Impacts of blood flow occlusion on the human neuromuscular system
Blood flow restricted or occlusion (BFO) exercise uses external pressure to impede blood flow, thus reducing the amount of oxygenated blood reaching the muscle, with greater pressure causing greater obstruction of blood flow. The result is enhanced muscle fatigability. The four studies in this thesis investigate how BFO acutely affects muscle fatigue, the neuromuscular system, muscle contractile properties and motor unit firing rates, using a combination of electrical stimulation, transcranial magnetic stimulation, transmastoid stimulation, force production, and electromyography (EMG). Study one investigated whether BFO low-intensity isometric contractions to failure of the arm flexors elicits greater muscle fatigue compared to low-intensity contraction with free blood flow. Results showed that BFO created a greater amount of low-frequency fatigue in a significantly reduced amount of time, but recovers at a normal rate once blood flow is restored. This indicates that BFO can reduce overall time required to produce greater amounts of muscle adaptations. Study two explored modulation of corticospinal tract excitability during low-intensity isometric arm flexion with and without BFO. The study found that BFO enhanced motoneurone excitability in a lesser amount of time to muscle failure. This likely indicates that BFO enhances excitability of the motoneurone possibly through a feedback loop activated by type III and IV muscle receptors. Study three investigated whether BFO low-intensity dynamic arm flexion to failure produced similar or greater amounts of muscle fatigue, as well as reduced power output, compared to high-intensity normal blood flow. The particular novelty was to explore dynamic actions rather than isometric. Results showed low-intensity exercise with BFO produced greater low-frequency fatigue and greater reductions in power. Therefore likely enhancing the requirement of the muscle adaptation. Study four investigated the modulation of motor unit firing rates (MUFRs) with BFO either distal or proximal to the tibialis anterior muscle. Results indicate when BFO was proximal MUFRs decreased as the muscle became more fatigued, and more than when flow was occluded distally, and both being more than control. This indicates that blood flow obstruction either proximal or distal to working muscle affects muscle fatigue greater than with free blood flow. Overall these investigations expand our knowledge of the acute effects of BFO, and can be extrapolated to factors responsible to long term training adaptations with blood flow restriction.
blood flow restriction, muscle, fatigue, transcranial magnetic stimulation, transmastoid electrical stimulation, electromyography, motor unit
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