What type of metabolism occurs when a horse breaks into a run from a standstill?

When a horse breaks into a run from a standstill, it's primarily utilizing anaerobic alactic metabolism. This type of metabolism allows for immediate energy release without the need for oxygen and without producing lactic acid.

Anaerobic alactic metabolism relies on stored adenosine triphosphate (ATP) and phosphocreatine (PCr) in the muscles. These energy sources are quickly accessible, providing the horse with the ability to sprint rapidly over short distances. During this immediate phase of high-intensity exercise, the horse can generate a significant burst of speed without fatigue from lactic acid buildup, which would occur in longer-duration efforts.

In contrast, anaerobic lactic metabolism kicks in after the initial burst when the horse needs sustained effort, leading to lactic acid production. Aerobic metabolism, which uses oxygen to generate energy, is more suited for longer, moderate activities rather than quick sprints. Lastly, aerobic lactic is not a recognized metabolic pathway; rather, aerobic and lactic metabolism are distinct processes that are not typically combined in this manner. Therefore, understanding these energy systems is crucial for recognizing how horses perform during different intensities of exercise.