The direct effects of physical activity interventions on energy expenditure are relatively small when placed in the context of total daily energy demands. Hence, the suggestion has been made that exercise produces energetic benefits in other components of the daily energy budget, thus generating a net effect on energy balance much greater than the direct energy cost of the exercise alone. Resting metabolic rate (RMR) is the largest component of the daily energy budget in most human societies and, therefore, any increases in RMR in response to exercise interventions are potentially of great importance. Animal studies have generally shown that single exercise events and longer-term training produce increases in RMR. This effect is observed in longer-term interventions despite parallel decreases in body mass and fat mass. Flight is an exception, as both single flights and long-term flight training induce reductions in RMR. Studies in animals that measure the effect of voluntary exercise regimens on RMR are less commonly performed and do not show the same response as that to forced exercise. In particular, they indicate that exercise does not induce elevations in RMR. Many studies of human subjects indicate a short-term elevation in RMR in response to single exercise events (generally termed the excess post-exercise O2 consumption; EPOC). This EPOC appears to have two phases, one lasting < 2 h and a smaller much more prolonged effect lasting up to 48 h. Many studies have shown that long-term training increases RMR, but many other studies have failed to find such effects. Data concerning long-term effects of training are potentially confounded by some studies not leaving sufficient time after the last exercise bout for the termination of the long-term EPOC. Long-term effects of training include increases in RMR due to increases in lean muscle mass. Extreme interventions, however, may induce reductions in RMR, in spite of the increased lean tissue mass, similar to the changes observed in animals in response to flight.

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Physical activity and resting metabolic rate

Hyperactivity in patients with anorexia nervosa and in semistarved rats: evidence for a pivotal role of hypoleptinemia.

The thermogenic responses of ten lean and ten moderately obese women to food, exercise, and food plus exercise were measured using open circuit respirometry for five minutes every half hour for four hours under six conditions: during five minutes of bicycle exercise at a workload of 300 kpm/min with and without eating a 910 kcal mixed meal; cycling at a workload just below the anaerobic threshold with and without food; and at rest with and without food. Over the four-hour period, the thermic effect of food at rest was similar for the lean and obese groups: 50 kcal and 47 kcal, respectively. Eating before exercise increased the exercise metabolic rate by 11% for the lean women and by 4% for the obese women (P less than 0.005). Exercise potentiated the thermic effect of food for the lean women but nor for the obese women: the thermic effect of food was 2.54 times greater during exercise than at rest for the lean group, but only 1.01 times greater for the obese women (P less than 0.005). This reduced response to the combined stimulus of food plus exercise may constitute a subtle metabolic factor associated with obesity.

Thermic effects of food and exercise in lean and obese women

Gender and energy balance: Sex differences in adaptations for feast and famine

The relationship between size of a mixed, liquid meal and the thermic effect of food (TEF) was studied in two groups of nonobese male subjects differing in maximum aerobic capacity (VO2 max) A design using repeated measures was chosen in which each subject received each meal (water, 500 kcal, 1000 kcal, 1500 kcal) on a different morning TEF was measured by indirect calorimetry for three hours following each meal and was found to increase systematically, in a nonlinear fashion, as meal size was increased Subjects with a high VO2 max responded to the two higher calorie meals with a greater TEF than did subjects with a low VO2 max They also showed a greater increase in TEF for any given increase in meal size This study establishes a precise relationship between meal size and the thermic effect of food It also identifies an important variable, VO2 max, in determination of the individual thermic response to food These findings suggest that individuals with a high VO2 max (such as aerobically trained athletes) show a greater caloric expenditure after eating, particularly after a large meal, than do individuals with a low VO2 max A high thermic response to food could be beneficial in body weight homeostasis

Meal size and thermic response to food in male subjects as a function of maximum aerobic capacity

1. The energy metabolism of ad lib .-fed adult male Wistar rats receiving daily running exercise (0·9 km/d; 8° incline) on a motor-driven treadmill, over a period of 56 d, was compared with that of sedentary ad lib .-fed rats and sedentary restricted-fed rats of similar body-weight (approximately 420 g). 2. The metabolizable energy of the diet (Oxoid 41B) was 11·44 ± 0·05 kJ/g. This value was not affected by restricted feeding (70% ad lib .), exercise training or exercise itself. 3. Exercise-trained rats ate 5% more food than the sedentary ad lib .-fed rats but their equilibrium body-weight was 60 g lower than that of the latter group. 4. Resting metabolic rate, measured over 22 h in a respiration chamber was increased by 10% in exercise-trained animals. 5. Feeding increased energy expenditure (dietary-induced thermogenesis) and this effect was potentiated by performance of an exercise task. 6. Exercise-trained rats exhibited anticipatory rises in energy expenditure (approximately 40%) when placed on a stationary treadmill. 7. Treadmill work increased energy expenditure by a factor of 1·9–2·4. 8. The energy cost of the exercise, determined by respiration calorimetry was 66–80 J/g per km. These energy costs did not account for all the differences observed in food energy consumption of exercise-trained and sedentary rats of equal body-weight. 9. It is concluded that regular physical exercise increases energy expenditure by factors additional to the energy requirement directly related to the physical work. These factors include an increased resting metabolic rale in exercise-trained rats, increased dietary thermogenesis induced by exercise and anticipatory increases in energy metabolism during the period preceding exercise.

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Waring Jj

Papers

The effects of physical exercise on metabolic rate and dietary-induced thermogenesis.

The effects of exercise and exercise training on dietary induced thermogenesis.

Thermogenic effects of diet and exercise.