W' reconstitution rate at different intensities above critical torque: the role of muscle size and maximal strength.

Muscle perfusion and O2 delivery limitations through muscle force generation appear to play a major role in defining the hyperbolic torque-time to task failure (Tlim ) relationship. Therefore, we aimed to determine the influence of muscle size and maximal strength on the recovery time constant for the finite impulse above critical torque (τIET' ). Ten men participated in the study and performed intermittent isometric tests until task-failure (Tlim ) for the knee-extensors (KE) (35% and 60% maximal voluntary contraction (MVC)) and plantar flexors (PF) (60% MVC). The τIET' was determined for each of these Tlim tests using the IET'BAL model. The IET' (9738 ± 3080 vs. 2959 ± 1289 N m s) and end-test torque (ET)(84.5 ± 7.1 vs. 74.3 ± 12.7 N m) were significantly lower for PF compared to KE (P < 0.05). Exercise tolerance (Tlim ) was significantly longer for PF (239 ± 81 s) than KE (150 ± 55 s) at 60% MVC, and significantly longer for KE at 35% MVC (641 ± 158 s) than 60% MVC. The τIET' was significantly faster at 35% MVC (641 ± 177 s) than 60% MVC (1840 ± 354 s) for KE, both of which were significantly slower than PF at 60% MVC (317 ± 102 s). This study showed that τIET' during intermittent isometric exercise is slower with greater muscle size and maximal strength.