Final answer:
The metabolic rate measures the energy used by the body over a set time, primarily during rest known as basal metabolic rate (BMR), which depends on various factors, including muscle mass, and is related to oxygen consumption.
So, the correct answer is C) energy used in a given period of time.
Step-by-step explanation:
The metabolic rate is a measurement of the energy used by the body in a given period of time. When discussing the resting state, this is referred to as the basal metabolic rate (BMR), which indicates the total energy conversion rate of a person at rest. The BMR accounts for approximately 75% of the calories burned daily, as it fuels basic bodily functions and is dependent on factors such as age, gender, body weight, and muscle mass.
High levels of muscle mass, which burns more calories than body fat, contribute to a higher BMR; this is often seen in athletes. It is pertinent to note that energy consumption is directly proportional to the oxygen consumption, and during activities such as exercise, energy consumption increases significantly.
So, the correct answer is C) energy used in a given period of time.