COMPARISON OF THE M. SOLEUS H-REFLEX DURING FATIGUE OF SYNERGIST AND ANTAGONIST MUSCLES

Abstract

Aim. The objective of this study was to investigate the impact of synergist and antagonist muscle fatigue on the H-reflex indicators of the soleus muscle, as well as to elucidate the characteristics of the H-response and M-response in response to varying intensities of tibial nerve stimulation. Materials and methods. The study utilized an electroneuromyograph (Neurosoft) to record the H-reflex indicators of the soleus muscle in a supine position in 25 healthy athletes. The recording was conducted before and during a 14-minute recovery period following a 5-minute fatigue protocol involving 30 seconds of exercise and 30 seconds of rest, targeting synergistic muscles (standing on tip toes) and antagonist muscles (toe raises) with two levels of tibial nerve stimulation: 80% of Nmax (n = 8) and 120% of Nmax (n = 15). Results. The findings revealed that the H-response of the soleus muscle experienced a consistent decrease in response to both synergist and antagonist muscle fatigue, but only at an intensity of 80% of Nmax. No changes in the H-response were observed with stimulation at 120% of Nmax. The recovery of the H-response post-maximum exercise was noted to occur within 3.5 minutes. Conversely, the M-response of the soleus muscle exhibited a decrease only in response to synergist muscle fatigue and at a stimulation intensity of 120% of Nmax, without changes observed in response to antagonist muscle fatigue. The recovery of the M-response post-maximum exercise on the soleus muscle synergists was only observed after 14 minutes of rest. Conclusion. Fatigue of both synergist and antagonist muscles leads to a temporary decrease in the H-response, indicative of reduced excitability of α-motor neurons and/or increased presynaptic inhibition of Ia-afferents to the soleus muscle. For the assessment of the H-response, it is advisable to use stimulation intensities below Hmax, whereas for evaluating the M-response, stimulation intensities exceeding Hmax are advised.