Acute effects of exercise under different levels of blood-flow restriction on muscle activation and fatigue

Abstract

Purpose: There is some evidence that muscular activation during exercise is enhanced by higher levels of blood flow restriction (BFR). However, the impact of different relative levels of BFR on the acute neuromuscular response to resistance exercise is not yet fully understood. We examined the acute effects of low-intensity knee extensions [20 % of 1-repetition maximum (1RM)] with BFR on muscle activation, neuromuscular fatigue and torque in the rectus femoris (RF) and vastus medialis (VM) muscles.

Methods: Fourteen men (24.8 ± 5.4 years) exercised at 20 % 1RM combined with 40, 60 and 80 % BFR. Restrictive pressures were calculated based on direct blood-flow measurements taken at rest on each participant. Torque was determined during pre- and post-exercise maximal voluntary contractions. Surface electromyographic activity [root mean square (RMS)] was obtained during dynamic and sustained isometric contractions before and after exercise. The median frequency (MF) of the electromyographic power spectrum was computed for isometric contractions.

Results: Torque only decreased in the 80 % BFR condition (-5.2 %; p < 0.01). Except for the VM in the 40 % BFR, MF decreased in both muscles post-exercise in all conditions (p < 0.01). MF decrements were of greater magnitude post-exercise at higher levels of BFR. RMS increased within all sets in both muscles (p < 0.01) and attained higher values in the 80 % BFR condition; except for set 1 in the RF muscle (p < 0.01).

Conclusion: Muscular activation, as well as neuromuscular fatigue, varies as a function of relative BFR intensity. Therefore, the individual determination of vascular restriction levels is crucial before engaging in BFR exercise.

Keywords: Electromyography; Muscular activation; Neuromuscular fatigue; Resistance training; Vascular occlusion.