SPRINT TRAINING, IN-VITRO AND IN-VIVO MUSCLE FUNCTION, AND MYOSIN HEAVY-CHAIN EXPRESSION

Sprint training represents the condition in which increases in muscle shortening speed, as well as in strength, might play a significant rol e in improving power generation. This study therefore aimed to determi ne the effects of sprint training on 1) the coupling between myosin he avy chain (MHC) isoform expression and function in single fibers, 2) t he distribution of MHC isoforms across a whole muscle, and 3) in vivo muscle function. Seven young male subjects completed 6 wk of training (3-s sprints) on a cycle ergometer. Training was without effect on max imum shortening velocity in single fibers or in the relative distribut ion of MHC isoforms in either the soleus or the vastus lateralis muscl es. Electrically evoked and voluntary isometric torque generation incr eased (P < 0.05) after training in both the plantar flexors (+8% at 50 Hz and +16% maximal voluntary contraction) and knee extensors (+8% at 50 Hz and +7% maximal voluntary contraction). With the shortening pot ential of the muscles apparently unchanged, the increased strength of the major lower limb muscles is likely to have contributed to the 7% i ncrease (P < 0.05) in peak pedal frequency during cycling.