Blood flow restriction increases motor unit firing rates and input excitation of the biceps brachii during a moderate-load muscle action

This study examined the effects of blood flow restriction (BFR) on motor unit (MU) behaviour of the biceps brachii (BB) during a single non-exhausting submaximal muscle action. Twenty adults performed maximal voluntary contractions (MVCs) of the elbow flexors, followed by an isometric trapezoidal muscle action at 40% MVC during BFR and control (CON) visits. Surface electromyographic signals recorded from the BB during the 40% MVCs were decomposed. Recruitment thresholds (RTs), MU action potential amplitudes (MUAP_AMPS), initial firing rates (IFRs), mean firing rates (MFRs) at steady force, and normalized EMG amplitude (N-EMG_RMS) were analysed. Y-intercepts and slopes were calculated for the MUAP_AMP, IFR, and MFR vs. RT relationships. Y-intercepts for the IFR and MFR vs. RT relationships and N-EMG_RMS increased during BFR (p < 0.05) collapsed across sex. The slopes for the IFR and MFR vs. RT relationships decreased during BFR (p < 0.05) collapsed across sex. The y-intercepts and slopes for the MUAP_AMP vs. RT relationships were not different (p > 0.05) between treatments or sex. BFR during the 40% MVC increased IFRs, MFRs, and N-EMG_RMS. However, the similar MUAP_AMPS observed between treatments may suggest that a greater load is necessary to recruit additional MUs when performing a single submaximal short-duration muscle action with BFR.