Following change is noted during exercise:

Circulatory changes increase muscle blood flow while maintaining adequate circulation in the rest of the body. The increase in blood flow is instantaneous (and not half a minute later). Blood flow to brain remains unchanged during exercise. Exercise causes increased blood flow to the exercising muscle with reduction of flow to liver, kidney, GI tract and inactive muscles. Blood flow to the brain remains unchanged. The local mechanisms maintaining a high blood flow in exercising muscle include a. fall in tissue P02, a rise in tissue PCO2, and accumulation of K+, and other vasodilator metabolites. The rise in temperature fuher dilates the vessels. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 36. Regulation of Respiration. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.