Blood flow restriction accelerates recruitment during a high-intensity non-volitional task

This study examined blood flow restriction (BFR) usage and motor unit (MU) behavior of the biceps brachii (BB) during a single high-intensity contraction. Twelve resistance-trained males (25±5 yrs) completed maximal voluntary isometric contractions (MVCs) of the elbow flexors, followed by a 70% MVC with (BFR) and without BFR (CON). Surface electromyographic (EMG) signals from the 70% MVCs were decomposed to extract MU: recruitment thresholds (RTs), action potential amplitudes (MUAP AMPS), and mean firing rates (MFRs). EMG amplitude (EMG RMS) at 70% MVC was normalized (N-EMG RMS) to MVC EMG RMS. Paired samples t-tests compared the y-intercepts and slopes of the MUAP AMP and MFR vs. RT relationships, and N-EMG RMS between treatments. For the MUAP AMP vs. RT relationships, the y-intercepts were greater (p=0.016) for CON than BFR, whereas the slopes were greater (p=0.024) for BFR than CON. For the MFR vs. RT relationships, the y-intercepts were greater (p=0.039) for BFR than CON, whereas the slopes were more negative (p=0.023) for BFR than CON. N-EMG RMS was greater (p=0.038) for BFR than CON. BFR accelerated higher-threshold MU recruitment, increased lower-threshold MU firing rates, and increased N-EMG RMS during a single high-intensity muscle action. BFR may be beneficial for accelerating MU recruitment in populations/scenarios where near-maximal efforts are contraindicated.