REQUIREMENTS FOR MODERATE EXERCISE
FLUIDS AND OXYGEN
Fluids: More water is needed with increase in exercise. The need to replace fluid losses during exercise is well recorded. All cellular activities take place in an aqueous medium. Water carries nutrients and waste products via blood steam to and from the cells. Thus sufficient blood volume is a must to ensure loss of heat produced through skin and water. Water is lost from the body through sweat and respiration. Water for sweat is taken from blood, resulting in reduced blood volume, which may endanger heart function. Significant fluid losses may reduce sweating and blood flow, disturbing body temperature regulation. A water loss of 4 to 5 per cent reduces work capacity by 20 to 30 per cent; a 10 per cent loss may result in circulatory collapse.
The fluid losses in exercise depend on the duration and intensity of exercise as also the ambient temperature and humidity. Normal sweat production, without exercise, is 500 to 700 ml per day. It may increase to 8 to 12 liters per day with prolonged exercise in humid conditions.
Electrolytes: Though sweat contains electrolytes, chloride, magnesium and potassium, performance is not distributed by electrolyte losses. In hot months, during training, a dilute salt solution (1/2 teaspoon salt p0er liter) may be used as a rehydration drink to correct exercise sweat losses.(American College of Sports Medicine, 1984.).
During exercise, as heat is released with energy production, the body temperature due to sweat must be made up to avoid dehydration. The amount of water needed in hot summer months is much more than in cool weather.
Oxygen: Breathing ensures a constant supply of oxygen to the body. The need for oxygen increases with exercise, as more oxygen is needed to release extra body energy. The ability of the body to provide the oxygen needed is known as aerobic capacity. The aerobic capacity is dependent on the fitness of tissues involved in oxygen intake and transport --- lungs, heart and blood vessels and the body composition.
Body Fitness: Body fitness is measured in terms of aerobic capacity. Aerobic capacity is the ability of the body to provide the increased demands for oxygen and use it during exercise. As it varies with the body size, it is measured as the amount of oxygen consumed per kilogram body weight. Thus it is an indirect measure of the health of the respiratory system.
Body Composition: As mentioned in the energy balance chapter, the muscle mass (lean body mass or the active metabolic tissues) in the body uses larger part of the oxygen. The aerobic capacity is dependent on the percentage of lean body mass and body fat. Body composition is determined by these two components of body weight.
Nutritional Needs for exercise: Any exercise activity increases energy expenditure. Proper diet is an essential prerequisite for good performance be it for athletic competition or for just keeping fit. It is important to have nutrient reserves to meet the demands during periods of exercise. If the reserves are used up, the body cannot meet its needs and fatigue and exhaustion may occur. As we know, carbohydrates and fats are the basic suppliers of those energy reserves, as very little is drawn from protein.