This is brought about by a large increase in blood flow to active muscle, which is met by increasing the cardiac output and vasodilatation of muscle blood vessels. Exercise is a clear reminder of the close co-operation between the respiratory and cardiovascular systems . Dynamic - e.g. walking, running, cycling. Contraction intermittent, and although muscle blood flow may be impeded during contraction there is sufficient relaxation time for adequate overall flow. Isometric e.g. tooth clench and load holding.
Intramuscular pressure reduces blood flow and muscle becomes oxygen depleted.
Responses to both types are different. At start of exercise muscle oxygen use immediately rises. Lung oxygen uptake lags but reaches steady state within 2 min. Fig A Oxygen consumption is proportional to work rate initially but then levels off. Further work relies on anaerobic mechanism.