Doctor of Philosophy
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.
Summary for Lay Audience
Blood flow occlusion (BFO) or the removal of blood flow, can be used to enhance muscle and central nervous system fatigue when combined with low-intensity contractions. The use of BFO with low-intensity contractions has been observed to increase muscle growth (hypertrophy) and muscle strength when incorporated into long-term resistance training programs. The goal of the four studies presented within this thesis sought to explore the short-term effects of BFO on muscle and central nervous system fatigue.
Experiment one investigated whether BFO with a low-intensity contractions to exhaustion (unable to maintain muscle contraction) of the muscles that produce flexion of the arm cause greater muscle fatigue compared to the same contraction with normal blood flow. The results indicate that BFO caused greater fatigue in a reduced amount of time. This indicates that BFO can shorten overall time required to produce greater muscle changes during exercise.
Experiment two explored changes in the central nervous system during a low-intensity contraction of the arm flexors with and without BFO. The experiment found BFO caused greater changes within the central nervous system in a shorter amount of time. This indicates that BFO causes changes within the brain and spinal cord that are different than contractions performed with normal blood flow.
Experiment three investigated whether BFO during low-intensity arm flexor contractions to exhaustion produced greater amounts of muscle fatigue, as well as reduced the speed of contracting muscles compared to a high-intensity bout of contractions with normal blood flow. Results showed low-intensity exercise with BFO produced greater muscle fatigue and greater reductions in muscle speed.
Experiment four investigated the changes in how muscle fibers activated when BFO is applied either above or below a working muscle. Results indicate when BFO was above the working muscle (no inward blood flow) muscle fibers decreased their rate of activation as the muscle became more fatigued, and this was more than when the outflow of the working muscle (below) was occluded.
The results of these experiment indicate that occlusion of blood flow changes how muscles activated and fatigued, when compared to contractions of muscle during normal blood free flow.
Copithorne, David B., "Impacts of blood flow occlusion on the human neuromuscular system" (2019). Electronic Thesis and Dissertation Repository. 6291.