Basal metabolic rate (BMR) is the measure of the amount of energy expended per unit of time to maintain a living state at rest. According to Gropper and Smith (2009), it represents the rate at which the body's energy expenditures sustain basic life processes such as heartbeat, blood circulation, respiration, and renal function. Since BMR measurements are often taken when an individual wakes, it also includes the energy the body needs to remain awake. There are many different methods for calculating the BMR, and estimations are often based on body weight, body surface area, and calculation from regression equations that measure an individual's height, weight, age, and gender. Gropper and Smith (2009) state that one estimate of the BMR is based on the body weight raised to the power of 0.75 [54, 57]. Using the equation BMR (kcal/day), weight (W) is measured in Kilograms and raised to the power of 0.75, which is then multiplied by 70 (70*W0.75). The Harris Benedict equation can also be used to determine a person's basal and resting energy needs (Gropper and Smith, 2009). It uses the individual's BMR together with an activity factor to determine daily energy expenditure. To calculate BMR using lean body mass (LBM), the Katch-McArdle Formula is applied, where the BMR is calculated as...

For instance, reduction in BMR and physical activity may lead to weight gain and energy balance, and if this is not accompanied by an age appropriate energy intake; it may lead to dysfunction of the hypothalamus.
The factors that affect BMR include:

Muscle mass: This is the amount of muscle tissue in the body whose functioning depends on high energy levels (Sizer and Whitney, 2008). Therefore, individuals who carry more muscle tissue require more energy.

Body Size: Larger body sizes are often associated with a larger BMR because these bodies tend to have larger fluid volumes and body organs to maintain. According to Sizer and Whitney (2008), the larger the body parts, the more the energy invested in moving them and hence the higher the calories the individual expends.

Age: BMR is often higher in youth because as one gets older, lean body mass declines, which slows the BMR.

Height: Since taller individuals have a larger surface area, Sizer and Whitney (2008) state that their BMR is higher than those of short people.

Environmental factors: Adjusting to heat or cold…