Recovery pattern of motor reflex after a single bout of neuromuscular electrical stimulation session

We aimed at determining the recovery pattern of neural properties of soleus muscle after a single bout of neuromuscular electrical stimulation (NMES) session. Thirteen subjects performed an NMES exercise (75 Hz, 40 contractions, 6.25 s per contraction). Maximal voluntary contraction (MVC), H-reflex at rest and during voluntary contraction fixed at 60% of MVC (respectively, Hmax and Hsup) and volitional (V) wave were measured before and during the recovery period following this exercise [i.e., immediately after, 2 h (H2), 2 days (D2) and 7 days (D7)]. MVC exhibited an immediate and a delayed declines at 2 days (respectively, -29.8 +/- 4.6%, P<0.001; -13.0 +/- 3.4%, P<0.05). Likewise, V/Msup was decreased immediately and 2 days after NMES session (respectively, -43.3 +/- 11.6%, P<0.05; 35.3 +/- 6.6%, P<0.05). The delayed decrements in MVC and V-wave occurred concomitantly with muscle soreness peak (P<0.001). It could be concluded that motor command alterations after an NMES resistance session contributed to the immediate and also to the delayed decreases in MVC without affecting resting and active H-reflex excitability. These results suggested that spinal circuitry function of larger motoneurons was inhibited by NMES (as indicated by the depressed V-wave responses) contrary to the smaller one (indicated by the unchanged H-reflex responses).