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 have 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) (300 mm Hg) protocol was compared with a high-force (~80% MVC) free blood flow protocol (HF), until range of motion (0°–90°) was impaired. Torque, velocity, and power
were compared with baseline and between protocols. Maximum voluntary contraction and voluntary activation were assessed during and after each protocol. Muscle twitch, low (20 Hz) and high (50 Hz) tetanus, and compound muscle action potential (Mmax
) area were measured at 0, 2, 5, 10, and 20 min 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 with HF (~23%), with no difference in voluntary activation (~10% loss) between protocols. At FP, velocities for BFO and HF were similarly reduced by approximately 63% and 56%, respectively; however, peak power
decreased more during BFO (~90%) compared with HF (~67%). Total work for BFO was approximately 40% lower than for HF. Peak power
for HF was recovered by 2 min, whereas BFO required 20 min. Low-frequency fatigue
(20 Hz/50 Hz) was greater after BFO (~70% decrease vs ~29% decrease after HF), whereas Mmax
area was unaffected.
Concentric elbow flexions at low-force with BFO cause greater impairments in strength
than HF and, therefore, may be a replacement for high-force exercise used in chronic training.