The Rate of Torque Development as a Determinant of the Torque-Velocity Relationship

We investigate the contribution of isometric rate of torque development (RTD) and maximal voluntary torque (MVT) to the dynamic force production capacities of knee extensors obtained from the torque-velocity (TV) relationship, that is, the theoretical maximal velocity (V₀), torque (T₀), and maximal power (P_max). Single-leg knee extensors were tested in 64 young adults (31 females). RTD and root mean square (RMS) of electromyographic signals from the knee extensors were recorded during isometric and incremental load dynamic (nonisokinetic) contractions. In the dynamic test, torque and velocity were continuously measured and averaged over 80°-140° knee angles to determine individual TV relationships. TV relationships were well fitted by hyperbolic regression (r² from 0.983 to 0.993). Stepwise linear regressions showed that the main determinant of V₀ was normalized RTD50 (R² = 0.145, p = 0.004); the main determinant of T₀ was MVT (R² = 0.760, p < 0.001); and the main determinant of P_max was RTD150 (R² = 0.612, p < 0.001). V₀ (when obtained from averaged values over knee extension) is partially explained by rapid torque capacity (i.e., "explosive strength"). Therefore, the capacity to produce torque at high velocity partly depends on the capacity to rise quickly the torque in the early phase of the contraction, suggesting that some underlying determinants of RFD would also affect V₀.