Estimation of the effects of hand growth on muscle activation patterns: A musculoskeletal modeling study.

Abstract

Throughout childhood growth and development, both the nervous and the musculoskeletal systems undergo rapid change. The goal of this study was to examine the impact of growth-related changes in skeletal size and muscle strength on the neural control of finger force generation. By modifying an existing OpenSim hand model in accordance with pediatric anthropometric data, we created 10 distinct models representing males and females at each year of development from 6 to 10 years old. We then used the static optimization tool to estimate the requisite muscle activations to create a maximal palmar force with the index finger in two different postures (metacarpophalangeal, proximal interphalangeal, distal interphalangeal) - Posture 1: (0°, 30°, 0°) and Posture 2: (0°, 60°, 30°). For Posture 1, multiple regression analysis revealed a significant effect of both age and sex on activation for all muscles (p < 0.035) with exception of the flexor digitorum profundus. For Posture 2, only the extensor digitorum communis activation had a significant relationship with age (p = 0.010), while no other muscles showed a significant relationship with age, sex, or the age-sex interaction activation (p > 0.054). Exchanging the activation patterns between the youngest and oldest models altered both the predicted index finger force and direction. Therefore, our simulations suggest that the changes in hand size and morphology associated with growth may necessitate changes in muscle activation patterns to be able to continue to perform a given hand function. Children may need to substantially adjust or even relearn motor control strategies throughout childhood.