Neuromuscular Adaptations To Low-intensity Blood Flow Restricted Training

Low-intensity blood flow restricted (BFR) training has been shown to induce adaptations in muscular strength and size similar to traditional high-intensity resistance training. However, the reporting of peripheral neuromuscular adaptations is lacking within the current literature. PURPOSE: The purpose of this study was to examine the effects of BFR training on motor unit (MU) firing property relationships. METHODS: 13 untrained males (age: 22 ± 2 yrs; height: 175.7 ± 6.0 cm; weight: 81.9 ± 13.3 kg) were randomly assigned to the BFR (n = 7) or non-BFR (n = 6) group and completed a pretesting visit which consisted of 3 isometric dorsiflexion maximal voluntary contractions (MVC) and subsequent randomized MVC% based ramp contractions at 25%, 50%, 75%, and 100% MVC; a 4-pin surface electromyography (EMG) sensor was placed over the tibialis anterior in order to record muscular activation. Both groups completed 4 weeks (8 sessions) of isokinetic dorsiflexion training at 30% of their daily peak torque values at 60°/s. At least 48 hours after the last training, subjects repeated the pretesting protocol. Surface EMG was decomposed into their constituent motor unit action potential (MUAP) trains, validated, and assessed for relative behavioral properties. The relationship (slopes and intercepts) between MUAP size and mean firing rate (MFR) was calculated. Separate two-way repeated measures ANOVAs (group [BFR v non-BFR] x time [pre v post]) were used to compare slopes and intercepts of MFR vs. MUAP at all intensities. RESULTS: In regard to slopes, there were no significant group x time interactions at any of the intensities (p > 0.05); however, at the 25% slopes, there was a significant main effect for time (p = 0.038). Specifically, the 25% MFR v MUAP slope coefficient increased from pre- to post- (-0.105 ± 0.010 to -0.081 ± 0.005; mean ± SE). In regard to the intercepts, there were no significant group x time interactions or main effects for any of the intensities (p > 0.05). CONCLUSIONS: The main effect for time in the 25% slopes, in addition to a lack of differences in the 25% intercepts, indicates MUAP size increased independently from MFR following BFR training. This shift within the MU pool may be due to the recruitment of MUs at slightly higher thresholds during low intensity contractions, which is common within concurrent literature. President's Excellence in Research Scholars, Tarleton State University