Blood Flow in Humans During Low-Load Exercise with and without Blood Flow Restriction

Blood flow restriction (BFR) in combination with exercise has been well studied, however, little is known about the actual blood flow response to this type of exercise. The range of applied pressures in the research is wide, and previous studies have only examined the blood flow response using the same pressure for every individual independent of limb size, and have only done so at rest, after inflation of the cuff, and following exercise. No investigations have examined this response using relative applied pressures as a percentage of arterial occlusion pressure (AOP) nor have they investigated this within an exercise bout. PURPOSE: To measure blood flow before, during, and after low-load elbow flexion exercise combined with no restriction (NOBFR), 40% of AOP (40BFR), and 80% of AOP (80BFR). METHODS: 140 participants (women=75, men=65) were randomized into one of three conditions. After AOP and one-repetition maximum (1RM) measurement, ultrasound measures of standing blood flow at rest in the right brachial artery were taken. Participants performed four sets comprising 75 total goal repetitions of elbow flexion at 30% 1RM. Blood flow was measured between sets and at one and five minutes post-exercise. RESULTS: Blood flow decreased following inflation, with no difference between BFR conditions (40BFR: 38.1 ml·min−1 vs. 80BFR: 36.3 ml·min−1, p=0.85). Men had greater blood flow than women in all conditions at all time points (411.6 vs. 214.0 ml·min−1, respectively, p<0.001). Maximum blood flow was decreased during exercise with pressure (NOBFR=406.7 ml·min−1, 40BFR=311.1 ml·min−1, 80BFR=188.5 ml·min−1, p<0.001). Blood flow tended to increase across sets regardless of condition. One minute following cuff deflation, blood flow was higher in 80BFR than in 40BFR for women only (372.2 vs. 253.1 ml·min−1, p=0.005). One minute following cuff deflation, there was no group difference in blood flow for men (NOBFR=675.2 ml·min−1, 40BFR=715.4 ml·min−1, 80BFR=666.3 ml·min−1, p=0.75). CONCLUSIONS: The reduction in exercise-induced blood flow during BFR is pressure-dependent, with higher pressures eliciting a decrease in the magnitude of the hyperemic response. Blood flow increased above baseline during all BFR conditions; the use of relative applied pressures ensures that full occlusion does not occur during exercise.