Applied Research: Upper Extremity Work

Shoulder Muscle Fatigue During Repetitive Tasks as Measured by Electromyography and NearInfrared Spectroscopy

Summary:   This study quantified shoulder muscle fatigue during repetitive exertions similar to motions found in automobile assembly tasks.   There was found to be significant shoulder muscle fatigue as a function of shoulder angle, task frequency, and force level.  Ergonomists should examine interactions of force and repetition as well as shoulder angle and repetition when evaluating the risk of shoulder MSDs.  For activities requiring work at ten repetitions per minute, the impact of force level was found to be much greater than at reduced levels of repetition.

Grip Force And Muscle Activity Differences Due To Glove Type

Summary:  Although the benefits of gloves to hand safety are well known, less information exists regarding the effects gloves may have on the quality and efficiency of work performed, or the potential risk due to cumulative trauma.  This study investigated the effects of different types and sizes of gloves on external grip force and muscle activity.  It was found that:

• Generally, gloves reduced peak grip strength.

• Different glove types have different effects on peak grip strength. Thinner, more elastic materials such as jersey and surgical gloves allowed for the greatest external force output.

• Barehanded exertions, and exertions performed wearing surgical and oversized surgical gloves, provided greater transfer of flexor muscle activity to grip force than many of the other glove types.

• Better-fitting gloves resulted in better transmission of muscular force to measured grip force.

• Significant differences exist between the ratios of force to coactivity between different glove types.

Industrial Wrist Motions And Incidence Of Hand/Wrist Cumulative Trauma Disorders

Summary:  A void in the study of occupational hand/wrist cumulative trauma disorders (CTDs) is the lack of quantification of the relationship between known kinematic workplace risk factors, such as wrist angle and repetition, and CTD risk.  A metric was formed from industrial workers’ wrist motions gathered during production tasks. Motions gathered included position, velocity, and acceleration of hand/wrist in the radial/ulnar, flexion/extension, and pronation/supination planes of motion.  Multivariate analyses found that acceleration in the flexion/extension plane discriminated the best between groups of low and high incidence rates of CTDs.  This metric can serve as preliminary motion benchmark to establish relative risk levels of CTDs for hand-intensive, highly repetitive jobs that do not require hand tools. Industrial practitioners can use this methodology, along with other accepted tools, to enhance ergonomic assessments of jobs.