Date of Award
Master of Science (MS)
Purpose: The purpose of this study was to investigate the effect of two similar low force, upper arm holding tasks on shoulder muscle fatigue. One task involves static holding, while the comparison task involves limited up and down motions, dynamic rolling. Both tasks require the shoulder muscles to hold the combined weight of the arm, hand, and a roller brush in a manner similar to that of a painter standing on a portable ladder painting a wall.
Methods: Twenty volunteer participants from undergraduate classes performed two similar tasks. One was holding their dominant arm above their shoulder while holding a roller paint brush against a target (static holding). The other tasks was similar except the participant moved the roller brush up and down on a defined target (dynamic rolling). During each task, participants wore surface electromyography sensors placed on anterior, medial, and posterior deltoids, and on the triceps muscle of their dominant arm in the direction of the muscle fibers. For each participant, the maximum voluntary contraction of each muscle was assessed and normalized to their muscle activity for a static holding and dynamic rolling task. Muscle fatigue was assessed throughout the task by performing a median frequency analysis on the muscle activity data. Discomfort ratings were measured verbally over the task period on a 0–100 scale. The task was performed up to a rating of 80, indication of extreme discomfort.
Results: Analyses based on of median frequency recordings showed no significant difference in the rate of fatigue development between all four muscles. Rate of fatigue was also not significantly different between static holding and dynamic rolling tasks. Static holding and dynamic rolling endurance times were significantly different from one another (p = 0.0066). Analyses based on discomfort ratings showed static holding had a maximum endurance time of 9.5 minutes and dynamic rolling had a maximum endurance time of 6.5 minutes. Endurance times were also compared to 20 minutes—a time mentioned in the notes of the Upper Limb Localized Fatigue Guidelines of the American Conference of Governmental Industrial Hygienist saying static exertions of the upper limbs “would not be expected to exceed 20 minutes.” There was a significant difference in static holding and dynamic rolling endurance times against a 20-minute note (p = 0.000).
Conclusion: The results demonstrated that shoulder muscle fatigue and discomfort were present during the tasks. The endurance times differed between static holding and dynamic rolling tasks. The endurance times never exceeded 20-minutes, thereby supporting the comment within the Upper Limb Localized Fatigue Guidelines.
Ericson, Kayla, "STATIC SHOULDER ELEVATION WITH OR WITHOUT LIMITED RANGE OF ARM MOTION" (2019). Graduate Theses & Non-Theses. 209.