The effect of maximum voluntary contraction on endurance times for the shoulder girdle.
Garg A; Hegmann KT; Schwoerer BJ; Kapellusch JM
Int J Ind Ergon 2002 Aug; 30(2):103-113
This study investigated endurance times as percentages of maximum voluntary contractions (MVCs) in 12 healthy females (mean 25.874.3 years) in 5 postures and at 7% MVCs. The shoulder postures utilized were 30/90 (shoulder forward flexion=301 and included elbow angle=901), 60/90, 90/120, 120/150, and 150/180.The %MVCs were 5%, 15%, 30%, 45%, 60%, 75%, and 90% of MVC at each of these postures.Outcome measures included: endurance times, ratings of perceived exertion, fatigue ratings, pain ratings, and surface electromyography (trapezius and middeltoid). As expected the endurance time decreased non-linearly with an increase in %MVC.However, the relationship between endurance time and %MVC differed significantly from Rohmert's curve and suggests it considerably overestimates endurance times for %MVCs o45% and it underestimates endurance times for %MVCs >45%.This study's curve did not become asymptotic even at 5% MVC.Shoulder posture (shoulder forward flexion angle) had a significant effect on endurance time.In general, endurance time decreased with an increase in shoulder flexion angle up to 1201 and then it increased.Thus, overhead work (hands above the head) would appear to be better designed with a greater degree of forward flexion, rather than in front of the worker at lower degrees of forward flexion.
Ergonomics; Musculoskeletal-system; Women; Muscle-contraction; Muscle-stress; Posture; Endurance-tests; Fatigue; Pain-tolerance; Physical-capacity;
Author Keywords: Endurance; Shoulder; Shoulder girdle; Rohmert's curve; Ergonomics; Electromyography
A.Garg, Department of Industrial and Manufacturing Engineering, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA
International Journal of Industrial Ergonomics
University of Utah, Salt Lake City, Utah