heart rate (HR)

heart rate (HR)

the number of heart beats per minute, ranging typically from a resting heart rate of 60-75 (but can be less than 50, especially in trained endurance athletes) to a maximal heart rate in exercise that depends on fitness and age (average guide: 220 minus years of age). Regulated by the balance between sympathetic and parasympathetic influences on the pacemaker (sinoatrial node). See also cardiac output.