Effects of age on muscle activity and upper body kinematics during a repetitive forearm supination task

Abstract

The principal objective of this study was to assess the effects of age on upper extremity muscle activation patterns and upper body kinematics during a forearm supination task. Age-related physiological and biomechanical changes in the musculoskeletal system have been documented in the literature. It was hypothesized that these changes may have an impact on muscle recruitment and work technique (postural/kinematic) employed during work tasks. A simple repetitive forearm supination task was used to evaluate these hypotheses. Twenty subjects (ten in each age group 19–29 and 55–65) performed a series of static and dynamic forearm supination tasks on a work simulator. These exertions were performed at eight different levels of supination torque: 5–40 lb-in in 5 lb-in increments. As the subjects performed the static exertions the activation levels of several key muscles of the upper extremity were captured using surface electromyography. As the subjects performed the dynamic exertions, the motions of the upper body and upper extremity were captured using a magnetic field-based motion analysis system. The results of the static exertions showed that older subjects generated 135% greater trapezius muscle activity (significant at p < 0.05 level) but no other muscle group sampled showed a significant difference between the age groups. In the dynamic exertions, age had no effect on upper limb/torso kinematic responses. In both the static and dynamic exertions, supination torque level had a significant impact on muscle activity and kinematics. These results provide empirical evidence that age alone does not have a consistent impact on biomechanical responses during physically demanding work tasks.