<unk>  <unk>  is the amount of energy expended while at rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans). The release of energy in this state is sufficient only for the functioning of the vital organs, such as the heart, lungs, brain and the rest of the nervous system, liver, kidneys, sex organs, muscles and skin.<unk>  decreases with age and with the loss of lean body mass. Increased cardiovascular exercise and muscle mass can increase<unk> . Illness, previously consumed food and beverages, environmental temperature, and stress levels can affect one's overall energy expenditure, and can affect one's<unk>  as revealed by gas analysis.<unk>  is measured under very restrictive circumstances when a person is awake, but at complete rest. An accurate<unk>  measurement requires that the person's sympathetic nervous system is not stimulated.  A more common and closely related measurement, used under less strict conditions, is resting<unk>  rate (RMR).<unk>  and RMR are measured by gas analysis through either direct or indirect calorimetry, though a rough estimation can be acquired through an equation using age, sex, height, and weight. Studies of energy<unk> m using both methods provide convincing evidence for the validity of the respiratory quotient (R.Q.), which measures the inherent composition and utilization of carbohydrates, fats and proteins as they are converted to energy substrate units that can be used by the body as energy.
Basal metabolic rate
Cardiac output
Mean arterial pressure
Exercise capacity
Glomerular filtration rate
Coronary flow reserve
Respiratory rate
Renal blood flow