Effect of blood flow occlusion on corticospinal excitability during sustained low-intensity isometric elbow flexion.

Blood flow occlusion (BFO) has been used to study the influence of group III/IV muscle afferents after fatiguing exercise, but it is unknown how BFO-induced activity of these afferents affects motor cortical and motoneuronal excitability during low-intensity exercise. Therefore, the purpose of this study was to assess the acute effect of BFO on peripheral [maximal M wave (M)], spinal [cervicomedullary motor evoked potential (CMEP) normalized to M], and motor cortical [motor evoked potential (MEP) normalized to CMEP] excitability. Nine healthy men completed a sustained isometric contraction of the elbow flexors at 20% of maximal force under three conditions: ) contractile failure with BFO, ) a time-matched trial without restriction [free flow (FFiso)], and ) contractile failure with free flow (FFfail). Time to failure for BFO (and FFiso) were ~80% shorter than that for FFfail ( < 0.05). For FFfail and FFiso, M area decreased ~17% and ~7%, respectively ( < 0.05), with no change during BFO. CMEP/M area increased ~226% and ~80% during BFO and FFfail, respectively ( < 0.05), with no change during FFiso ( > 0.05). The increase in normalized CMEP area was greater for BFO and FFfail compared with FFiso and for BFO compared with FFfail. MEP/CMEP area was not different among the protocols ( > 0.05) and increased ~64% with time ( < 0.05). It is likely that group III/IV muscle afferent feedback to the spinal cord modulates the large increase in motoneuronal excitability for the BFO compared with FFfail and FFiso protocols. We have observed how blood flow occlusion modulates motor cortical, spinal, and peripheral excitability during and immediately after a sustained low-intensity isometric elbow flexion contraction to failure. We conclude that blood flow occlusion causes a greater and more rapid increase in motoneuronal excitability.