Brachial blood flow under relative levels of blood flow restriction is decreased in a nonlinear fashion

INTRODUCTION: Blood flow restriction (BFR), the application of external pressure to occlude venous return and restrict arterial inflow, has been shown to increase muscular size and strength when combined with low-load resistance exercise. BFR in the research setting uses a wide range of pressures, applying a pressure based upon an individual's systolic pressure or a percentage of occlusion pressure; not a directly determined reduction in blood flow. The relationship between relative pressure and blood flow has not been established. PURPOSE: To measure blood flow in the arm under relative levels of BFR. METHODS: Forty-five people (18-40 years old) participated. Arterial occlusion pressure in the right arm was measured using a 5-cm pneumatic cuff. Blood flow in the brachial artery was measured at rest and at pressures between 10% and 90% of occlusion using ultrasound. RESULTS: Blood flow decreased in a nonlinear, stepped fashion. Blood flow decreased at 10% of occlusion and remained constant until decreasing again at 40%, where it remained until 90% of occlusion. CONCLUSION: The decrease in brachial blood flow is not proportional to the applied relative pressure. The prescription of blood flow restriction should take into account the stimulus provided at each relative level of blood flow.