Human motor control during movements with high demands

Introduction & Purpose During training and competition, athletes must cope with numerous demands that can influence their performance. These include physiological and mental fatigue, psychological stress, and the ability to adapt quickly to varying situations. Controlling the high number of degrees of freedom with which the musculoskeletal system can produce movements is challenging for the central nervous system CNS (Bernstein, 1967), even without the context of a sporting setting. One common theory in the field of motor control posits the existence of muscle synergies (Turpin et al., 2021). These are constituted of synergy vectors within the spinal cord that comprise the relative weightings of different co-active muscles. Synergy vectors are activated by time-varying activation coefficients, which correspond to the central commands from supraspinal areas. Consequently, the CNS is not required to individually time and scale the activation of each muscle independently; rather, it only regulates the activation of a limited number of synergies (Turpin et al., 2021). This simplification strategy has been extensively studied in a variety of settings, including locomotion (Boccia et al., 2018; McGowan et al., 2010) and reaching movements (Scano et al., 2019). However, muscle synergies were rarely studied in sport-like settings which demands fall beyond daily tasks. In this light, we conducted several studies in order to build a deeper understanding of motor control in movements with high demands. This abstract presents a summary of the main findings of four studies. Specifically, SKATE, examining the complex movements of skateboard tricks; LEARN, demonstrating modifications as participants learned to walk on a tightrope; STRESS, investigating alterations under psychological stress during treadmill walking; and FATIGUE, exploring the fatigue strategies of climbers during overhead hanging tasks. The overarching aim of these studies was to enhance our understanding of motor control and adaptation in movements of a high-demand nature. Methods To study muscle synergies, surface electromyography signals from multiple muscles were recorded, filtered, rectified, amplitude- and time-normalised, and concatenated across captured trials. Subsequently, factorisation algorithms were employed to extract the spatial synergy vectors and time-varying activation coefficients for each participant. The required number of synergies to perform the movement was then determined by the