Editing Exercise physiology (section)

=== Oxygen ===

Vigorous physical activity (such as exercise or hard labor) increases the body's demand for oxygen. The first-line physiologic response to this demand is an increase in [[heart rate]], [[breathing rate]], and [[deep breathing|depth of breathing]].{{cn|date=April 2025}}

Oxygen consumption (VO<sub>2</sub>) during exercise is best described by the [[Fick Equation]]: VO<sub>2</sub>=Q x (a-vO<sub>2</sub>diff), which states that the amount of oxygen consumed is equal to [[cardiac output]] (Q) multiplied by the difference between arterial and venous oxygen concentrations. More simply put, oxygen consumption is dictated by the quantity of blood distributed by the heart as well as the working muscle's ability to take up the oxygen within that blood; however, this is a bit of an oversimplification. Although cardiac output is thought to be the limiting factor of this relationship in healthy individuals, it is not the only determinant of VO2 max. That is, factors such as the ability of the lung to oxygenate the blood must also be considered. Various pathologies and anomalies cause conditions such as diffusion limitation, ventilation/perfusion mismatch, and pulmonary shunts that can limit oxygenation of the blood and therefore oxygen distribution. In addition, the oxygen carrying capacity of the blood is also an important determinant of the equation. Oxygen carrying capacity is often the target of exercise ([[ergogenic aids]]) aids used in endurance sports to increase the volume percentage of red blood cells ([[hematocrit]]), such as through [[blood doping]] or the use of [[erythropoietin]] (EPO). Furthermore, peripheral oxygen uptake is reliant on a rerouting of blood flow from relatively inactive [[viscera]] to the working skeletal muscles, and within the skeletal muscle, capillary to muscle fiber ratio influences oxygen extraction.{{cn|date=April 2025}}