Metabolism of Exercise
Energy Expenditure
The average daily energy expenditure of males is between 2700 and 3000 kcal per day, whereas the average daily energy expenditure of females is between 1800 and 2100 kcal per day. Great variability in energy expenditure exists, however, because of varying physical activity levels from day to day and between individuals.
Because oxygen is used to convert food energy to muscle energy, energy expenditure during exercise is typically calculated from oxygen consumption. Walking is the most common form of exercise, and the relationship between walking speed and oxygen consumption is essentially linear between speeds of 3.0 and 5.0 km per hour. For example, the range of energy expenditure between speeds of 3.0 and 5.0 km per hour is between 2.5 and 4.5 kcal per minute. At faster speeds, walking becomes less efficient and at speeds greater than 8 km per hour, jogging or running becomes more efficient. Other factors which influence energy expenditure during walking include body weight, walking surface, and footwear. During running, the total caloric cost for a given distance is about the same irregardless of speed (1kcal-kg-1-km-1). Children are less economical runners than adults requiring 20-30% more oxygen per unit body weight. Conversly, trained athletes are more efficient runners than non-trained individuals. Thus, at a given speed, trained athletes can perform at lower aerobic capacities and can conserve carbohydrate stores. Or alternatively, trained athletes can increase their running speed to match the oxygen consumption of a less trained individual.
Resting Metabolic Rate & Exercise
Resting metabolic rate (RMR) increases following acute bouts of exercise. The degree and duration of this exercise induced RMR increase, however, remains uncertain. Factors which confound accurate determinations of RMR increases include exercise intensity, duration, and frequency parameters, dietary composition and regulation, and subject body weight, body composition, and age factors. To date, it appears relatively small differences in total RMR are involved, and further research is required to put these differences in perspective.
References
McArdle, W. D., F. I. Katch, and V. L. Katch. Exercise Physiology: Energy, Nutrition, and Human Performance. Phila., PA: Lea & Febiger, 1986.
Sims, E. A., Exercise and energy balance in the control of obesity and hypertension. Exercise, Nutrition, and Energy Metabolism, ed. Horten, E. S. and Terjung, R. L., New York, NY, Macmillan Publishing Company, 1988.
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