Glycogen Depletion and Metabolism of Fatigue

Glycogen is essential to performance for both anaerobic and aerobic activities. Muscles being strenuously exercised will rely on glycogen to power these strength-generating muscle contractions. In endurance exercise, while the primary fuel is fatty acids, glycogen is also utilized. In fact, fat catab olism works better when carbohydrates are being metabolized. Studies on long-term exercise and work performance all indicate the onset of fatigue when glycogen is depleted. This again underscores the importance of adequate carbohydrate intake and glycogen replenishment. Glycogen depletion is just one factor that contributes to the onset of fatigue. The following lists several other fatigue causing factors that athlete is faced with:

• ATP and CP depletion

• Lactic acid accumulation

• Calcium ion build-up in muscles

• Oxygen depletion

• Blood pH decrease

Monitoring Your Metabolism

Until recently, there were no affordable and easy-to-use home testing methods that were designed for athletes to measure key metabolic parameters. Early in 1990, inventor Robert Fritz developed the first useful metabolic testing tool for athletes, NitroStix™. After rigorous testing, and confirmation by the eminent sports physiologist Dr. Thomas D. Fahey, author of the ISSA’s new Youth Fitness Trainer Program and the ISSA’s new Specialist in Strength and Conditioning, this home testing device was made available to the general public. The NitroStix™ made it possible for athletes to monitor their nitrogen balance on a daily basis. The significance of this product cannot be overstated. By measuring your state of nitrogen metabolism you can determine if your protein intake is sufficient and also if certain supplements are being ingested in sufficient amounts to improve nitrogen balance. On the horizon is the newly developed testing device that combines nitrogen balance testing with fat metabolism status. These home tests measure the output of metabolic waste products in urine. They are very easy to use and offer a means to really fine tune your training and nutrition program.

Also developed by B. Fritz and Dr. Fahey is a testing method that was probably the Russian athletes’ best kept secret. This new test provides an economical way to determine testosterone and cortisol levels in the body by analysis of saliva. When the body is overtrained, cortisol levels are increased. Cortisol is a catabolic hormone that stimulates the breakdown of muscle tissue. High amounts in the blood ultimately lead to tissue wasting and negative nitrogen balance. So when the testosterone/cortisol ratio is high, anabolism is prevailing. However, when cortisol levels are high and the ratio is lowered, this is an indication of overtraining. By testing your testosterone/cortisol ratio, you can determine if you are in a state of over training or not. In this way, you can determine how hard you should train, if you should take a few days off, or if training intensity should increase.

In addition handheld portable indirect calorimeters that measures oxygen consumption (VO2) and determine resting metabolic rate (RMR) are being used in the medical field as well as many fitness facilities today. The rate of oxidation or the burning of the calories is different for fats, carbohydrates and protein as discussed earlier in the unit. The food you eat can either be burned to liberate energy, converted into body weight, or it can be excreted. If you light a candle and then place a dome over the candle cutting off the fires source of oxygen, the fire will go out. In the same way our body’s ability to undergo oxidation is contingent on oxygen. If we are getting more oxygen then we should be burning more calories. All foods release heat when they are burned. This release of heat is measured in kilocalories. A calorie is a unit of heat. Practically speaking this unit is too small to be useful, therefore the kilocalorie is the preferred unit in metabolite studies. Not all foods are burned completely to produce energy. Some of them are only partially degraded to provide building blocks to support repair and growth. Generally speaking, the calories coming from protein are used for maintenance, repair, and growth of new tissues and organs. Calories from carbohydrates are used for energy. Calories from conventional sources of a fat are prone to be stored as fat since it already has the same molecular structure as body fat. The heat liberated from a particular food is thus a measure not only of its energy content but also of its tendency to be burned as heat. This is known as the thermogenic effect. Nutrition monitoring plays a vital role in the care of patients with diabetes, heart disease, high blood pressure, and obesity, as well as conditions that place patients at risk for malnutrition, such as cancer, burns, trauma, infection, obstructive lung disease, and HIV. Indirect calorimeters can be used in acute care, long-term care, home care, and clinic-based care settings such as physician offices, rehabilitation centers, and ambulatory surgery centers and fitness based facilities.