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Biological Energy Systems

An article by Mike Schultz CSCS of Highland Training

A specific way to design a productive training program is to understand the production and use of energy in biological systems. The recognition of how energy is produced for a specific type of sport or activity provides information needed to target or enhance a specific energy system. Enhancing energy production, that mimics a specific sport or activity, can be done through periodization of a specific training regimen. The main goal of an energy system is to replenish ATP (adenosine triphosphate). The phosphagen, glycolytic, and oxidative energy systems are the energy systems that exist in muscle cells to replenish ATP. All three energy systems are active at a given time; however, the extent to which each is used depends primarily on the intensity of the activity and secondarily on its duration.

The phosphagen energy system provides anaerobic energy for short term, high intensity activities that last from five to ten seconds. Examples of this energy system could range from a power lifter to a ten second sprint at the end of a long distance run. ATP, creatine phosphate, and the enzymes myosin ATPase and creatine kinase provide the chemical reaction to power the phosphagen system. These reactions provide energy at a high rate; however, because ATP and creatine phosphate are stored in the muscle in small amounts, the phosphagen system can not supply energy for continuous long duration activities.

Glycolysis is broken down into two systems called fast glycolysis (anaerobic glycolysis) and slow glycolysis (aerobic glycolysis). Fast glycolysis is the breakdown of carbohydrates (either glycogen stored in the muscle or glucose delivered in the blood) to produce ATP for high intensity muscular activity lasting between six seconds to three minutes. Carbohydrates are the only fuel that can be metabolized for energy (ATP) without the direct involvement of oxygen. Therefore, the importance of carbohydrates in anaerobic metabolism can not be overestimated. Fast glycolysis occurs during periods of reduced oxygen availability in the muscle cell and results in the formation of lactic acid. The ability to clear the acid is the ability to recover. The acid is either oxidized within the muscle or converted to glucose through the Cori cycle. Slow glycolysis takes place when oxygen is present in sufficient quantities. Slow glycloysis takes place in the mitochondria and uses carbohydrates to produce ATP for moderately intense activities lasting between one to three minutes. Slow glycolysis, however, does not produce lactic acid as an end product.

The oxidative system is the primary source of ATP during rest and low intensity activities that last more than three minutes. This system primarily uses carbohydrates and fats as substrates. Protein does not play a significant role except for long-term starvation or long bouts of exercise (>120 min.). At rest approximately 70% of the ATP produced is derived from fats and 30% from carbohydrates. Following the start of an activity, as the intensity increases, there is a shift of substrate preferences from fats to carbohydrates. During high intensity aerobic exercise, almost 100% of energy is derived from carbohydrates if adequate supply is available.

Targeting a specific energy system, within a periodized plan, will enhance that systems ability to produce energy. The intensity and duration of a sport or activity will determine which energy system, and further more, which muscle fiber to target to enhance performance. It is important to remember that all energy systems are active at any given time. The intensity and duration of a sport or activity determines the extent to which each energy system is used. Creating a periodized plan to target specific energy systems is the best way to become stronger and more efficient at any given activity

Mike Schultz CSCS

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