Neuromuscular Function and Blood Flow Occlusion with Dynamic Arm Flexor Contractions.Med Sci Sports Exerc 2019MS
Blood flow restricted or occlusion exercise enhances muscle hypertrophy and strength during resistance training. The acute effects on voluntary and electrically evoked muscle contractile characteristics with impaired blood flow at low and high contraction forces has not been explored.
On separate days, nine males completed two different protocols of concentric elbow flexor contractions. A repetitive low-force (~25% of isometric maximum voluntary contraction, MVC) with blood flow occlusion (BFO; 300mmHg) protocol was compared to a high-force (~80% MVC) free blood flow protocol (HF), until range of motion (0-90°) was impaired. Torque, velocity and power were compared to baseline and between protocols. MVC and voluntary activation (VA) were assessed during and following each protocol. Muscle twitch, low (20Hz) and high (50 Hz) tetanus, and compound muscle action potential (Mmax) area were measured at 0, 2, 5, 10, and 20min of recovery.
Repetitions to failure (FP) were lower for HF (~16) versus BFO (~21), and MVC at FP was reduced more during BFO (~77%) compared to HF (~23%), with no difference in VA (~10% loss) between protocols. At FP, velocities for BFO and HF were similarly reduced by ~63% and ~56%, respectively, however peak power decreased more during BFO (~90%) compared with HF (~67%). Total work for BFO was ~40% lower than for HF. Peak power for HF was recovered by 2mins, whereas BFO required 20mins. Low-frequency fatigue (20Hz/50Hz) was greater following BFO (~70% decrease versus ~29% decrease following HF), while Mmax area was unaffected.
Concentric elbow flexions at low-force with BFO causes greater impairments in strength and power than HF and therefore may be a replacement for high-force exercise used in chronic training.