Effect of skeletal muscle demand on cardiovascular function

Cardiac output is directed primarily to skeletal muscle during exercise. Re cent investigations have examined low different groups of skeletal muscle c ompete for the cardiac output during exercise. To date, there is a lack of consistent findings on a blood flow steal effect of arm versus leg exercise , although the majority of data suggest that leg blood flow is not compromi sed when arm exercise is added to leg exercise. A recent set of experiments have demonstrated that respiratory muscles compete favorably for blood flo w with the legs during maximal exercise. Decreased work of breathing leads to: 1) a decrease in cardiac output, due primarily to reduced stroke volume : and 2) increased leg blood flow and leg vascular conductance. An increase d work of breathing leads to the converse. Exercise performance may also be affected by the work of breathing during heavy exercise due to redistribut ion of blood flow between the chest wall and the locomotor muscles. It appe ars that in contrast to ann exercise, respiratory muscles demand a signific ant portion of the cardiac output during maximal exercise, and the work of breathing normally experienced during heavy exercise compromises leg blood flow.