The amount of energy liberated by catabolism of food in the body is the same as the amount liberated when food is burned outside the body.
Energy released by catabolic processes in the body is used for maintaining bodily functions, digestion, food metabolism, thermal regulation and physical activity.
The amount of energy liberated per unit of time is the metabolic rate.
Isotonic muscle contractions perform work at peak efficiency, approximately at 50%.
Energy from isometric contractions appear as heat.
Energy storage is achieved by forming energy rich countdowns, and the amount of storage varies so that in the fasting state it is zero or negative.
Standard unit of heat energy is the calorie.
Energy released by combustion of foodstuffs can be measured by oxidizing compounds in a calorimeter.
Bomb calorimeter, refers to any metal vessels surrounded by water inside an insulated container and the food is ignited by an electric spark: the changing temperature of the water is a measure of the calories produced.
The calorie is defined as the amount of heat energy necessary to raise the temperature of 1 g of water 1° from 15°C to 16°C.
The resting metabolic rate is the largest contributor to total energy expenditure, 60-80%.
Resting metabolic rate is a relatively stable process within individuals with less than 5% daily variation, and variability between individuals is approximately 25%.
Resting metabolic rate is primarily determined by fat free mass which is approximately 63%, fat mass of approximately 6.7%, and age 1.7% with 25% of the variability unexplained.