Which energy system takes over during prolonged exercise?

The energy system that takes over during prolonged exercise is aerobic respiration. This system is the most efficient for sustaining long-duration activities because it utilizes oxygen to convert carbohydrates, fats, and sometimes proteins into adenosine triphosphate (ATP), the energy currency of the body.

Aerobic respiration is essential for activities that last longer than several minutes, such as distance running or cycling, as it can produce a large amount of ATP over an extended period. Since this system relies on oxygen, it allows the body to continue producing energy as long as aerobic conditions can be maintained and fuel sources are available.

In contrast, the phosphagen system and glycogen-lactic acid system are better suited for short bursts of high-intensity efforts. The phosphagen system provides immediate energy for activities lasting only a few seconds, while the glycogen-lactic acid system kicks in for moderately-intense exercise lasting around 30 seconds to 2 minutes, leading to the accumulation of lactic acid that can limit performance over time. Glycolysis also typically refers to the breakdown of glucose for energy, which can support exercise but becomes less efficient than aerobic metabolism during prolonged workloads. Therefore, for sustained activities requiring stamina and endurance, aerobic respiration is the primary source of energy.