Final answer:
The basal metabolic rate (BMR) is the energy expended by the body at rest to maintain basic physiological functions, accounting for the majority of daily energy use, and varies by factors such as muscle mass and activity level.
Step-by-step explanation:
The amount of energy expended by the body to meet its basic physiological needs is known as the basal metabolic rate (BMR). This rate measures how much energy the body requires at rest for basic functions like those of the organs, and it accounts for about 75% of the daily caloric expenditure. BMR factors include age, gender, body weight, and muscle mass, with muscle mass having a higher energy demand, resulting in a higher BMR for athletes. In addition to maintaining bodily functions, the body also expends energy through physical activity and thermoregulation. During vigorous exercise, energy consumption increases significantly, especially in skeletal muscles and the heart. Energy consumption is also connected to oxygen use; for example, every liter of oxygen consumed is roughly equivalent to 20 kJ of energy.