Energy Used for Physical Activities
The factor that most dramatically increases metabolic rate is strenuous exercise. Short bursts of maximal muscle contraction in a single muscle can liberate as much as 100 times its normal resting amount of heat for a few seconds. For the entire body, maximal muscle exercise can increase the overall heat production of the body for a few seconds to about 50 times normal, or to about 20 times normal for more sustained exercise in a well-trained individual.
Table 72–1 shows the energy expenditure during dif-ferent types of physical activity for a 70-kilogram man. Because of the great variation in the amount of physi-cal activity among individuals, this component of energy expenditure is the most important reason for the dif-ferences in caloric intake required to maintain energy balance. However, in industrialized countries where food supplies are plentiful, such as the United States, caloric intake periodically exceeds energy expenditure, and the excess energy is stored mainly as fat. This under-scores the importance of maintaining a proper level of physical activity to prevent excess fat stores and obesity.
Even in sedentary individuals who perform little or no daily exercise or physical work, significant energy is spent on spontaneous physical activity required to maintain muscle tone and body posture and on other nonexercise activities such as “fidgeting.” Together, these nonexercise activities account for about 7 per cent of a person’s daily energy usage.
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