Heart rate

Abstract Key Points: • At peak exercise, normal subjects will usually reach near (>80%) to their predicted maximum HR: cardiac output is what determines their exercise capacity. • Unfit subjects and those with heart disease may also reach >80% of the predicted maximum HR, but their VO2max will be low. • If the maximum exercise HR is lower than expected, then: • the subject did not try very hard, or • something other than the heart (e.g. the lungs) is limiting exercise capacity, or • there may be a problem with the pacing response of the heart (‘chronotropic incompetence’), or the subject is on a beta-blocker. • A primary cardiac stroke volume problem can result in a rapidly rising HR, which is not sufficient to maintain cardiac output; the subject may be forced to stop before the HR reaches 80% of the predicted value. • Evaluating the graphical relationship between VO2 and HR provides valuable insight regarding the cause of exercise limitation.