An integrated model of rapid torque production: neuromuscular adaptations under fatigue after strength training

This study investigated the effects of short-term maximal strength training on the dynamics of maximal torque and torque impulse, assessed in non-fatigued and fatigued muscles across distinct temporal domains. Nineteen healthy men participated: ten performed a unilateral short-term training program of the knee extensors, while nine maintained their habitual routines as a control group. Before and after the intervention, all participants performed a 5-minute all-out test. The test was used to characterize the torque-time hyperbolic relationship and to determine critical torque (CT) and critical impulse (CI), as well as the accumulated impulse above CT and CI (iCT' and iCI'). In the non-fatigued condition, training significantly increased maximal torque (p = 0.040), with no changes in torque impulse or integrated electromyography (iEMG) across the 30, 100, and 200 ms time windows (all p > 0.05). During the 5-min all-out test, training significantly increased the time constant (τ) of the decay in maximal torque and total impulse of torque (all, p < 0.05), while CT and CI remained unchanged (all, p > 0.05). In parallel, iCT' and iCI' increased significantly (all, p < 0.05). Analysis of iEMG revealed an increase in the intercept of the iEMG-contraction relationship (p < 0.05), with no change in its slope (p > 0.05). These findings demonstrate that short-term maximal strength training enhances maximal torque and fatigue tolerance during sustained maximal efforts via slower neuromechanical decay and greater impulse availability above critical thresholds, without altering the critical limits of torque or impulse.