Enhanced H-reflex with resistance training is related to increased rate of force development

Abstract

Parallel increases in strength and rate of force development (RFD) are well-known outcomes from the initial phase of resistance training. However, it is unknown whether neural adaptations with training contribute to improvements of both factors. The aim of this study was to examine whether changes in H-reflex amplitude with resistance training can explain the gain in strength or rather be associated with RFD. Twelve subjects carried out 3 weeks of isometric maximal plantarflexion training, whereas 12 subjects functioned as controls. H-reflexes were elicited in the soleus muscle during rest and sub-maximal contractions at 20 and 60% of maximal voluntary contraction (MVC). In addition, surface electromyography (sEMG) was recorded from the soleus, gastrocnemius and tibialis anterior muscles during MVC. The resistance training provided increases in maximal force of 18%, RFD of 28% and H-reflex amplitude during voluntary contractions of 17 and 15% while no changes occurred in the control group. In contrast, the maximal M-wave, the maximal H-reflex to maximal M-wave ratio during rest and sEMG during MVC did not change with training. There was a positive correlation between percentage changes in H-reflex amplitude and RFD with training (r = 0.59), while significant association between percentage changes in H-reflex amplitude and maximal force was not found. These findings indicate the occurrence of changed motoneuron excitability or presynaptic inhibition during the initial phase of resistance training. This is the first study to document that increased RFD with resistance training is associated with changes in reflex excitability.

Effect of an Acute Bout of Whole Body Vibration Exercise on Muscle Force Output and Motor Neuron Excitability

“…The receiving electrode (Noraxon USA, Inc., Scottsdale, AZ; 2-cm interelectrode distance, 1 cm 2 circular conductive area) on the soleus muscle was positioned approximately 13 cm above the superior portion of the calcaneus and below the muscle fibers of the gastrocnemius (1). A remote stimulus device (Nicolet Viking II; Nicolet Biomedical, Madison, WI) was then used to locate the optimal site for stimulation of the tibial nerve (18). After the optimal site was determined, a bipolar stimulating electrode (1-cm conduction area and 3-cm interelectrode distance) was secured in the same area using adhesive tape.…”

“…PAP is a condition in which pre-exercise muscle contractions lead to subsequent enhanced muscle force output through either increased motor neuron excitability or phosphorylation of myosin light chains (13,17,22,26). Motor neuron excitability has been measured indirectly by utilizing a technique involving tibial nerve stimulation in many investigations (3,11,15,18,21,27). Two electromyographic wave patterns appear during this technique.…”

“…Two electromyographic wave patterns appear during this technique. The M wave is a single twitch of the electrically stimulated muscle, and the H reflex is a wave pattern resulting from activation of a monosynaptic reflex response as a result of electrical stimulation to the same muscle (18). Expressing the H-reflex wave amplitude with respect to the M-wave amplitude allows for a ratio indicative of the motor neuron excitability (18).…”

“…The stimuli were delivered as 1-millisecond square pulses without simultaneous contraction of the triceps surae complex. Starting at a stimulus of 3 V, the stimuli were administered in 3-V increments at a rate of 0.1 Hz (18) until no further visual increase in the peak-to-peak M-wave amplitude was detected (1,18 …”

Avaliação da inibição recíproca em humanos durante contrações isométricas dos músculos tibial anterior e sóleo

“…Isso foi verificado em um estudo com a depressão do RH do M. sóleo durante a DF, que ocorreu antes do início do sinal eletromiográfico do mús-culo tibial anterior 15 , ou seja, sem influência das fibras aferentes. Além disso, em outro estudo, o bloqueio periférico do nervo fibular comum (NFC), por aplicação de lidocaína, também não impediu que o RH do sóleo sofresse grande depressão durante a DF fictícia 14 18 observaram que o treinamento resistido de flexores plantares promoveu um aumento na força muscular e na amplitude do reflexo H do sóleo, sugerindo mudanças na excitabilidade dos motoneurônios e na inibição pré-sináptica.…”