What initiates energy supply immediately during exercise?

The phosphagen system is responsible for providing immediate energy during short bursts of intense physical activity. It relies primarily on stored adenosine triphosphate (ATP) and creatine phosphate (CP) within the muscles, enabling a quick release of energy for high-intensity exercise lasting up to about 10 seconds. This system does not require oxygen, allowing for rapid energy production to fuel activities such as sprinting, weightlifting, or any other form of exertion that demands a quick, high-energy output.

In contrast, other energy systems like the glycogen-lactic acid system take longer to ramp up and provide energy, as they rely on anaerobic glycolysis and can produce energy for slightly longer durations but not instantaneously. Aerobic respiration and oxidative systems primarily cater to prolonged activities and also depend on a supply of oxygen, making them less effective for burst activities.