A researcher is trying to design an experiment to measure the amount of energy a person uses during different activities. He proposes to measure heart rate as an indirect measure of metabolic rate. Which of the following would give him a more precise measure of energy use?

Comparing the amount of sugar released in the urine before and after the activity

Measuring the amount of carbon dioxide released from the lungs during the activity

Monitoring the number of calories voluntarily consumed following the activity

Tracking the increase in sweat production over the course of the activity

The right answer is to measure the amount of released carbon dioxide.

The carbon dioxide exhaled by the lungs can reflect the energy consumed by the body since it comes from the degradation of glucose which is the main energy substrate. And this is a better indicator of energy consumption than measuring heart rate because it can be inflected by several factors.

A is false because glucose is not found in the urine, except in the case of diabetes mellitus.

C is false because the consumption of calories does not mean that we will directly use it.

D is wrong because perspiration is independent of energy consumption, this is a way to cool the body after exercise.

Monitoring the number of calories voluntarily consumed following the activity

Explanation:

A calorie is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius. Calories in present in food serve the purpose of providing energy in the form of heat so that our bodies can function. Our bodies store and "burn" calories as fuel.

During physical activity, more calories are burnt than during voluntary activities. Hence measuring the calories voluntarily consumed is a measure of the energy used during the activity.