The aerobic threshold is the exercise intensity at which the body starts to rely more on carbohydrates for energy instead of fats. This point is significant because it marks the transition from predominantly aerobic metabolism, where oxygen is used efficiently, to a more anaerobic state, where lactic acid begins to accumulate. Training at or just below the aerobic threshold can improve endurance and overall fitness. Athletes often use this threshold to optimize their training, ensuring they build stamina without excessive fatigue. Monitoring heart rate can help determine an individual's aerobic threshold during workouts.