<unk>  <unk>  is the rate of energy expenditure per unit time by endothermic animals at rest. It is reported in energy units per unit time ranging from watt (joule/second) to ml O2/min or joule per hour per kg body mass J/(h·kg). Proper measurement requires a strict set of criteria to be met. These criteria include being in a physically and psychologically undisturbed state and being in a thermally neutral environment while in the post-absorptive state (i.e., not actively digesting food). In bradymetabolic animals, such as fish and reptiles, the equivalent term standard<unk>  rate (SMR) applies. It follows the same criteria as<unk> , but requires the documentation of the temperature at which the<unk>  rate was measured. This makes<unk>  a variant of standard<unk>  rate measurement that excludes the temperature data, a practice that has led to problems in defining "standard" rates of<unk> m for many mammals.<unk> m comprises the processes that the body needs to function.<unk>  is the amount of energy per unit of time that a person needs to keep the body functioning at rest. Some of those processes are breathing, blood circulation, controlling body temperature, cell growth, brain and nerve function, and contraction of muscles.<unk>  affects the rate that a person burns calories and ultimately whether that individual maintains, gains, or loses weight. The<unk>  accounts for about 60 to 75% of the daily calorie expenditure by individuals. It is influenced by several factors. In humans,<unk>  typically declines by 1–2% per decade after age 20, mostly due to loss of fat-free mass, although the variability between individuals is high.
Basal metabolic rate
Basal body temperature
Heart rate variability
Basal rate
Electrodermal activity
Glycemic index
Cardiac reserve
Renal threshold