Meeting Abstract

P1.152  Monday, Jan. 4  Muscle pennation and bulge varies with the mechanical demands of a movement WONG, I.*; WAKELING, J.M.; Simon Fraser University iww2@sfu.ca

During locomotion we can move at a wide range of speeds. Yet such movements are powered by muscle fibres that are most effective at a more limited range of speeds. It would make mechanical sense for the architectural gearing ratio (AGR: ratio of muscle velocity to fibre velocity) to alter to ensure that the fibres contribute effectively over a broad range of movement speeds. Geometric arguments predict that for a given muscle volume and fibre length, the pennation angle covaries with the muscle bulge. As a consequence the AGR is influenced by both the pennation angle and bulge on the muscle. Recently it has been suggested that rotations of the muscle fibres contribute to altered gearing (this was demonstrated in an isolated muscle preparation where the force and velocity of the contraction were coupled). Here we use ultrasound data from the triceps surae muscles during cycling at a range of loads and cadences to investigate the contribution of pennation angle and muscle bulge to AGR in vivo. Fibre rotations appeared more sensitive to load than cadence, with greater rotations occurring at higher loads. The muscle bulge increased with both the pedal cadence and load. The AGR had little change with load but did increase with faster cadences, this was particularly the case for the soleus muscle. The higher AGR at faster cadences enable the muscles to be mechanically effective across large range of speeds.