Twitch potentiation induced by stimulated and voluntary isometric contractions at various torque levels in human knee extensor muscles

Abstract

The purpose of this study was to compare the extent of twitch potentiation (TP) after stimulated or voluntary contractions at identical intensities for the human knee extensor muscles. Isometric knee extensions of 10 s were performed at 20%, 40%, and 60% of maximal voluntary contraction (MVC) torque level, through percutaneous electrical stimulation of the quadriceps at 80 Hz or voluntary contraction. Twitch responses were evoked by stimulating the femoral nerve percutaneously with supramaximal intensity. The extent of TP after the stimulated contraction was greater than that after the voluntary contraction at the 20% MVC torque level, whereas a stimulated contraction induced a smaller extent of TP than did a voluntary contraction at contraction intensities higher than 40% MVC. We suggest that this contraction intensity dependence of differences in TP after stimulated and voluntary isometric conditioning contractions is responsible for differences in the recruitment pattern of motor units during the conditioning contractions.

Potentiation of Maximal Voluntary Concentric Torque in Human Quadriceps Femoris

“…Namely, although submaximal contractions have so far been used as warm-up procedures to reduce fatigue, the current results indicate that high-intensity short-duration contractions can be a more effective warm-up modality for high-power activities. In addition, considering the present fmdings with our previous results (22,25), we can recommend the use of NMES with proper duration, intensity, and stimulation frequency as a more immediately effective warm-up modality for explosive sports activities. Furthermore, the current fmdings can provide an evidence for the effectiveness of complex training, which has been defined as combining plyometric and weight resistance exercises in the same training session, and help to establish proper protocols (i.e., rest interval between plyometdc and weight resistance exercises) in this training style.…”

“…3). This observation seems to be puzzling because the extent of TP is influenced by the number and fype of muscle fibers recmited during conditioning contractions (17,25,40). However, the difference in target torque levels does not necessarily correspond with that in the number of muscle fibers recruited.…”

“…T he joint torque generated by twitch contraction is increased after brief conditioning contractions performed voluntarily (17,24,40) and percutaneously evoked (22,25,31). This phenomenon is collectively called "twitch potentiation" (TP).…”

Twitch potentiation after voluntary contraction and neuromuscular electrical stimulation at various frequencies in human quadriceps femoris

“…The joint torque generated by twitch contraction is increased after brief voluntary 1–3 and stimulated contractions 4–6. This phenomenon is collectively referred to as twitch potentiation (TP).…”

“…Only a few investigations have compared the extent of TP elicited after voluntary and NMES at high‐stimulation‐frequency (80–100 H Z ) conditioning contractions at equivalent target levels. 4, 14, 15 Requena et al compared the extent of TP after voluntary vs. NMES contractions at 25% of maximal voluntary contraction (MVC) torque level, and demonstrated that the extent of TP after a 7‐s NMES at 100 H Z was greater than that after a 7‐s voluntary contraction in knee extensor muscles 15. In contrast, Jubeau et al showed that a 10‐s NMES of the quadriceps femoris at 100 H Z with 40% MVC torque induced a smaller TP than a 10‐s voluntary contraction 14.…”