Effect of voluntary contraction with electrical stimulation antagonist muscle on agonist H-reflex

Objective: Hybrid exercise (HE) was designed to use the force generated by an electrically stimulated antagonist to provide resistance to a volitionally contracting agonist. The purpose of this study was to measure and compare the soleus H-reflex before and after HE or conventional resistance exercise (CRE). Methods: The experiments were carried out in 18 healthy subjects (5 men and 13 women; 19-30 yr), who were divided into 2 groups of 9 for each protocol (HE or CRE). The exercise sessions lasted for 15 consecutive minutes. The soleus H_max/M_max was measured before and after the HE or the CRE. Results: In the HE group, although there was no significant difference, the soleus H_max/M_max after the exercise increased compared with before the exercise (54.7 ± 10.2% to 59.0 ± 14.5%). On the other hand, the soleus H_max/M_max decreased in the CRE group (61.8 ± 14.9% to 55.7 ± 16.1%). In the rate of change of the soleus H_max/M_max, the result for the HE group was significantly higher than in the CRE group (108.0 ± 11.7% and 89.1 ± 8.0%, respectively) (p < 0.001). Conclusion: Our results show a clear difference of the neurophysiological mechanism between HE and CRE. Thus, HE might not be an alternative method for CRE.