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.

Aerobic physical capacity plays an important role in reducing morbidity and mortality rates in subjects with cardiovascular diseases. This action is often related to an improvement in the autonomic modulation of heart rate variability (HRV). However, controversies remain regarding the effects of physical training on cardiac autonomic control in healthy subjects. Therefore, our objective was to investigate whether aerobic capacity interferes with the autonomic modulation of HRV and whether gender differences exist. Healthy men and women (N=96) were divided into groups according to aerobic capacity: low (VO₂: 22-38 ml/kg^-1 min^-1), moderate (VO₂: 38-48 ml/kg^-1 min^-1) and high (VO₂ >48 ml/kg^-1 min^-1.) We evaluated the hemodynamic parameters and body composition. The autonomic modulation of HRV was investigated using spectral analysis. This procedure decomposes the heart rate oscillatory signal into frequency bands: low frequency (LF=0.04-0.15Hz) is mainly related to sympathetic modulation, and high frequency (HF=0.15-0.5Hz) corresponds to vagal modulation. Aerobic capacity, regardless of gender, determined lower values of body fat percentage, blood pressure and heart rate. In turn, the spectral analysis of HRV showed that this parameter did not differ when aerobic capacity was considered. However, when the genders were compared, women had lower LF values and higher HF values than the respective groups of men. The results suggest that aerobic physical capacity does not interfere with HRV modulation; however, the cardiac modulatory balance differs between genders and is characterized by a greater influence of the autonomic vagal component in women and by the sympathetic component in men.

Background: Polycystic ovary syndrome (PCOS) is a common condition characterized by hyperandrogenism, anthropometric changes (increased weight and waist-to-hip ratio [WHR]), behavioral changes (sexual dysfunction, anxiety, and depression), and reduced quality of life. Physical exercise may reduce many of the adverse effects of PCOS. However, no studies have yet evaluated the effects of aerobic exercise on the sexual function of women with PCOS. Aim: To compare the effects of continuous and intermittent aerobic physical training on the sexual function and mood of women with PCOS. Methods: This is a secondary analysis of a controlled clinical trial in which women with PCOS (18–39 years of age) were randomly allocated to 1 of 3 groups for 16 weeks: continuous aerobic training (CAT, n = 23), intermittent aerobic training (IAT, n = 22), or no training (control group, n = 24). The Female Sexual Function Index (FSFI) was used to assess sexual function, and the Hospital Anxiety and Depression Scale (HADS) was used to assess anxiety and depression. Main Outcome Measure: The main outcome measure used was the FSFI. Outcomes: The primary outcomes were changes from baseline in total FSFI score and HAD scores at week 16 to prove the superiority of intermittent aerobic exercise compared with continuous aerobic exercise. Results: After 16 weeks, the CAT group had a significant increase in the total FSFI score, improvements in the FSFI domains of satisfaction and pain, and a reduction in the WHR. The CAT and IAT groups also had significantly lower levels of testosterone after 16 weeks. The IAT group had a significant increase in the total FSFI score and improvements in the desire, excitation, lubrication, orgasm, and satisfaction FSFI domains. The CAT and IAT groups both had significant reductions in anxiety and depression scores after 16 weeks. Clinical Implications: Aerobic physical training protocols could be indicated to promote mental and sexual health in women with PCOS. Strength & Limitations: This is one of the first studies to examine the effects of different physical training protocols on the sexual function of women with PCOS. The limitations of this study are that we did not consider diet or the frequency of sexual relations of participants with their partners. These factors could have interfered with the outcomes. Conclusion: The CAT and IAT protocols improved the sexual function and reduced the anxiety and depression of women with PCOS. Both protocols were similar to improve FSFI domain scores.

Heart rate variability (HRV), blood pressure variability (BPV), and baroreflex sensitivity (BRS) provide important information on cardiovascular autonomic control. However, little is known about the reorganization of HRV, BPV, and BRS after aerobic exercise. While there is a positive relationship between heart rate (HR) recovery rate and cardiorespiratory fitness, it is unclear whether there is a relationship between cardiorespiratory fitness and reorganization of cardiovascular autonomic modulation during recovery. Thus, this study aimed to investigate whether cardiorespiratory fitness influences the cardiovascular autonomic modulation recovery, after a cardiopulmonary exercise test. Sixty men were assigned into groups according to their cardiorespiratory fitness: low cardiorespiratory fitness (LCF = VO2: 22–38 mL kg⁻¹ min⁻¹), moderate (MCF = VO2: 38–48 mL kg⁻¹ min⁻¹), and high (HCF = VO2 > 48 mL kg⁻¹ min⁻¹). HRV (linear and non-linear analysis) and BPV (spectral analysis), and BRS (sequence method) were performed before and after a cardiopulmonary exercise test. The groups with higher cardiorespiratory fitness had lower baseline HR values and HR recovery time after the cardiopulmonary exercise test. On comparing rest and recovery periods, the spectral analysis of HRV showed a decrease in low-frequency (LF) oscillations in absolute units and high frequency (HF) in absolute and normalized units. It also showed increases in LF oscillations of blood pressure. Nonlinear analysis showed a reduction in approximate entropy (ApEn) and in Poincare Plot parameters (SD1 and SD2), accompanied by increases in detrended fluctuation analysis (DFA) parameters α1 and α2. However, we did not find differences in cardiovascular autonomic modulation parameters and BRS in relation to cardiorespiratory fitness neither before nor after the cardiopulmonary test. We concluded that cardiorespiratory fitness does not affect cardiovascular autonomic modulations after cardiopulmonary exercise test, unlike HR recovery.