Transformational mechanism(s) of neuromuscular activation and performance in human development

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Many factors affect muscular force and power. The proposed research program focuses on neurophysiological factors with the overall goal of establishing a comprehensive understanding of muscle functional control mechanisms and factors affecting them. We will examine peripheral, central and hormonal factors using a unique approach highlighted by the child-adult transition model, whereby known physiologic and functional muscular changes are associated with known muscle activation changes. Human maturation, particularly the pubertal period, involves wide-ranging changes. Size-normalized muscle force, speed, and power increase dramatically, while the nature of motor-unit (MU) utilization and muscle composition, also appear to change. Understanding the factors determining MU activation is central to understanding muscle functional control and neuromotor development and will be examined through the child-adult transition model. During the next 5 years, we will study peripheral and central indicators of MU activation and their inter-relationship during maturation. These indicators will be examined via traditional surface electromyography (EMG) as well as by the recently-developed technology allowing for the spatial and temporal decomposition of multiple simultaneous EMG signals. This non-invasive technique, ethically suitable for children, allows for identification of individual MUs during muscle contraction and thus, allows for characterization of distinct MU groups and activation patterns. We will explore those patterns, along with known peripheral indicators of MU activation, such as activation deficit and high-threshold MU recruitment onset, in children and adults of both sexes. Changes in the inter-relationship of these indicators, during the child-adult transition period, will shed light on the relative contribution of peripheral vs. central factors affecting muscle function. Since hormonal changes characterize the child-adult transition period and have been shown responsible for numerous maturational- and sex-related functional changes, hormonal effects (mainly, sex hormones) will also be investigated as possible determinants of muscle activation and its control. Finally, the potential of external interventions, such as specific forms of physical training, to affect muscle activation capacity (e.g., activation deficit, onset of higher-threshold MU recruitment) will be investigated to shed light on the involved control mechanisms. This work is important for understanding the fundamental mechanisms underlying changes in muscle functional and metabolic characteristics, and will provide novel insights into the fundamental nature of neuromotor development. Since most pediatric conditioning and rehabilitation programs are based on adult-originated data, our work will also inform age-appropriate strategies to enhance neuromuscular function.