Central alterations of neuromuscular function and feedback from group III-IV muscle afferents following exhaustive high-intensity one-leg dynamic exercise

The aims of this investigation were to describe the central alterations of neuromuscular function induced by exhaustive high intensity one leg dynamic exercise (OLDE, study 1), and to indirectly quantify feedback from group III-IV muscle afferents via muscle occlusion (MO, study 2) in healthy adult male humans. We hypothesized that these central alterations and their recovery are associated with changes in afferent feedback. Both studies consisted of two time to exhaustion tests at 85% peak power output. In study 1, voluntary activation level (VAL), M-wave (M), cervicomedullary motor evoked potential (CMEP), motor evoked potential (MEP) and MEP cortical silent period (CSP) of the knee extensor muscles were measured. In study 2, mean arterial pressure (MAP) and leg muscle pain were measured during MO. Measurements were performed pre-exercise, at exhaustion and after three minutes recovery. Compared to pre-exercise values, VAL was lower at exhaustion (-13±13%, P<0.05) and after three minutes recovery (-6±6%, P=0.05). CMEParea/Marea was lower at exhaustion (-38±13%, P<0.01) and recovered after three minutes. MEParea/Marea was higher at exhaustion (+25±27%, P<0.01) and after three minutes recovery (+17±20%, P<0.01). CSP was higher (+19±9%, P<0.01) only at exhaustion and recovered after three minutes. Markers of afferent feedback (MAP and leg muscle pain during MO) were significantly higher only at exhaustion. These findings suggest that the alterations in spinal excitability and CSP induced by high intensity OLDE are associated with an increase in afferent feedback at exhaustion, whilst central fatigue does not fully recover even when significant afferent feedback is no longer present.