Circulatory effects of isometric muscle contractions, performed separately and in combination with dynamic exercise

Studies on central circulation and regional blood flow were performed in healthy male volunteers at rest, during sustained isometric forearm contraction at 20% of MVC, during dynamic leg exercise (100 W) and during combined isometric and dynamic exercise. In 10 subjects pulmonary oxygen uptake, arterio-venous oxygen difference, heart rate, leg blood flow and blood pressures in the pulmonary and subclavian arteries and in the right atrium were measured. In 4 of these subjects the temperature was measured in mixed venous blood and in subcutaneous tissue in an attempt to further analyse the blood flow distribution through central versus peripheral parts of the circulatory system. In 5 other subjects the splanchnic blood flow was estimated by hepatic vein catheterization and dye dilution technique at rest and during isometric forearm contraction. It was found that cardiac output, oxygen uptake, heart rate and arterial blood pressure all increased in response to isometric contraction. Quantitatively the changes in heart rate and cardiac output induced by a sustained contraction were more marked when the contraction was performed separately than when it was added to dynamic exercise. In spite of the increased arterial pressure, the leg blood flow did not increase significantly. Neither did the splanchnic blood flow increase in response to hand-grip contrmic exercise. Isometric exercise, however, caused a blood temperature fall and a rise in subcutaneous temperature indicating an increased blood flow through the skin. It is concluded that during sustained isometric muscle contraction 1. the blood flow increase is mainly distributed to peripheral circulatory areas, 2. a concomitant dynamic exercixe interferes with the circulatory adaptation only to a small extent.