Peak power is elevated in slow and fast‐twitch muscle fibers from competitive distance runners

Abstract

The purpose of this study was to characterize the influence of a long‐term (8‐yr) history of high‐intensity endurance training on the contractile properties of slow‐ and fast‐twitch myofibers. Muscle biopsies were obtained from 8 competitive distance runners (RUN) and 8 recreationally active individuals (REC). Slow‐twitch (MHC I) and fast‐twitch (MHC IIa) myofibers were analyzed for diameter, peak force (Po), contractile velocity (Vo), and power. MHC I and MHC IIa fibers from RUN subjects were ~20% larger (P<0.05) than REC. Peak force of the MHC IIa fibers was 31% higher (P<0.05) in RUN while Po of MHC I fibers was not different between groups. No differences for specific tension (Po/CSA) were present between groups for either fiber type. Vo was higher (P<0.05) in MHC I (+70%) and MHC IIa (+18%) fibers from RUN subjects. Peak absolute power of both fiber types was greater (P<0.05) in RUN. Normalized power of the MHC I fibers was 64% higher in RUN while no differences were noted for MHC IIa fibers. These data suggest that performing long‐duration endurance training modifies myofiber contractile function, resulting in higher peak power production of slow‐ and fast‐twitch fibers. Furthermore, these data suggest that long‐term training may result in adaptations in contractile physiology that are more pronounced than alterations previously observed in short‐term exercise interventions.