Basal metabolic rate be elevated in stress, illness, and diabetes. Menopause may also affect metabolism. 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
Heart rate monitor watches, smart bands and cell phones often use PPG sensors. Garmin, Polar, Suunto and Fitbit are vendors selling consumer heart rate products. Most companies use their own proprietary Heart Rate algorithms. Garmin and other Smart Watch companies use technology from Firstbeat The newer, wrist based heart rate monitors have achieved almost identical levels of accuracy as their chest strap counterparts with independent tests showing up to 98% accuracy. Optical devices when used with rigorous activity can be less accurate or when used under water. Currently Heart rate variability is less available on optical devices. The Apple watch now includes HRV.