Repetitive eccentric muscle contractions increase torque unsteadiness in the human triceps brachii

Abstract

Torque steadiness and low-frequency fatigue (LFF) were examined in the human triceps brachii after concentric or eccentric fatigue protocols. Healthy young males (n = 17) performed either concentric or eccentric elbow extensor contractions until the eccentric maximal voluntary torque decreased to 75% of pre-fatigue for both (concentric and eccentric) protocols. The number of concentric contractions was greater than the number of eccentric contractions needed to induce the same 25% decrease in eccentric MVC torque (52.2 ± 2.9 vs. 41.5 ± 2.1 for the concentric and eccentric protocols, respectively, p < .01). The extent of peripheral fatigue was ~ 12% greater after the concentric compared to the eccentric protocol (twitch amplitude), whereas LFF (increase in double pulse torque/ single pulse torque), was similar across protocols. Steadiness, or the ability for a subject to hold a submaximal isometric contraction, was ~ 20 % more impaired during the Ecc protocol (p = .052). Similarly, the EMG activity required to hold the torque steady was nearly 20 %greater after the eccentric compared to concentric protocol. These findings support that task dependent eccentric contractions preferentially alter CNS control during a precision based steadiness task.

Evaluation of repetitive isometric contractions on the heads of triceps brachii muscle during grip force exercise

“…At the medial head, the RMS values were observed to increase in small amounts throughout the 5 isometric contractions. These findings concur with a previous study [13] which analysed the EMG RMS amplitude and median frequency of the EMG power spectrum on the medial head of the TB during different types of maximal voluntary isometric contractions. This previous study found that both the RMS amplitude and the median power frequency remained similar during a protocol which examined maximal voluntary isometric contractions before muscle fatigue, which is similar to the protocol used in our present study.…”

“…Furthermore, the author in [11] demonstrated that the TB is a long muscle on the posterior humerus which consists of a three-headed and fusiform arrangement, and operates as a third-class lever because force is applied between the joint axis and the load. Various sEMG findings associated with the TB and the processing methods used to analyse the TB have been focused on a large number of muscular activities, for example muscle fatigue [12][13][14][15], force [16,17], and motor unit action potential [18,19]. These activities of the TB are generally investigated because of their physiological importance in exercise [20][21][22], rehabilitation [23][24][25], sports science [26][27][28], and signal processing for prosthesis control applications [29][30][31].…”

Motor unit activity after eccentric exercise and muscle damage in humans

“…In this study, they showed that eccentric (but not concentric) exercise of the knee extensor muscles resulted in a change in the EMG-force relation, with a more-than-proportional increase in EMG during lowforce isometric contractions when performed immediately after and 2 days after eccentric exercise. This effect has since been confirmed for isometric contractions when performed immediately after eccentric exercise in other muscle groups such as the elbow flexors (Weerakkody et al 2003, Prasartwuth et al 2005, Semmler et al 2007, elbow extensors (Carson et al 2002, Meszaros et al 2010, wrist extensors (Leger & Milner 2001b) and intrinsic hand muscles (Leger & Milner 2001a). Furthermore, we have also shown this effect to be greatest in elbow flexor muscles during shortening contractions compared with isometric and lengthening contractions after eccentric muscle damage (Turner et al 2008).…”

Validade de um protocolo específico para análise de fadiga neuromuscular da musculatura extensora do cotovelo.

“…Dentre estes, é notável que grande parte dos estudos optam por avaliar o bíceps braquial (26,(31)(32)(33)(34) em função da notável dificuldade existente para interpretar algumas respostas neuromusculares da musculatura extensora de cotovelo (18,35,36).…”

“…Frequentemente utilizado no procedimento de avaliação da condição neuromuscular, a utilização de uma contração voluntária máxima (CVM), que é associada com uma estimulação a fim de verificar a condição da via central, pode promover alterações neuromusculares que proporcionem a musculatura extensora do cotovelo estados como fadiga central (18,38), fadiga periférica (35) ou aumento da resposta muscular em função do aumento de ativação muscular (16), enviesando a avaliação.…”