Muscle fiber type effects on energetically optimal cadences in cycling

Fast-twitch (FT) and slow-twitch (ST) muscle fibers vary in their mechanical and energetic properties, and it has been suggested that muscle fiber type distribution influences energy expenditure and the energetically optimal cadence during pedaling. However, it is challenging to experimentally isolate the effects of muscle fiber type on pedaling energetics. In the present study, a modeling and computer simulation approach was used to test the dependence of muscle energy expenditure on pedaling rate during submaximal cycling. Simulations were generated using a musculoskeletal model at cadences from 40 to 120 rev min(-1), and the dynamic and energetic properties of the model muscles were scaled to represent a range of muscle fiber types. Energy expenditure and the energetically optimal cadence were found to be higher in a model with more FT fibers than a model with more ST fibers, consistent with predictions from the experimental literature. At the muscle level, mechanical efficiency was lower in the model with a greater proportion of FT fibers, but peaked at a higher cadence than in the ST model. Regardless of fiber type distribution, mechanical efficiency was low at 40 rev min(-1), increased to a broad plateau between 60 and 100 rev min(-1) , and decreased substantially at 120 rev min(-1). In conclusion, muscle fiber type distribution was confirmed as an important determinant of the energetics of pedaling.