Nutrition of Athletes
Effects of Physical Activity
Physical activity will introduce long-term metabolic and physiological effects on the body. These effects as elucidated by Astrand are:
* Increase in maximal oxygen uptake and cardiac output-stroke volume
* Reduced heart rate at given oxygen uptake
* Reduced blood pressure
* Reduced heart rate x blood pressure product
* Improved efficiency of heart muscle
* Improved myocardial vascularization?
* Favorable trend in incidences of cardiac morbidity and mortality
* Increased capillary density in skeletal muscle
* Increased activity of "aerobic" enzymes in skeletal muscles
* Reduced lactate production at given percentage of maximal oxygen uptake
* Enhanced ability to utilize free fatty acid as substrate during exercise-glycogen saving
* Improved endurance during exercise
* Increased metabolism-advantageous from a nutritional standpoint
* Counteracts obesity
* Increase in the High density/low density lipoprotein ratio (HDL/LDL)
* Improved structure and function of ligaments, tendons, and joints
* Increased muscular strength
* Reduced perceived exertion at given work rate
* Increased release of endorphins
* Enhanced tolerance of hot environment-- increased rate of sweating
* Reduced platelet aggregation?
* Counteracts osteoporosis (especially for women)
* Can normalize glucose tolerance
Consequently, accompanying these changes in the body, there is an increased need for energy and nutritional support to sustain the prolonged physical conditioning and training of athletes as well as to maintain normal bodily functions.
References
Astrand, Per-Olof. Long-Term Effects of Participation in Physical Activity. Abstracts: New Horizons of Human Movement. 1988. 63-66.
Energy Needs
The energy needed to maintain the body's needs come from food energy. Energy is measured in kilocalories (kcal), which is a unit of measure that is the amount of heat (4.184 kJ) needed to raise the temperature of 1 kg of water one degree Celsius at standard atmospheric pressure (760 mm Hg). The relationship between energy intake, expenditure and storage is known as the energy balance. When more energy is consumed than is expended, it is then stored by the body as fat. Each individual has a basic daily caloric requirement determined by the basal metabolic rate (BMR), which is the energy needed to maintain bodily functions such as: body temperature, cardiac function, cellular functions, and respiration when the body is at rest and not feeding. The BMR is dependent on body weight and people with higher body weight have a higher BMR.
Physical exercise increases energy expenditure and therefore the caloric intake requirement. The total energy needs of a person depend on a complex interrelationship between body weight, the basal metabolic rate, and activity level.
Physical exercise increases energy needs and therefore the caloric intake requirement also increases. The main concern of athletes is whether there is sufficient caloric intake to meet the increased physical activity involved during conditioning, training or competition. Although the goal is to achieve and maintain an optimal body weight and composition (i.e. % body fat), there are many factors affecting energy expenditure during exercise, such as: age, sex, body weight and size, and the type, intensity, frequency, and duration of the sport activity. There is no precise energy requirement for athletes engaged in specific activities or sports, but the greater the intensity and duration of exercise, the larger the caloric intake, with a minimum of 3000 kcal per day for training. Endurance sports and events have greater energy expenditure than other types of sports. For example, people engaged in cross-country skiing or marathon running may have a caloric intake of 4000-6000 kcal per day. In contrast, people involved in short duration, high intensity exercise (lasting up to a minute) such as sprints and short yardage swimming events (50 and 100 yards) may have a caloric intake of about 3000-4000 kcal a day. To facilitate optimal performance, an athlete's diet must have adequate amounts of nutrients which are categorized as fuel and non-fuel. The fuel nutrients supply the body with energy and these are carbohydrate, fat and protein. The U.S. Recommended Daily Allowance (USRDA) for athletes of carbohydrates, protein and fats are measured in percentage of calories from the diet: 55% carbohydrate, 30% fat, and 15% protein. The non-fuel nutrients are vitamins, minerals, trace elements and water. The non-fuel nutrients are essential because their deficiency in the body results in health problems. Some physicians and nutritionists sometimes use metabolic enhancers (metabolites) which are non-essential non-fuel nutrients.
References
Buskirk, E.R. Some Nutritional Considerations in the Conditioning of Athletes. Ann. Rev. of Nutr. (Darby, Broquist and Olson, Eds.). 1981. 1:319-50.
Buskirk, E.R. Diet and Athletic Performance. Postgrad. Med. 1977. 61:229-36.
Diet and Health: Implications for Reducing Chronic Disease Risk. Committee on Diet and Health Food and Nutrition Board and Commission on Life Sciences and National Research Council. National Academic Press, Washington D.C. 1989. pp. 139-142; 159;259; 273-276; 291-2.
Hollmann, W., H. Liesen, and A. Mader. Metabolic Capacity. The Olympic Book of Sports Medicine. Vol.1. (Dirix, Knuttgen, and Tittel. Eds.) Blackwell Scientific Publications, London. 1988. 58-68.
Energy Metabolism & Utilization
Non-fuel Nutrients
Ergogenic Support of Athletes
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