Velocity-Dependent Neural Strategies of Explosive Force Production: Insights from Motor Unit Behaviour and Velocity-Based Training By Jesse Collins PhD Candidate Wilfrid Laurier University DISSERTATION Submitted to the Department/Faculty of Kinesiology in partial fulfillment of requirements for the degree of Doctor of Philosophy © Jesse Collins 2025 Abstract The overarching purpose of this dissertation was to identify the neuromuscular mechanisms that contribute to explosive strength gains following velocity-based training (VBT). VBT prescribes training loads and intensities based on the speed of movement during an exercise, using real-time velocity feedback to adjust effort and optimize training outcomes. This approach aims to develop high-velocity force production, which may be particularly effective for enhancing explosive athletic tasks (e.g., sprinting and jumping) that are too brief in duration to reach peak torque. This work provides insight on how the nervous system controls force development across a wide range of contraction velocities and assesses how VBT might modify neural strategies, specifically, motor unit firing rates of the prime movers and patterns of antagonist and synergist muscle activation. This dissertation includes three studies which each address a key objective. The first objective (Study 1) was to investigate how motor unit (MU) firing behaviour is modulated during dynamic isokinetic contractions across a wide range of movement velocities, to better understand the neural control of rapid force production. A secondary aim of this study was to assess the feasibility of using multi-electrode surface array electromyography decomposition to measure MU behaviour during high-velocity dynamic tasks. This study demonstrated that while decomposition is feasible during dynamic movement, limitations in detecting high-frequency discharges, specifically during the early-phase of the contraction (first 50ms), highlights the need for more sensitive methods to fully characterize neural drive during explosive tasks. The second objective (Study 2) was to assess how MU firing behaviour adapts to produce different contraction velocities during isotonic movements. Our results revealed that the muscle activation strategy changed over the course of the contraction. Specifically, during the early phase (first 50 ms), motor unit firing rates and the speed at which units were recruited varied based on the intended movement velocity. In contrast, during the later phase of the contraction, firing rates increased primarily in proportion to the torque being produced. Additionally, velocity-dependent modulation of antagonist and synergist muscle activation was observed during jumps at different velocities which suggests that coordinated adjustments in intermuscular control may be used to match specific task demands. The third objective (Study 3) was to assess whether velocity-specific neural strategies, such as motor unit firing characteristics and patterns of antagonist and synergist muscle activation, are trainable. Twenty-one resistance-trained athletes completed a four-week VBT intervention. which resulted in improvements in early-phase rate of force development (RFD) and synergist muscle activation Although we did not observe group-level changes in MU discharge rates, individual performance gains were correlated with increases in initial rate of force development and increased motor unit firing rates following training. This highlights inter-individual variability in adaptations to VBT. All together these studies show how VBT influences neuromuscular control of force during dynamic movement with evidence that both muscular adaptations (e.g., increased rate of twitch force development) and neural mechanisms (e.g., increases in motor unit firing rates associated with performance gains) contribute to these effects. This provides mechanistic insight into how the nervous system and musculature may adapt to velocity-specific training interventions. These results may also have practical implications for designing individualized training and rehabilitation programs that optimize rapid force production by targeting both neural timing and mechanical output under specific velocity constraints.
Jesse Collins (Thu,) studied this question.