Behavior of coactive muscles during fatigue

Abstract

Coactivation is antagonist muscle activity that occurs during voluntary contraction. Recently, we showed that the extent of coactivity in the knee flexors decreases after a short period of resistance training of the knee extensors (8). The purpose of the present experiment was to study the time course of coactivation in the knee flexors during fatigue of the knee extensors. Ten male subjects performed repeated submaximal static leg extensions in a low-intensity long-duration and a high-intensity short-duration fatigue protocol until they could no longer produce the required force [time limit of endurance (Tlim)]. Maximal voluntary contraction (MVC), submaximal force, and surface electromyographic (EMG) activity were measured periodically. Vastus lateralis EMG increased progressively during fatigue of the extensor muscles (P < 0.05), resulting in a 38% change from control at Tlim. Biceps femoris EMG, which was our measure of coactivation, also increased by approximately 60% at Tlim in each protocol (P < 0.05). These observations lead us to conclude that a small but significant force loss during repeated static contractions to Tlim is due to an increase in antagonist activity. Moreover, the close correlation between the antagonist and agonist EMG supports the notion of a "common drive" to both motoneuron pools (10).

Postural after‐contractions in man attributed to muscle spindle thixotropy

“…As pointed out by several investigators (Jahnke et al 1989;Proske et al 1993;Nordin & Hagbarth, 1996) the after-effects of a conditioning isometric voluntary contraction are highly dependent on the unconditioned state of the muscle, in which the stiffness or slackness of both extra-and intrafusal muscle fibres at any given time may vary as a result of thixotropic after-effects which remain after preceding movements andÏor contractions. It has previously been demonstrated that antagonistic muscles are co-activated during forceful voluntary isometric contractions of a given muscle group (Psek & Cafarelli, 1993). Thus, it is probable that in the present experiments the forceful hold-short arm abductor contractions were also accompanied by contractions in the arm adductors for which the conditioning contractions were of the 'hold-long' type.…”

Bilateral motor unit synchronization is functionally organized

“…Indeed, several studies have shown that the force generating capacity of the antagonist muscles remained equal after fatiguing contractions of the agonist muscles (e.g., Levenez et al 2005). Although the eVects on the EMG amplitude and median frequency of the antagonist muscle could, in principle, result from cross-talk, it is typically interpreted as an eVect of a common drive to the agonist-antagonist couple (Psek and Cafarelli 1993;Ebenbichler et al 1998;Mullany et al 2002;Levenez et al 2005). In support of this interpretation, an increase in amplitude and a decrease in median frequency have been found in the contralateral homologous muscle after unilateral muscle fatigue (Morrison et al 2005).…”

Respostas neuromusculares dos membros inferiores durante protocolo intermitente de saltos verticais em voleibolistas

“…Outra possível relação que poderia ser realizada como forma de compreensão dos resultados obtidos trata-se da coativação (Weir et al, 1998;. Psek;Cafarelli;, a qual consiste na atividade do músculo antagonista durante contração voluntária.…”

“…Psek;Cafarelli;, a qual consiste na atividade do músculo antagonista durante contração voluntária. A coativação muscular dos flexores do joelho durante fadiga de seus extensores demonstra que um aumento da força dos isquiotibiais pode diminuir a força produzida pelo quadríceps (WEIR et al, 1998).…”

“…Ainda, segundo Psek;Cafarelli (1993), a forte correlação da atividade EMG entre o VL e BF durante fadiga é consistente com a noção de um mediador de saída motora central comum para o par agonista-antagonista. Neste estudo, foi utilizado como representante dos extensores do joelho o músculo RF e como o antagonista o BF.…”