High Pressure Blood Flow Restriction Is Necessary For Peripheral Vascular Adaptations With Very Low Loads

Abstract

Low-load resistance exercise combined with blood flow restriction (BFR) has the ability to increase muscle mass following periods of training. Peripheral vascular adaptations to this type of exercise have been examined at loads commonly used [30% of one-repetition maximum (1RM)]. Vascular adaptations occur through flow-induced sheer stress, mechanical compression due to muscular contraction, and circumferential strain induced by pressure waves. Loads lower than 30% 1RM (i.e. 15% 1RM) may not induce enough mechanical stress to stimulate adaptation, and higher BFR pressures may be required. PURPOSE: To examine the peripheral vascular response to eight weeks of training using very low loads combined with differing BFR pressures in the upper body. METHODS: Forearm blood flow (FBF), vascular conductance (FVC), and venous compliance (FCV) were measured using strain-gauge plethysmography before and following eight weeks of 2x/week resistance training of the elbow flexors using 15% 1RM combined with either no BFR [15/0], 40% of arterial occlusion pressure (AOP) [15/40], or 80% of AOP [15/80], and were compared to high load resistance exercise at 70% 1RM [70/0] in 20 men and 20 women. Results reported as Mean (SE). RESULTS: FBF exhibited a condition x time interaction (P=.043). The training response to 15/80 and 70/0 were greater (+0.520 (0.22), +0.616 (0.22) ml·min-1·100ml-1, respectively) than 15/0 and 15/40 (+0.077 (0.22), -0.137 (0.21) ml·min-1·100ml-1, respectively). A similar interaction existed for FVC (P=.032), with 15/80 and 70/0 showing a greater response (+8.286 (2.66), +8.595 (2.6) ml·mmHg-1, respectively) than did 15/0 and 15/40 (+1.813 (2.66), -0.413 (2.6) ml·mmHg-1, respectively). FCV displayed only a main effect of time (P=.044), increasing 0.003 (0.002) %·mmHg-1. CONCLUSIONS: At very low loads (15% 1RM), FBF and FVC were increased only in the high pressure group in a manner not different from high load, lending support to the conclusion that circumferential strain on arterioles can lead to vascular adaptation. The lack of difference in the FCV response implies that even very low loads affect compliance. Future research should examine the possibility of capillarization occurring following repeated exposure to high pressure BFR.