Neuromuscular fatigue following isometric contractions with similar torque time integral.

J Theurel,R Lepers,T Cattagni,A Martin,V Rozand

doi:10.1055/s-0034-1375614

J Theurel, R Lepers + Show 3 more

Open Access

https://doi.org/10.1055/s-0034-1375614

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Abstract

Torque time integral (TTI) is the combination of intensity and duration of a contraction. The aim of this study was to compare neuromuscular alterations following different isometric sub-maximal contractions of the knee extensor muscles but with similar TTI. Sixteen participants performed 3 sustained contractions at different intensities (25%, 50%, and 75% of Maximal Voluntary Contraction (MVC) torque) with different durations (68.5±33.4 s, 35.1±16.8 s and 24.8±12.9 s, respectively) but similar TTI value. MVC torque, maximal voluntary activation level (VAL), M-wave characteristics and potentiated doublet amplitude were assessed before and immediately after the sustained contractions. EMG activity of the vastus lateralis (VL) and -rectus femoris (RF) muscles was recorded during the sustained contractions. MVC torque reduction was similar in the 3 conditions after the exercise (-23.4±2.7%). VAL decreased significantly in a similar extent (-3.1±1.3%) after the 3 sustained contractions. Potentiated doublet amplitude was similarly reduced in the 3 conditions (-19.7±1.5%), but VL and RF M-wave amplitudes remained unchanged. EMG activity of VL and RF muscles increased in the same extent during the 3 contractions (VL: 54.5±40.4%; RF: 53.1±48.7%). These results suggest that central and peripheral alterations accounting for muscle fatigue are similar following isometric contractions with similar TTI. TTI should be considered in the exploration of muscle fatigue during sustained isometric contractions.

Highlights

Voluntary sustained sub-maximal contractionsmaximal voluntary contraction (MVC)) level of contraction [13, 39]
The results showed that the level of muscle fatigue quantified by MVC torque loss was similar (̴ 25 %) after sustained contractions with similar Torque time integral (TTI) despite different intensity-duration combination
Studies which observed a higher central fatigue after low-inten- In practical application our results suggest that the TTI method, sity contractions compared to high intensities [5, 39], the con- which quantifies the physical work, could be used as a completractions performed at 25 %, 50 % and 75 % MVC induced the mentary approach in strength training programs to control same amount of central fatigue

Summary

Introduction

In these studies the underlying mechanisms responsible for the decrease in MVC were differlead to neuromuscular fatigue, characterized by a ent. Fuglevand et al [13] observed a accepted after revision March 25, 2014 decrease in maximal voluntary contraction (MVC) force [8, 20, 31]. Neuromuscular fatigue can be defined as an exercise-induced reduction greater peripheral fatigue E., a reduction of muscle twitch amplitude and M-wave amplitude) following low-intensity contraction Neuromuscular fatigue can be defined as an exercise-induced reduction greater peripheral fatigue (i. e., a reduction of muscle twitch amplitude and M-wave amplitude) following low-intensity contraction

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