Age-related differences in muscular force application: differentiating between the influences of growth and maturation of the neuro-motor system

As children grow older, multiple factors result in changes in motor behavior. These changes can be revealed in differences in the application of muscular forces, which give us information about the nervous system’s contribution to the task. To allow for a valid interpretation of age-related differences in muscular force application, two general methodological assumptions must be made. The method to estimate muscular forces must be suitable, and age-related differences in muscular force application must not be confounded by factors other than those to which observed differences are attributed. The goal of this dissertation was to distinguish between the contributions of growth and maturation to age-related differences in muscular force application. Distinguishing between these two factors is important because the interpretation of observed differences in muscular force application might be different, depending on their source. Three studies were performed. The first study was an investigation of the effect of growth on muscular force application using two different methods that have been viii previously used to answer developmental questions. The results of this study revealed that the answer to the question of how growth affects the application of muscular forces depends on the biomechanical technique used. Based on these results, an analysis of intersegmental dynamics was chosen as the method for Studies 2 and 3. Studies 2 and 3 were designed to differentiate between the influences of growth and maturation of the neuro-motor system on children’s adaptability in terms of muscular power production. Results of Study 2 revealed that during pedaling, segmental growth has a significant effect on how muscular power is transferred through the limbs to the crank. Results of Study 3 showed that if children perform a cyclical dynamic task at a high movement speed, a reduction in muscular power production results in a weaker synergy of intermuscular coordination. The results of this dissertation increase our understanding about the factors that lead to age-related improvements in adaptation and let us speculate about the factors that are limiting children’s performance ranges. They have practical implications for teachers and coaches and are important prerequisites for future research.