The relationship of the heart rate during exercise testing and the heart rate during daily living in subjects free of heart disease: Effects of age

Ninety-four subjects free of heart disease as verified by invasive and noninvasive testing underwent 24-hour ambulatory electrocardiography (ECG) and exercise testing. Maximum heart rate (HR_max), which was studied by exercise testing or by ambulatory ECG, decreased with similar slopes (-0.52 and -0.56 beats/mini/year, respectively). A positive correlation between HR_maxduring exercise testing and ambulatory ECG was observed (r = .43, P = .0034). Increasing age was associated with lower exercise tolerance (r = .39, P = .0104), and probably as a result of decreased exercise tolerance, with higher submaximal HR (r = .35, P = .0213) and higher increments of HR during submaximal exercise (r = .33, P = .0301). During daily activities, older individuals performed less strenuous activities (compared with exercise at 4 METs on the treadmill) than did younger subjects (r = .48, P = .0033). Minimum HR, as recorded by ambulatory ECG, was not affected by age (r = .03, P = .8147), probably because of the counterbalancing effects of a decline in the "intrinsic" HR and because of lower exercise tolerance associated with higher minimum HR (r = .32, P = .0355). Similarly, the average HR (total beats/hour or day) did not decline with age, although older individuals performed less strenuous activities because of their higher increments of HR during submaximal exercise. This is probably the result of deconditioning, since older individuals had lower exercise tolerance (r = .39, P = .0104), and lower exercise tolerance was associated with high submaximal HR (e.g., r = - .54, P = .0002 at 4 METs) and higher increments of HR at submaximal exercise (r = -.51, P = .0005). Increasing age was also associated with a lower increment of HR during maximum exercise (r = -.36, P = .0149) and a smaller difference between maximum and minimum HR recorded by ambulatory ECG (r = -.27, P = .0160).