The effects of muscle fibre type distribution on gait biomechanics: A predictive simulation study

Muscle fibre type distribution influences both metabolic and contractile properties of muscles and its influence on gait biomechanics is difficult to investigate \textit{in vivo}. This study aimed to predict the influence of muscle fibre type distribution on the metabolic cost and biomechanics of simulated gait. A muscle model that independently represented slow and fast twitch fibres was implemented in a predictive musculoskeletal simulation framework and used to investigate how cost of transport, stride length, stride frequency, and mechanical work performed by slow and fast twitch fibres were influenced by fibre type distribution across locomotion speeds (1.0 - 4.5 m {middle dot} s-1). Cost of transport decreased as proportion of slow twitch fibres increased, while stride length and frequency were minimally affected by fibre type distribution during walking. During running, cost of transport decreased and increased with increasing proportions of slow twitch fibres above and below a threshold speed, respectively. Stride frequency decreased and stride length increased with increasing proportions of slow twitch fibres above this speed. These shifts in spatiotemporal characteristics may allow key muscles to operate close to their peak mechanical efficiency. In conclusion, fibre type distribution may influence both the energetics and biomechanics of gait in a locomotion speed dependent manner.