Wrist position affects muscle fatigue during isometric contractions of wrist flexors: An exploratory study

Abstract

ObjectiveTo investigate the influence of wrist position and torque level on lower arm flexor muscle fatigue. BackgroundWork-related musculoskeletal health risks at the wrist joint may depend on joint position and torque level, as proposed by ergonomic workplace assessment tools. As empirical data are scarce, muscle fatigue, as proxy of work-related musculoskeletal health risks, can be used to explore this assumption. Method18 healthy participants performed fatiguing isometric wrist flexion contractions in three wrist positions (40° flexion, 0° neutral position, and 40° extension) and torque levels (10, 20, 40% of the maximum voluntary contraction). Electromyographic signs of fatigue were analyzed in the flexor carpi radialis (FCR) and flexor digitorum superficialis (FDS) muscles. ResultsMuscle fatigue was dependent on torque level and wrist position and differed between muscles. Signs of fatigue were more evident at higher torque levels for both muscles. While fatigue signs in FCR were not clearly associated with wrist position, the FDS fatigued more during wrist flexion. An interaction effect between torque level and wrist position was not observed. ConclusionHigher torque levels induce greater signs of local muscle fatigue in wrist flexor muscles, and a 40° wrist flexion triggers fatigue, while 40° wrist extension does not. Our data do not support the assumption of increased risk in greater wrist angles in any direction by prevailing ergonomic risk assessments. Relevance to industryPeople with work-related wrist flexor effort may be at increased risk of musculoskeletal disorders when higher torques are applied and flexed wrist positions are required.