce the chances of back and neck injurieswhich are the most affected by the design of the workstation.

Production managers should be aware how workstation layoutaffects females and males differently. Females’ reach angles at anindividual workstation setup tend to be significantly higher thanmales’ reach angle for the elbow and back in the far reach zones.Onceworkstation designs have been approved and implemented inthe workforce, the managers should ensure female workers areable to complete all work functions comfortably at the workstationwithout functional limitations. According to the MFFR, heavieremployeesdin comparison to their normal weight counter-partsdprefer their work bins are nearer in reach. Not only shouldthe work bins be nearer for the larger individuals, but they shouldbe elevated to reduce pressure on joint angles while working.

There is a need for further studies of the differences betweengender differences between the obese groups while performingwork tasks. Future work should be performed to study the effects ofjoint angle on Body Volume Index (BVI). Since BMI is based only onthe height and weight individuals, it does not consider the bodyshape or body composition of an individual, which is critical whentrying to understand differences in functional limitation. BVI givesan indication of the anatomical location where fat is stored onobese individuals. The study design should use BMI for classifica-tion purposes but use BVI to select the participants whose fatlocation is in the abdominal area. Studying the functional limitation

Table 13Maximum frontal function mean reach by BMI groups (mean (S.D.)).

BMI groups

Reachzone

Normal Overweight Obese 1 Obese 2 Obese 3

Near 35.51 (2.65) 34.82 (1.35) 36.5 (3.83) 30.53 (3.02) 33.27 (3.90)Mid 35.98 (3.15) 35.57 (1.61) 36.13 (3.83) 30.28 (2.74) 32.90 (3.70)Cross 33.91 (3.27) 33.56 (1.87) 32.63 (4.12) 27.31 (2.71) 27.85 (3.19)Max 34.62 (1.79) 34.56 (1.61) 32.56 (4.06) 29.08 (2.59) 30.14 (3.15)

of the obese in conjunction with the use of BVI would be anessential next step in understanding the effects that body size andshape have on joint movement.

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Effects of BMI and task parameters on joint angles during simulated small parts assembly