Neurophysiological Responses After Short-Term Strength Training of the Biceps Brachii Muscle

Abstract

The neural adaptations that mediate the increase in strength in the early phase of a strength training program are not well understood; however, changes in neural drive and corticospinal excitability have been hypothesized. To determine the neural adaptations to strength training, we used transcranial magnetic stimulation (TMS) to compare the effect of strength training of the right elbow flexor muscles on the functional properties of the corticospinal pathway. Motor-evoked potentials (MEPs) were recorded from the right biceps brachii (BB) muscle from 23 individuals (training group; n = 13 and control group; n = 10) before and after 4 weeks of progressive overload strength training at 80% of 1-repetition maximum (1RM). The TMS was delivered at 10% of the root mean square electromyographic signal (rmsEMG) obtained from a maximal voluntary contraction (MVC) at intensities of 5% of stimulator output below active motor threshold (AMT) until saturation of the MEP (MEPmax). Strength training resulted in a 28% (p = 0.0001) increase in 1RM strength, and this was accompanied by a 53% increase (p = 0.05) in the amplitude of the MEP at AMT, 33% (p = 0.05) increase in MEP at 20% above AMT, and a 38% increase at MEPmax (p = 0.04). There were no significant differences in the estimated slope (p = 0.47) or peak slope of the stimulus-response curve for the left primary motor cortex (M1) after strength training (p = 0.61). These results demonstrate that heavy-load isotonic strength training alters neural transmission via the corticospinal pathway projecting to the motoneurons controlling BB and in part underpin the strength changes observed in this study.

Reliability and smallest worthwhile difference in 1RM tests according to previous resistance training experience in young women

“…One possibility might involve the nervous system where adaptations can occur quickly. Increases in motor-unit recruitment, rate coding of motor units, improved synergistic muscle contribution, and reductions in the coactivation of antagonists muscles might promoted increases in muscular strength between sessions [32][33][34]. Moritoni and deVries [35] were among the first to indicate that neurological factors might play a significant role in the early increases in strength performance.…”

“…This phenomenon has been termed neural disinhibition [35,36] or autogenic inhibition [37] and is theorized to reduce the inhibitory function of Golgi tendon organs (GTO) to allow greater force output from muscle. Thus, the restrictive function of GTO on muscle contraction may be reduced when participants are subjected to repeated episodes of maximal muscular contraction [33][34][35][36][37]. In their review, Gabriel, Kamen, and Frost [33] discussed the possibility of an increased rate of motor unit activation early in RT which could account for enhanced muscular force and the slight increase in 1RM performance with successive trials.…”

“…Several previous studies have noted acceptable reliability for BP [7,11,14,[34][35][36][37], although less reliability information is available for SQ [7,11,13,36,37] and AC [36,37]. These are major lifts utilized for evaluating specific muscle groups and widely used in research and training.…”

Capacidade de repetição da força: efeito das recuperações interséries

“…As alterações fisiológicas, especialmente bioenergéticas e neuromusculares que provocam a fadiga, são expressas pela incapacidade das fibras em gerar força e pela diminuição da velocidade de encurtamento [33][34]37,[44][45][46] . No entanto, não é bem conhecida a importância de cada um desses aspectos no surgimento da fadiga [47][48][49] . Porém, sabe-se que estas alterações funcionais afetarão, em maior ou menor grau, o desempenho esportivo e a qualidade do gesto motor (FIGURA 4).…”

Intensity-dependent effects of cycling exercise on corticospinal excitability in healthy humans: a pilot study

“…However, great variations among exercise modalities in the amount of muscle work, and the consequent cardiorespiratory demands and other factors such as cerebral oxygenation consumption rate may also explain the differential corticospinal responses after dynamic vs. static exercise 5,7 . There have been some reports in which transcranial magnetic stimulation (TMS) has been used to test the effects of physical exercise on corticospinal excitability 8,9 . Its effects on the responsiveness of corticospinal cells appear to be dependent on the type of exercise (dynamic vs static) 5,8 .…”