Correlation between contractile strength and myosin heavy chain isoform composition in human skeletal muscle

Purpose: The purpose of this study was to investigate the relationship between myosin heavy chain (MHC) composition and maximal contraction strength of the human quadriceps femoris muscle, Methods: Muscle biopsies were obtained from m. vastus lateralis in young highly physical active males (N = 7). The MHC composition of muscle homogenates was determined by electrophoresis techniques (SDS-PAGE). Isokinetic peak torque and constant angle torque (50 degrees knee flexion) were obtained during slow (30 degrees . s(-1), medium (120 degrees . s(-1)), and fast (240 degrees . s(-1)) maximal concentric and eccentric quadriceps contractions and expressed relative to muscle volume. Results: The percentage of MHC II in the quadriceps muscle was positively correlated (r(s) = 0.61-0.93; P < 0.05-0.01) to maximal concentric quadriceps strength obtained at medium to high knee angular velocity. In contrast, no consistent pattern of correlation was observed for maximal eccentric quadriceps strength. Conclusions: The relationship observed between muscular MHC composition and maximal contractile strength is suggested to appear as a consequence of MHC-related differences in contractile force-velocity characteristics and/or contractile Rate of Force Development (RFD).