Shoulder muscle fatigue development in young and older female adults during a repetitive manual task

Abstract

Age may modify the association between occupational physical demand and muscle loading, and ultimately increase the risk of musculoskeletal disorders. The goal of this study was to investigate age-related differences in shoulder muscle fatigue development during a repetitive manual task. Twenty participants in two age groups completed an 80-minute simulated low-intensity assembly task. Electromyographic (EMG) manifestation of muscle fatigue was observed in the upper trapezius, deltoid and infraspinatus muscles in both age groups, and coincided with an increase in the subjective ratings of perceived exertions. Compared with the younger group, older group showed a more monotonic decrease in EMG power frequency in the upper trapezius and deltoid muscles. However, the age-related difference in EMG amplitude was less consistent. Relative rest time of the upper trapezius muscle in the older group was less than the young group throughout the task. The observed patterns of EMG measures suggest that older participants may have disadvantages in fatigue resistance in the upper trapezius and posterior deltoid muscles during the simulated repetitive manual task.

Abstract

Practitioner Summary: A rapidly ageing workforce in the USA and other countries poses new challenges for preventing work-related injuries. This study showed that during an 80-minute repetitive light manual work, older adults exhibited more consistent patterns of electromyographic manifestation of shoulder muscle fatigue and less rest in the upper trapezius muscle than young adults.

Keywords::

• age
• shoulder
• muscle fatigue
• electromyography
• repetitive work

Acknowledgements

The authors thank Dr Nils Fallentin and Dr Yulan Liang for their comments and suggestions to improve this manuscript, and Jacob Banks, Niall O'Brien and Amanda Rivard for their assistance in data collection.