<P> Heart rate is determined by the medulla oblongata and part of the pons, two organs located inferior to the hypothalamus on the brain stem . Heart rate is important for basal metabolic rate and resting metabolic rate because it drives the blood supply, stimulating the Krebs cycle . During exercise that achieves the anaerobic threshold, it is possible to deliver substrates that are desired for optimal energy utilization . The anaerobic threshold is defined as the energy utilization level of heart rate exertion that occurs without oxygen during a standardized test with a specific protocol for accuracy of measurement, such as the Bruce Treadmill protocol (see metabolic equivalent). With four to six weeks of targeted training the body systems can adapt to a higher perfusion of mitochondrial density for increased oxygen availability for the Krebs cycle, or tricarboxylic cycle, or the glycolitic cycle . This in turn leads to a lower resting heart rate, lower blood pressure, and increased resting or basal metabolic rate . </P> <P> By measuring heart rate we can then derive estimations of what level of substrate utilization is actually causing biochemical metabolism in our bodies at rest or in activity . This in turn can help a person to maintain an appropriate level of consumption and utilization by studying a graphical representation of the anaerobic threshold . This can be confirmed by blood tests and gas analysis using either direct or indirect calorimetry to show the effect of substrate utilization . The measures of basal metabolic rate and resting metabolic rate are becoming essential tools for maintaining a healthy body weight . </P>

Which is true of a person’s basal metabolic rate (bmr)