How Do BFR Bands Work? Blood Flow Restriction (BFR) Bands restrict or reduce the blood flow to the muscles of the arms or legs during exercise. Since the muscles are receiving less blood flow there is an increase in blood lactate concentration, which leads to swelling. And the result is the production of human growth hormone. Natural human growth hormone results in more muscle mass, reduction in body fat, and overall improvement in health. Additional benefits are that the normal workout requires only half the time because the muscles fatigue more quickly. And all of these results can be accomplished with lighter or no weights. BFR Bands are now part of the training and equipment makeup of professional sports teams and some of the US Olympic teams. And BFR bands are increasingly being used by Physical Therapists to treat their patients' injuries.