Aerobic Versus Anaerobic

My chosen athlete is a triathlete during the running phase of the triathlon.

As your athlete performs the chosen activity, discuss whether rapid or slow glycolysis is the most effective means of energy transfer?

Rapid anaerobic glycolysis reactions only release roughly 5% of the potential energy present in a glucose molecule. It is the main energy source when rapid type II muscle fibers are being used. In order for the body to sustain an exercise for more than a couple of minutes, it must tap into another fuel source. A triathlon includes a swim portion of 0.93 miles, a cycling portion of 24.8 miles and run of 6.2 miles. Slow aerobic glycolysis is the most effective mean of energy transfer during a triathlon run of 6.2 miles, which utilizes type I muscle fibers. The body must sustain exercise for an average of 1 hour or more, depending on the athlete’s fitness level (Sahlin, 1990).

What physiological factors contributed to your analysis (e.g. hydrogen release, lactate formation, glucose catabolism, etc.)? How did these factors influence your choice?

The physiological factor that contributed to my analysis was glucose catabolism. Glycogen is the main source of energy use to resynthesize ATP in both aerobic and anaerobic systems. The human body cannot work anaerobically for more than a couple of minutes, eventually it will breakdown without the presence of oxygen. Since the triathlete is working well beyond that 2-minute threshold, the athlete must derive energy aerobically. The aerobic system breakdowns glycogen in the presence of oxygen, producing little to no lactic acid. Therefore, the athlete can continue to exercise for a substantial amount of time. In times of prolonged work, 2-3 hours, fats and proteins may be broken down to replenish ATP storage as glycogen is depleted. The by-products of carbon dioxide and water are eliminating through perspiration and respiration. The rate at which the ATP is replenished is dependent on the aerobic capacity of the athlete. The more efficiently the athlete can consume oxygen, the more efficiently the body can produce the ATP required to sustain physical activity (Berg, 1970).

Explain the benefits of lactate for optimal performance of the chosen activity.

Since a triathlon is an endurance event, the body is mainly using type I muscle fibers. Lactate can be utilized by the type I muscle fibers as an energy source. Lactate can provide more energy required for repetitive muscle contractions. Lactate can also be used as fuel for the brain and heart and can be converted to glucose in the liver. The use of lactate as fuel within the muscle itself depends on how well a person’s endurance muscle fibers are trained aerobically. In other words, the ability for a triathlete to derive energy from lactate is based on their training for the event. If they trained properly for the event, it could be assumed that the body will more easily derive oxygen from lactate.


Berg, J. M. (1970, January 01). Fuel Choice During Exercise Is Determined by Intensity and Duration of Activity. Retrieved from

McArdle, W. D., Katch, F. I., & Katch, V. L. (2016). Essentials of exercise physiology. Philadelphia: Wolters Kluwer.

Sahlin, K. (1990, June). Muscle glucose metabolism during exercise. Retrieved from