Heart Rate Variability and Cardiovascular Fitness: What We Know so Far

Abstract

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 contrast, establishment of strict protocols in experimental design is a main challenge in establishing HRV analysis as a robust parameter for evaluating cardiovascular homeostasis. Thus, this review aimed to contribute to the understanding of autonomic modulation of HRV and its relationship with cardiovascular fitness, highlighting the advances made thus far, the applicability of analysis tools, and the confounding factors observed frequently.

Keywords: cardiovascular fitness; heart rate variability.

Figure 1

Representative illustration of heart rate variability parameters through spectral analysis in normotensive (A and C) and hypertensive (B and D) men obtained in our laboratory, before and after 16 weeks of aerobic physical training. The RR intervals (RRi) in absolute units (ms²) time series are illustrated by the line chart and was used the low-frequency (LF) and high-frequency (HF) bands in normalized units (nu) to indicated the relationship between autonomic modulation balance by the pie chart.

Figure 2

Representative illustration of heart rate variability parameters through spectral analysis in normotensive men (A and C) and women (B and D) obtained in our laboratory, before and after 16 weeks of aerobic physical training. The RR intervals (RRi) in absolute units (ms²) time series are illustrated by the line chart and was used the low-frequency (LF) and high-frequency (HF) bands in normalized units (nu) to indicated the relationship between autonomic modulation balance by the pie chart.