Basal metabolic rate and physical activity level

Overview

What affects basal metabolic rate, physical activity level, NEAT, the thermic effect of food, and estimating total energy expenditure.

What you need to know

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Questions from this subtopic

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1. 1

   Define basal metabolic rate.

   Model answer

   Basal metabolic rate (BMR) is the energy used to keep the body alive at complete rest. BMR is measured lying down, awake, in a warm room and about 12 hours after eating.

2. 2

   Which part of daily energy expenditure is usually the largest for an adult?

   Model answer

   BMR is usually the largest part of daily energy expenditure for most adults, well over half of the total. Physical activity and the thermic effect of food make up the rest.

3. 3

   Two women each weigh 70 kg. One is a trained athlete and the other is sedentary. Explain why their energy needs differ.

   Model answer

   The athlete has more muscle, which is more metabolically active than fat, so her BMR is higher. The athlete also has a far higher PAL from training, so her total needs are much greater.

4. 4

   Why do men usually have a higher BMR than women of the same weight?

   Model answer

   Men usually carry more muscle and less body fat than women of the same weight. Muscle uses more energy at rest, so men's BMR is higher.

5. 5

   How and why does BMR change with age in adults?

   Model answer

   BMR falls gradually through adulthood as muscle mass declines. Older adults are also often less active, which speeds the loss of muscle.

6. 6

   Which hormones affect BMR, and how?

   Model answer

   Thyroxine from the thyroid gland sets the rate of metabolism, so an overactive thyroid raises BMR. Adrenaline raises metabolic rate in response to stress or cold.

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