Eccentric exercise inhibits the H reflex in the middle part of the trapezius muscle.

The objectives of this study were to (1) investigate the modulation of the H reflex immediately after and 24 h after eccentric exercise in the presence of delayed-onset muscle soreness (DOMS) and (2) test the reproducibility of the H reflex in trapezius across days. H reflexes were recorded from the dominant middle trapezius muscle by electrical stimulation of the C3/4 cervical nerve in ten healthy subjects. DOMS was induced by eccentric exercise of the dominant shoulder. H reflexes were obtained in four sessions: '24 h before', 'Pre', 'Post', and '24 h after' eccentric exercise. Ratios of maximal H reflex and M wave responses ( H/ M) were compared between sessions. In addition, a between session comparison was done for the ratios of H reflex amplitudes ( H/ M, and H/ M) obtained from the stimulus intensity needed to obtain 75 and 50 % of H at '24 h before'. No ratio changes were found when comparing '24 h before' and 'Pre' recordings. A decrease in H/ M was found at 'Post' ( P < 0.05) and decreases in both H/ M and H/ M were observed at '24 h after' ( P < 0.05). This study presented evidence that an acceptable day-to-day reproducibility of the H reflex could be obtained with the applied experimental setup. Furthermore, immediately after and 24 h after exercise a stronger stimulus intensity was needed to reach the same magnitude of the H reflex reflecting that the recruitment curve was shifted to the right. This modulation of the stimulus-response relationship could be caused by presynaptic inhibition of Ia afferent fibres' input to the motoneuron by group III and IV afferents. [ABSTRACT FROM AUTHOR]