You are sprinting as fast as you can for 15 to 30 seconds and then all the sudden fatigue kicks in. You no longer are able to continue at the same intensity. Fatigue occurring in less than 30 seconds of high-intensity exercise is primarily a result of energy system depletion.
ATP-PCr System
The Adenosine triphosphate phosphocreatine, or ATP-PCr, system is the most basic energy system used by the muscles, in which ATP is used to produce energy and PCr is stored energy used to create more ATP. This process is very rapid and can be accomplished without any special structures within the cell and without oxygen. Such anaerobic exercise might include high-intensity activities such as sprinting and powerlifting that last only a few seconds. After the initial three seconds, intensity begins to decline, and fatigue will set in.
Fatigue
During the high-intensity activity, ATP maintains a fairly constant level, but after about three seconds, the PCr level begins to steadily decline because it is used to replenished ATP stores. Exhaustion is reached when both ATP and PCr levels are low and unable to provide the energy for further contractions and relaxations. Since ATP and PCr stores are limited, fatigue is reached between 15 and 30 seconds during an all-out sprint.
Glycoltic System
After the ATP-PCr system begins to decline, glycolysis begins. Glycolysis is the process in which the body converts sugar to glycogen. Glycogen is broken down to produce more PCr, which then produces more ATP. Although, glycolysis does not require oxygen, it does produce pyruvic acid, which requires oxygen to be removed. Pyruvic acid is converted to lactic acid, and too much lactic acid buildup in the muscles can result in muscular fatigue.
Lactate Threshold
Lactate threshold is the point during high-intensity exercise at which blood lactate levels are so high you are unable to keep up with lactate production. Increasing your lactate threshold is one way to help reduce fatigue during short-term exercise. This can be done by increasing the volume of your training, performing regular steady-state aerobic exercise between 50 and 60 percent of your maximum heart rate and incorporating high-intensity interval training into your workout regimen.
References
- "Physiology of Sport and Exercise"; Jack H. Wilmore and David L. Costill; 2004
- University of New Mexico; Lactate Threshold Training; Len Kravitz, Ph.D. and Lance Dalleck, Ph.D.
