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About energy expenditure - at rest and during exercise

The amount of energy the body consumes at rest and throughout the day is of interest for those wishing to lose weight, or those wishing to control their diet to match their energy output. The components that make up your body's total energy expenditure are the energy you use at rest (which makes up most of the energy), diet-induced thermogenesis and the additional energy that is expended during physical activity (METs). Many factors affect these values, and equally, there are many ways to get a measure of these values.

Measurement Methods

You can get a good measure of the body's energy expenditure by directly measuring your oxygen consumption (VO2) or by direct calorimetry. Either method is not easily done, particularly when taking measurements during physical activity and throughout the day. Instead, there are several simpler methods for estimating energy expenditure, though these are not always as accurate, as there are many factors affecting the actual energy expenditure, such as activity level, age, gender, size, weight and body composition. The most simple method is to use a formula for calculating energy expenditure. Other methods include heart-rate monitoring, surveys and motion sensors. You can also use a pedometer or smart watch to estimate your daily energy expenditure.

Energy Expenditure at Rest

Resting Metabolic Rate (RMR) and Basal Metabolic Rate (BMR) are both measures of resting energy expenditure, representing the minimum amount of energy required to sustain the body's vital functions, including the heart, lungs and temperature regulation.

The most common method for measuring basal metabolic rate is to determine the body's oxygen consumption at rest. A less common method is to use direct calorimetry which measures the heat generated by the body in an enclosed space. If you are unable to access the equipment for directly measuring BMR, a value can be estimated using calculations based on your weight, height and age. See more about BMR.

man lying down on the grassEven at rest your body is working

If you wish to lose weight, generally you need to have a higher energy expenditure than the amount of energy you take in (through food). Most diets involve reducing your intake, but you can also lose weight by increasing your energy expenditure. You could just do more exercise, which is the usual advice, alternatively you could also boost your resting metabolism. If you can increase your basal metabolic energy consumption (or metabolism), you will increase your energy consumption - 24 hours a day. One way to do this is to increase the amount of muscle mass in your body with resistance exercises. Check out these articles on this topic:

Energy Expenditure during Exercise

Physical activity has a large effect on total human energy expenditure, and contributes 20-30% to the body's total energy output. The amount of energy expended for different activities will vary with the intensity and type of exercise. For runners, we have a simple calculator to determine the number of Calories Burned Running. There are also tables for working out Power while Running, or you can use a pedometer.

Commonly used in exercise science, you can use indirect calorimetry to measure the amount of oxygen that is being consumed by the body to produce energy. The body's oxygen consumption (VO2) can be measured during exercise on many different exercise modes such as treadmill running and cycling.

A less common way to measure energy consumption during exercise is Human Whole Body Direct Calorimetry, which obtains a direct measurement of the energy use of the body by measuring the amount of heat generated by the body.

An easier method of estimating the intensity of physical activity is the Metabolic Equivalent Task (MET) method. The energy cost of many activities has been determined, usually by monitoring the oxygen consumption during the activity, to determine an average oxygen uptake per unit of time. This value is then compared to the resting oxygen uptake. One MET is the energy expended at rest, two METs indicate the energy expended is twice that at rest, three METs is triple the resting energy expenditure, etc.

Daily Energy Expenditure

There are many ways to estimate your total daily energy expenditure, such as simple formula based on body weight, or using activity factors to multiply BMR. The total daily energy expenditure includes your resting energy expenditure, plus the need to adjust for the amount of activity performed throughout the day. For each person, the range for total daily energy expenditure is highly variable, it depends on many factors, including activity level, age, gender, size, weight and body composition.

There are a few formulas for Calculating Daily Energy Expenditure, or you can use this Daily Calorie Counter, an online calculator for determining how many calories you need each day. The result is based on your entered height, weight and your estimated activity level. You can also use a pedometer or smart watch to get a measure of your daily energy expenditure.

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