The effects of training status and recovery time on the reconstitution of impulse above electrically stimulated critical torque

Fatigue represents a reduction in the desired or expected muscular force (Porter, 1981) often as a result of intense or prolonged exercise. Critical power (CP) provides a framework to understand fatigue and exercise intolerance, in that it represents a threshold power output below which it is possible to maintain steady-state exercise. Above CP time-to-exhaustion occurs in a predictable manner often termed the “power-duration relationship” whereby the higher the work rate is above CP, the shorter the exercise duration. W’ represents the curvature constant for work performed above CP. It represents a fixed amount of total work that can be performed before fatigue is reached. Little is known about W’ reconstitution and its rate (kinetics) of recovery during and following exercise, but has been linked to the recovery of muscle phosphocreatine concentrations and state of aerobic training. No data exist on the kinetics of W’ reconstitution using isometric contractions where it is termed impulse above critical torque (IACT) and the extent to which it is affected by training state and peripheral fatigue. The purpose of this study was to examine the time-course of the reconstitution of IACT’ following its depletion during electrically evoked isometric exercise examine the effects of aerobic training status on IACT reconstitution. Twenty six participants (10 trained, 16 untrained) completed 4 bouts of electrically stimulated exercise consisting of 75 contractions using a 2-sec:2-sec on/off duty cycle of the knee extensors. IACT was calculated as the sum of the area under the torque-time curve above the critical torque (CT) across all contractions; determined as the average of the final 6 contractions. Five or 15 minutes of rest was provided and then exercise as repeated. A mixed methods ANOVA revealed the three-way interaction among rest period (5-min vs. 15-min), exercise bout (1st or second on that day), and training status was not significant (p=0.79). A significant (p < 0.001) main effect for exercise bout was found with values from bout 2 being reduced (~21%) compared to round 1 to a similar extent regardless of training status or rest provided. The findings of this study are in contrast to previous studies that found that additional rest and higher aerobic training status lead to faster recovery of W’/IACT. Our findings clearly indicate that peripheral occurs during exercise and that it does not recovery, even when 15-min of rest are provided