The effects of manipulating human blood flow with exercise

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The use of a tourniquet around a limb during exercise, known as blood flow restriction (BFR) training, has become increasingly popular in both rehabilitative and athletics settings as improvements in strength and muscle mass can occur without the need to lift heavy weights. Emerging evidence further suggests BFR during light intensity aerobic exercise may also improve endurance capacity. In addition to having important utility in the applied setting, BFR offers a unique model to study the response to stressors of the cardiovascular system and downstream organs like skeletal muscle. By carefully emphasizing individual components of the systems that are responsible for cardiovascular regulation, homeostasis, and training adaptation, we can gain insight into the mechanisms that underly the enhanced efficacy of BFR to stimulate change and understand physiological control. Accumulating data suggests that BFR exercise can elicit unexpectedly large increases in fitness, even amongst well trained athletes who are typically resistant to change; yet existing evidence suggests these changes do not appear to be exaggerated at the level of the muscle. As aerobic capacity (VO2max; or the ability to take up and use oxygen) is influenced by both the amount of oxygenated blood supplied and the amount of oxygen extracted from the blood at the working tissue, research is needed to fill the void examining the potential effects of BFR on blood delivery. Oxygenated blood supply to the tissue could be influenced by changes in cardiac function, vascular function, blood volume, blood pressure, blood composition, or some combination of these factors to alter cardiovascular performance. In this research we will specifically seek to understand: 1) the implications of removing (trapping) blood volume from circulation and the short-term effects on volume regulating responses and O2 carrying capacity 2) the effects of blood trapping on the ability of the heart to increase cardiac output, along with the sensitivity of sympathetic nerve activity to control blood pressure and 3) the influence on resting blood pressure and cardiovascular control over time with repeated stressing of these systems. Finally, we will examine the causal role of alterations in plasma volume, O2 carrying capacity, and muscular endurance with alterations in aerobic capacity. We will consider the temporal response of these changes and cause-and-effect relationships with the magnitude of the applied stressor. An understanding of the mechanisms underlying the ability of BFR to elicit adaptations will allow for the optimization of these methods targeted toward causing adaptive changes. As such, this work has implications for use in clinical treatment as well as potential applications to physical performance (national defense, emergency services, athletes), blood services, and astronauts returning from prolonged space travel.