Heart rate variability is an increasingly popular measure of cardiovascular health. Heart rate variability is known to decline with age, but to what degree is this a reflection of processes of cardiovascular aging versus the loss of physical fitness that is a feature of old age in our present, overly sedentary societies? This remains an open question, and an important one, given the range of evidence for exercise programs, and thus increased physical fitness, to be as effective as many medical interventions when it comes to improving cardiovascular health and reducing mortality in later life. Yes, aging causes an inevitable decline in physical condition, but living a sedentary lifestyle certainly speeds up that process.
Fluctuation analysis in intervals between heartbeats provides important indices related to autonomic modulation of heart rate variability (HRV). These indices are considered predictors of morbidity and mortality as they are frequently altered in patients with chronic degenerative diseases, especially in those with cardiovascular and metabolic diseases. Similarly, a reduction in HRV is common with aging. In all cases, cardiovascular fitness is often reduced to below the predicted values.
In turn, increases in cardiovascular fitness through regular physical exercise, especially aerobic exercise, represent an important therapeutic tool capable of promoting positive adjustments in cardiac autonomic modulation. These adjustments are characterized by reduced sympathetic modulatory influence and/or increased vagal modulatory influence on the heart, increasing the HRV. Therefore, several methodological tools have been used to assess the degree of impairment of autonomic modulation and the therapeutic effects of physical exercise.
In summary, there is a close relationship between cardiovascular fitness and HRV. This relationship was more evident in patients with cardiovascular and metabolic diseases and in aging, especially in those whose cardiovascular fitness and HRV were below the predicted values for age and sex. The challenge is to develop techniques and interpretation of increasingly accurate data, as well as standardizing the application of these techniques.