Homeostasis is the process of regulating the internal environment of an organism. Homeostasis is critical to organisms so that they can survive changing environmental conditions.
The human body is able to regulate things like oxygen level, CO2 level, temperature, pH, and blood sugar in order to maintain a consistent internal environment.
When a person exercises, oxygen is used. In order to maintain homeostasis, the human body increases the rate of breathing to expel CO2 waste and to maintain oxygen levels.