Meeting Abstract
Muscles generate force and energy required to produce and control movement. Three factors critical to a muscle’s role are the mechanical demands of the movement (e.g. walking vs. running), location (e.g. proximal vs. distal) and muscle-tendon unit (MTU) design (e.g. short fibred vs. long fibred and presence of a tendon). These factors determine if a muscle favours a primary functional role such as storing elastic strain energy like a spring and generating force economically. During maximal sprint acceleration, the mechanical demands on the lower limb muscles transition from generating maximal positive work output during the start of the acceleration phase to maintaining net work output during the maximal steady sprint phase. Acceleration, therefore, allows us to characterise the functional role of muscles as mechanical demand changes within a specific motor task. We used a muscle-specific index-based approach in conjunction with computational simulations to characterise the role of the muscle-tendon unit (MTU) and muscle fibre in a subset of human lower limb muscles into four indices: strut-, spring-, motor-, and damper-like functions. Our index-based approach identified that both the MTU and muscle fibres in human lower limb muscles, which generated substantial mechanical work, exhibited greater motor-like function during the start of the maximal acceleration compared with the end. Further, despite possessing MTU designs favouring force economy, the MTUs of more distal muscles (i.e. ankle plantarflexors) also exhibited a significant shift from a motor-like function to a purely spring-like function as a steady speed was reached. We conclude that, although MTU architecture influences mechanical function, a muscle’s functional role can vary substantially when mechanical demands, such as acceleration, must be met. (NIH AR055648).
