Time-dependent effects of pre-conditioning activation on muscle fiber conduction velocity and twitch torque.

In this study we investigate the range of interstimulus intervals influencing the recovery functions for conduction velocity (velocity recovery function, or VRF) and twitch torque (twitch torque recovery function, or TRF) of muscle fibers. We studied the tibialis anterior muscle of 8 healthy men by varying the time interval between a pair of stimuli in the range of 4-1000 ms, with (triplet) and without (doublet) a preconditioning stimulus. For triplet stimulations, the interval between the first and second stimulus or between the second and third stimulus was fixed, and the other interval was varied. VRF and TRF were influenced by a preconditioning stimulus only when it was delivered within 125 ms and 30 ms, respectively, before the doublet stimulation. The results provide evidence of the range of preconditioning intervals influencing the VRF and TRF; this is relevant for understanding the mechanisms of force generation and for standardizing compound action potential measurements.