Muscle blood flow during exercise in man

Abstract

The recent development of non-invasive ultrasound for studying blood flow has contributed to knowledge about changes in blood flow to exercising muscle. Using this method, the vessel diameter of conduit arteries, such as the femoral artery and brachial artery, was measured. The diameter of the brachial artery tncreased as handgrip exercise was prolonged, though no changes in diameter were observed in the femoral artery during knee extension exercise. Blood flow to the muscle was impeded mechanically by muscle contraction due to the increased intramuscular pressure even at low intensity (10% MVC). A greater reduction of muscle blood flow was demonstrated during the concentric phase, and it recovered toward the baseline during the eccentric phase. The effect of geometrical changes in muscle fibers on muscle circulation remained to be studied. The Doppler ultrasound method with good time resolution allowed us to investigate the time course of blood flow changes during exercise. The results of previous studies indicated a faster adaptation of muscle blood flow at the onset of exercise, followed by a steady state or gradual increase toward the end of exercise, depending on the exercise intensity. Redistribution of blood flow between active muscles has been an issue of interest; several studies indicated blood flow reduction during combined exercise and others did not. Further studies should be conducted focusing on the combination of the exercise intensity of individual muscle recruited during exercise. Muscle blood flow plays a key role in determining muscle endurance capacity. However, it is still unknown how high muscle blood flow increases during exercise. Accumulation of knowledge about exercise-induced maximal blood flow is needed in relation to training, exercise mode, exercise intensity, exercise frequency and contraction/relaxation schedule during the duty cycle.