Why is an elevated heart rate alone not always a valid indicator of an effective aerobic-training stimulus?
During aerobic exercise, an individual’s heart rate is a reliable indicator of how hard that individual is working. As the energy demands of the exercise increase, heart rate increases proportionately. Because the exercising muscles need more oxygen and fuel, an individual’s heart rate and stroke volume (i.e., the amount of blood pumped per beat) must increase to deliver more blood to the tissues to meet the increased metabolic needs of the active muscles. It is this increased metabolic demand that overloads the cardiorespiratory system and provides the necessary stimulus to improve aerobic exercise capacity. With resistance training, heart rate is disproportionately elevated relative to oxygen uptake. At any given level of oxygen uptake, heart rates are much higher for resistance training than for aerobic conditioning. The disproportionate rise in heart rate during resistance training is due to a phenomenon known as the pressor response, which is governed by the autonomic nervous syst
