Dan Anton

The effect of overhead drilling position on shoulder moment and electromyography

The effect of overhead drilling tasks on electromyographic (EMG) activity and shoulder joint moment was examined in this study. Twenty subjects simulated an overhead drilling task using a close, middle and far reach position while standing on either a lower or a higher step of a stepladder. Root mean square amplitude (AMP) of EMG activity from the dominant side anterior deltoid, biceps brachii and triceps brachii muscles was used to determine muscular load. Digital video was used to determine shoulder joint moment using 2-dimensional static link segment modelling in the sagittal plane. The results demonstrated that, compared to the far reach position, using the close reach position significantly decreased anterior deltoid AMP and biceps brachii AMP and moment, but increased triceps brachii AMP. Compared to the lower step, using the higher step significantly decreased anterior deltoid AMP and triceps AMP and moment, while increasing biceps AMP in the close position. There was no significant change noted in EMG median frequency indicating that fatigue was minimized. Moment increased monotonically with AMP. The findings indicated that workers performing overhead tasks should work close to their body in order to minimize shoulder forces. The implications of this recommendation are discussed.

Test-Retest Reliability of a Self-Administered Musculoskeletal Symptoms and Job Factors Questionnaire Used in Ergonomics Research

The purpose of this study was to investigate the test-retest reliability of questionnaire items related to musculoskeletal symptoms and the reliability of specific job factors. The type of questionnaire items described in the present study have been used by several investigators to assess symptoms of musculoskeletal disorders and problematic job factors among workers from a variety of occupations. Employees at a plastics molding facility were asked to complete an initial symptom and jobs factors questionnaire and then complete an identical questionnaire either two or four weeks later. Of the 216 employees participating in the initial round, 99 (45.8%) agreed to participate in the retest portion of the study. The kappa coefficient was used to determine repeatability for categorical outcomes. The majority of the kappa coefficients for the 58 questionnaire items were above 0.50 but ranged between 0.13 and 1.00. The section of the questionnaire having the highest kappa coefficients was the section related to hand symptoms. Interval lengths of two and four weeks between the initial test and retest were found to be equally sufficient in terms of reliability. The results indicated that the symptom and job factors questionnaire is reliable for use in epidemiologic studies. Like all measurement instruments, the reliability of musculoskeletal questionnaires must be established before drawing conclusions from studies that employ the instrument.

Effect of Aviation Snip Design and Task Height on Upper Extremity Muscular Activity and Wrist Posture

Hand tools described as ergonomic in design are intended to reduce exposure to physical risk factors associated with work-related musculoskeletal disorders. Additionally, using the right tool for the job is believed to reduce exposure and, consequently, risk of disease. Sheet metal workers frequently use a cutting tool called aviation snips when fabricating and installing ductwork. The purpose of this laboratory simulation study was to determine the effect of (1) aviation snip design; and (2) work height on muscle activity, wrist posture, and user satisfaction among sheet metal workers. We hypothesized that specific aviation snips designs would be most appropriate for use at specific heights. Twenty-three sheet metal workers used three different designs of aviation snips to make curved cuts in sheet metal placed both at waist height and shoulder height. Conventional circular snips, straight snips, and an alternate design of offset snips were used. Upper extremity muscle activity was measured with surface electromyography, wrist posture was measured with electrogoniometry, and user satisfaction was rated by the participants on a survey. Statistically significant effects of snip design and task height on muscle activity, wrist posture, and user satisfaction were observed. However, no snip was preferable for all dependent variables. Work height had a greater effect on muscle activity and wrist posture than snip design. Field studies are indicated to determine the long-term effect of snip design on physical risk factors and risk of musculoskeletal disorders.