Physical exercise increases oxygen consumption and clearance of CO2 as the body attempts to mobilize sufficient resources to support increased energy metabolism. At the start of exercise, demand for ATP increases in order to power muscle contraction, resulting in greater oxygen consumption by tissues and thus lower O2 and higher CO2 levels in the bloodstream. Additionally, due to energy inefficiencies, heat is released as muscles contract.
In order to compensate for these physiological changes, the body has many homeostatic mechanisms to regulate cardiovascular and respiratory systems to restore normal CO2 and O2 levels and maintain safe body temperatures. Notably, the medulla in the brain acts a key regulatory control center that receives action potential inputs from stretch receptors, baroreceptors, and chemoreceptors that detect changes in muscle activity, blood pressure, and pCO2 and stimulates other parts of the body to make adjustments to restore homeostasis.
For instance, stretch receptors detecting increases in muscle activity and chemoreceptors detecting rising PCO2 levels trigger the respiratory center of the medulla to increase respiratory rates to clear more CO2 and obtain more O2. Meanwhile, as heart rate and blood pressure increase cardiac output for oxygenated blood flow, sympathetic signals from the vasomotor center of the medulla decreases to compensate, resulting in vasodilation and bringing blood closer to the skin, allowing extra heat produced by muscles to be released and maintaining a normal body temperature.