The power metabolic rate is the total energy consumption of a person within 24 hours minus his basal metabolic rate, which corresponds to the maintenance requirement fasting at rest. Power metabolic rate depends mainly on activity and weight and, like basal metabolic rate, is expressed in kilocalories or kilojoules. Since a direct measurement is associated with very high effort for most activities, the power metabolic rate is determined approximately by multiplying the basal metabolic rate by the dimensionless factor PAL (Physical Activity Level).
What is power metabolic rate?
Power metabolic rate corresponds to a person’s total energy expenditure in a 24-hour period beyond that required to maintain basic physical functions (basal metabolic rate). Power metabolic rate corresponds to a person’s total energy expenditure in a 24-hour period beyond maintaining basic bodily functions (basal metabolic rate). Basal metabolic rate is the daily energy consumption of a person at complete rest, fasting, and at an ambient temperature of 28 degrees Celsius, at which the body does not have to expend any additional power to maintain body temperature. Like basal metabolic rate, power metabolic rate is expressed in kilojoules or kilocalories. Direct measurement of the total metabolic rate (basal metabolic rate plus power metabolic rate) encounters technical difficulties in many physical activities and would involve considerable effort. For this reason, one usually makes do with an approximate calculation of the total metabolic rate using the PAL factor (Physical Activity Level), by which the basal metabolic rate is multiplied. For physically demanding activities, such as high-performance sports, a PAL of 2.0 to 2.4 is used. This means that for an adult, normal weight male with a basal metabolic rate of 8,100 kilojoules per day, a total metabolic rate of 8,100 kJ x 2.4 = 19,440 is estimated for very heavy physical work. In this case, the power metabolic rate is 19,440 kJ (total metabolic rate) minus 8,100 kJ (basal metabolic rate) = 11,340 kJ. This corresponds to a power metabolism of 2,708 kilocalories. In well-trained people, the total metabolic rate can rise to about 50,000 kJ, corresponding to 11,900 kcal, in extreme cases.
Function and task
In dietetics, the main benefit that results from estimating power turnover or total turnover is the possibility of achieving a balanced energy balance through diet. In this context, a balanced energy balance means that the energy intake through the diet and the total consumption are balanced. If there is a sustained excess of energy intake, it is a positive energy balance, and if there is too little energy intake compared to consumption, it is a negative energy balance. For the approximate estimation of the individual basal metabolic rate, several formulas are available that take into account not only body mass but also gender, age and height. However, it must be noted that the basal metabolic rate can be subject to considerable fluctuations depending on hormone and metabolic status, so that the calculation of the total metabolic rate using the PAL factor is always only a rough estimate and approximation. For predominantly sedentary desk or screen activities with little compensatory sport, the PAL is 1.2 to 1.5. For running, the power requirement can also be estimated directly, depending on body weight and running distance. As an approximation, the energy requirement is assumed to be 4 kJ per kg body mass and per km distance. This means that an adult male with a body mass of 80 kg burns 4 kJ x 80 kg x 10 km = 3,200 kilojoules on a running distance of 10 km, equivalent to 764 kilocalories. Strictly speaking, the approximate formulas for energy consumption apply only to a metabolism that is in the individual normal mode. Humans have a starvation or emergency metabolism to which they switch when a negative energy balance of more than 500 kcal is reached in three consecutive days. This is a genetically fixed starvation metabolism program in which physiological processes are greatly slowed down and the basal metabolic rate can be reduced by up to about 50%. In developmental history, the emergency program was probably relevant for being able to survive times of scarce food supply better and longer.
Diseases and ailments
Power metabolic rate depends not only on the absolute amount of work done by the body or muscles over a unit of time, but on the efficiency with which the individual’s body metabolism uses the energy supply provided in the form of digestible carbohydrates, proteins, and fats. In healthy individuals with a stable cardiovascular system and a metabolic program that is in normal mode, the differences in power metabolic rate for the same activity are relatively small, so PAL values provide good approximations of power metabolic rate. A major influence on the power metabolic rate in the sense of an increase in efficiency, is the switching of the body’s metabolism to the starvation metabolism, which ensures longer survival in the case of a permanently low food supply. Although the performance of the muscles is somewhat reduced, the energy utilization of the body’s reserves is as efficient as possible. For the same amount of work performed, the power metabolic rate is reduced – similar to the basal metabolic rate. A deliberately induced deterioration in the efficiency of the basal and power metabolic rates can be achieved by eating very spicy foods. Above all, capsaicin, which is contained in chili, curry, hot peppers and cayenne pepper, among other things, leads to an acceleration of the metabolism with a reduction in the efficiency, and thus to a significant increase in the basal and power metabolic rate. This also explains the slimming effect of spicy foods, which offer fewer opportunities for the formation and storage of fat reserves for the same amount of energy in the form of digestible carbohydrates, fats and proteins. A number of diseases that affect the hormone balance have an influence on performance and basal metabolic rate in the sense of a dampening or accelerating effect. An example of this is hypothyroidism, the underactivity of the thyroid gland, which involves an insufficient release of thyroxine. Women experience similar hormonal incisions during menopause. The altered hormonal balance results in a lower basal and power metabolic rate, so women often experience unwanted weight gain if their eating patterns remain unchanged. A number of antidepressants have similar effects in the form of unwanted side effects.
