The number of calories that the body burns during regular daily activities or exercise is dependent on various factors, so it is not an exact science. The results of this calculator (and any other) are based on standardized data that references an "average" person, so it is only an estimate. The calculator uses MET (Metabolic Equivalent of Task) values to determine exercise intensity.

Factors Affecting Calories Burned

The calculator uses three key factors: body mass, duration of activity, and MET (metabolic equivalent of task). However, other factors also influence calories burned:

• Body Mass: A person who is larger due to more muscle, fat, or height burns more calories. A 200-pound person burns significantly more calories running 1 mile than a 100-pound person.
• Duration: The longer a person performs an exercise, the more calories they will burn. However, intensity also matters - walking 1 mile in 1 hour burns fewer calories than running 5 miles in that hour.
• Exercise Intensity: Measured by MET values. Higher intensity exercises have higher MET values and burn more calories per minute.
• Age: As a person ages, they tend to lose lean body mass, which decreases metabolic activity. Older people burn fewer calories overall.
• Body Composition: Muscle requires more energy than fat. A person with more muscle will burn more calories performing the same activity.
• Temperature: People burn more calories in warmer environments because higher temperature increases body temperature.
• Fitness Level: A person in better shape burns fewer calories performing the same exercise because their body is more efficient.
• Diet and Sleep: These affect metabolism, which influences the total number of calories burned.

Understanding MET Values

MET (Metabolic Equivalent of Task) is the ratio of the rate at which a person expends energy while performing a given physical task compared to a reference (sitting quietly). By convention, the reference is based on the energy expended by an "average" person while sitting quietly, which is roughly equivalent to 3.5 mL of oxygen per kilogram per minute.

A MET value of 1 represents the energy expended at rest. An activity with a MET value of 2 requires twice as much energy, a MET value of 8 requires eight times as much energy, and so on. Exercises are commonly categorized as light intensity (lower MET), moderate intensity (medium MET), or vigorous intensity (higher MET).

Exercise Intensity and Fat Burning

Exercise intensity affects the type of fuel (carbohydrates, fats, protein) that the body uses. Generally, lower intensity exercises burn more fat as a percentage of total calories, so if a person's goal is to burn fat, they should perform low intensity exercises for longer durations. As exercise intensity increases, the body shifts from using fats to using carbohydrates instead.

Accuracy of the Calculation

The accuracy of this calculation is significantly affected by MET values. By convention, 1 MET is roughly equivalent to expending 1 Calorie per kilogram of body weight per hour. This convention was derived based on a single specific subject: a healthy 40-year-old male who weighed 70 kilograms. A person's resting metabolic rate (RMR) is highly dependent on factors such as lean body mass, age, health status, and more.

The estimate is also affected by the fact that MET values were derived under the assumption that the activity is performed at a constant rate. For example, playing tennis for 1 hour can involve taking breaks between games, resting, chatting, etc., meaning that the activity is only truly performed for a shorter duration. This can result in an overestimate of calories burned.

Sources & References