Influence of exercise training on heart rate variability in post-menopausal women with elevated arterial blood pressure

Effects of aging and endurance exercise training on cardiorespiratory fitness and cardiac structure and function in healthy midlife and older women

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality in women in developed societies. Unfavorable structural and functional adaptations within the heart and central blood vessels with sedentary aging in women can act as the substrate for the development of debilitating CVD conditions such as heart failure with preserved ejection fraction (HFpEF). The large decline in cardiorespiratory fitness, as indicated by maximal or peak oxygen uptake (V̇o2max and V̇o2peak, respectively), that occurs in women as they age significantly affects their health and chronic disease status, as well as the risk of cardiovascular and all-cause mortality. Midlife and older women who have performed structured endurance exercise training for several years or decades of their adult lives exhibit a V̇o2max and cardiac and vascular structure and function that are on par or even superior to much younger sedentary women. Therefore, regular endurance exercise training appears to be an effective preventative strategy for mitigating the adverse physiological cardiovascular adaptations associated with sedentary aging in women. Herein, we narratively describe the aging and short- and long-term endurance exercise training adaptations in V̇o2max, cardiac structure, and left ventricular systolic and diastolic function at rest and exercise in midlife and older women. The role of circulating estrogens on cardiac structure and function is described for consideration in the timing of exercise interventions to maximize beneficial adaptations. Current research gaps and potential areas for future investigation to advance our understanding in this critical knowledge area are highlighted.

Effect of Physical Exercise on Cardiac Autonomic Modulation in Hypertensive Individuals: A Systematic Review and Meta-analysis

BACKGROUND

Cardiac autonomic dysfunction is associated with hypertension and exercise training (ET) in healthy individuals is found to improve cardiac autonomic modulation (CAM). However, the effects of physical exercise on CAM in hypertensive individuals are under debate.

OBJECTIVE

The aim of the review is to systematically evaluate the literature on the effects of physical exercise on CAM in hypertensive individuals and analyse comparative differences in the effects of exercise between hypertensive and normotensive individuals.

METHODS

Electronic databases, such as Pubmed, PEDro, Scopus, and Web of Science, were systematically searched from inception up to February, 2022, evaluating the effect of ET on CAM either by heart rate variability (HRV), baroreflex sensitivity or heart rate recovery. Fifteen studies were included in the review. The risk of bias was assessed using the Cochrane risk of bias tool version 2 and the risk of bias in studies of intervention (ROBINS-I) tool. The overall quality of evidence was assessed using the grading of recommendations, assessment, development, and evaluation approach. Ten studies were included in the quantitative analysis. The meta-analysis and sensitivity analysis were performed using review manager 5.4.1; publication bias was assessed using Jamovi 2.2.5 software.

RESULTS

The qualitative analysis revealed low to moderate certainty of evidence for ET and moderate for aerobic training. For the effect of overall ET, the analysis revealed that the standardized mean differences (SMD) showed a significant effect of ET on HF (SMD 1.76, p = 0.04) and RMSSD (SMD 1.19, p < 0.0001) and a significant decrease in LF (SMD -1.78, p = 0.04). Aerobic training revealed nonsignificant improvement in HRV parameters. In the comparative analysis, ET did not show a significant difference in improvement between hypertensive and normotensive individuals.

CONCLUSION

This review suggests an improvement in CAM with physical exercise in hypertensive individuals, but the overall effect of ET in hypertensive individuals must be interpreted with caution as the robustness of the data is compromised in the sensitivity analysis of the trials. High-quality future trials focusing on different modes of ET interventions are needed to strengthen the findings of the present review.

Heart rate variability as a function of menopausal status, menstrual cycle phase, and estradiol level

Low estradiol status is associated with increased cardiovascular risk. We sought to determine the association between heart rate variability (HRV), a marker of cardiovascular risk, at baseline and in response to stressor as a function of menopausal status, menstrual cycle phase and estradiol level. Forty-one healthy women (13 postmenopausal, 28 premenopausal) were studied. Eleven premenopausal women were additionally studied in the high and low estradiol phases of the menstrual cycle. HRV was calculated by spectral power analysis (low Frequency (LF), high frequency (HF) and LF:HF) at baseline and in response to graded Angiotensin II (AngII) infusion. The primary outcomes were differences in HRV at baseline and in response to AngII. Compared to premenopausal women in the low estradiol phase, postmenopausal women demonstrated lower baseline LF (p = 0.01) and HF (p < 0.001) measures, which were not significant after adjustment for age and BMI. In response to AngII, a decrease in cardioprotective HRV (ΔHF = -0.43 ± 0.46 ln ms² , p = 0.005 vs. baseline) was observed in postmenopausal women versus premenopausal women. Baseline HRV parameters did not differ by menstrual phase in premenopausal women. During the low estradiol phase, no differences were observed in the HRV response to AngII challenge. In contrast, women in the high estradiol phase were unable to maintain HRV (ΔLF = -0.07 ± 0.46 ln ms² , p = 0.048 response vs. baseline, ΔHF = -0.33 ± 0.74 ln ms2, p = 0.048 response vs. baseline). No association was observed between any measure of HRV and estradiol level. Menopausal status and the high estradiol phase in premenopausal women were associated with reduced HRV, a marker of cardiovascular risk. Understanding the role of estradiol in the modulation of cardiac autonomic tone may help guide risk reduction strategies in women.

Exercise dose-response relationship with heart rate variability in individuals with overweight and obesity: protocol for a systematic review and meta-analysis of randomised controlled trials

INTRODUCTION

Obesity is a chronic relapsing disease process and serious public health concern that can lead to chronic diseases, medical complications and a higher risk of disability. Another significant feature of obesity is dysfunction in cardiac autonomic function, which leads to changes in parasympathetic and sympathetic regulation, which can be measured using heart rate variability (HRV). The objective of this review is to estimate the extent to which exercise doses impacts on HRV among individuals living with overweight and obesity class I and II.

METHODS AND ANALYSIS

A systematic literature search will be performed using PubMed/Medline, Scopus, EMBASE, ProQuest, CINAHL, Web of Science and the Cochrane Library for articles dating from 1965 to December 2021. Inclusion criteria include studies designed as parallel-arm randomised trials, enrolling adolescent and adult individuals with overweight (body mass index, BMI≥25 to ≤29.9) and obesity (class I BMI: 30-34.9 and class II BMI: 35-39.9) undergoing aerobic or resistance training or concurrent exercise training. For data synthesis, sensitivity analysis, subgroup analysis and risk of bias assessment, Stata V.13.0 software will be used.

ETHICS AND DISSEMINATION

Formal ethical approval is not required. This systematic review will be submitted to a peer-reviewed journal.

PROSPERO REGISTRATION NUMBER

CRD42019104154.

Habitual aerobic exercise in healthy postmenopausal women does not augment basal cardiac autonomic activity yet modulates autonomic-metabolic interactions

OBJECTIVES

The aim of the present study was to examine the effects of habitual exercise training and metabolic health on basal cardiac autonomic function and cardiac autonomic recovery after exercise in healthy postmenopausal women (PMW).

METHODS

Habitually aerobically trained PMW (PMW-tr; 56 ± 1y; n = 11), and untrained PMW (PMW-un; 57 ± 1y; n = 13) and premenopausal women (PreM; ages 26 ± 1y; n = 14) were studied. Cardiac autonomic function, assessed using heart rate variability (HRV), was measured before and one hour after 45-minutes of moderate-intensity exercise (60% VO2peak). Fast Fourier frequency domain measures of high (HF; 0.15 Hz-0.4 Hz), low (LF; 0.04 Hz-0.15 Hz), very low (VLF; 0.01 Hz-0.04 Hz), and Total (VLF+LF+HF) HRV were assessed. Serum estradiol, insulin, and glucose were determined, and HOMA-IR, an index of insulin resistance, was calculated.

RESULTS

In PMW groups, body composition and serum markers did not differ (P>0.05). Pre-exercise, heart rate was lower (P<0.05) in PMW-tr than PMW-un, yet HRV did not differ (P>0.05). In PMW-tr only, HF was inversely associated (P<0.05) with insulin (r = -0.738) and HOMA-IR (r = -0.758). In PreM, HRV was higher than PMW (P<0.05) and was positively correlated with estradiol (P<0.05). Postexercise, HRV was decreased within all groups (P<0.05) yet remained higher in PreM (P<0.05), and similar (P>0.05) between PMW.

CONCLUSION

Basal and postexercise HRV does not differ between habitually aerobically trained and untrained PMW. However, greater insulin sensitivity was associated with higher cardiac parasympathetic tone in trained PMW only. Exercise training may favorably modulate cardiac autonomic-metabolic interactions in PMW.

PHYSICAL TRAINING IN ATHLETES: ANALYSIS OF CARDIAC AUTONOMIC MODULATION

ABSTRACT Introduction Cardiac autonomic modulation (CAM) is a result of the balance between the sympathetic and parasympathetic systems. This interaction results in heart rate variation (HRV), analyzed by specific electrocardiographic parameters. These parameters are modified by the practice of physical activity, indicating better cardiac conditioning. Objectives To evaluate the cardiac autonomic modulation of athletes of the XXVIII Ecological Walk at two separate times during their period of physical training. Also, to link the practice of physical activity with stress reduction in these individuals. Methods 24-hour Holter exams were performed at two times (before and after a 2-month period of non-standard physical training), and the results were analyzed using the software programs Epi-Info 7 and BioEstat 5.0. Inferential analysis was performed by the nonparametric Shapiro-Wilk test. Statistical significance was assigned to p values less than 0.05, with 95% confidence interval (95% CI). Results The sample was mostly male (n = 14; 77.78%), with a mean age of 49.55 years. No individual trained for less than 60 days; most (47.06%) trained for 151-200 days, with walking being the predominant modality (64.71%). No statistically significant difference was found in the parameters HRV pNN50 (p = 0.18), rMSSD (p = 0.14) or HF (p = 0.117) after the evaluated training period. Conclusions Participants who are longtime sportsmen and physically active showed parasympathetic saturation, therefore, they did not show significant changes in HRV. Also, low levels of stress were observed in those who practiced physical activity. Level of evidence II; Prognosis Study.

Comparison of performance and health indicators between perimenopausal and postmenopausal obese women: the effect of high-intensity interval training (HIIT)

OBJECTIVE

This study examined the effects of 6 weeks of high-intensity interval training (HIIT) on performance and health indicators in obese perimenopausal (PERIM) women and similarly aged and older postmenopausal women (POSTM1 and POSTM2, respectively).

METHODS

Sixteen PERIM women (average age 49.6 y), 21 POSTM1 women (average age 50.6 y), and 19 POSTM2 women (average age 69.6 y) completed a 6-week HIIT intervention. Anthropometric parameters, mechanical efficiency (ME in %), lipid oxidation (LO in %), and low and high spectral frequencies (LF[ms2] and HF[ms2]) were computed pre- and postintervention.

RESULTS

PERIM women showed a significantly higher VO2max preintervention compared to POSTM1 and 2 (P < 0.01). Moreover, HF, LF, and the LF/HF ratio differed significantly in PERIM women preintervention compared to POSTM1 and 2 (P < 0.01, respectively). After 6 weeks, a significant decrease in anthropometric variables was observed for all groups (P < 0.01). The VO2max in mL/kg/min increased for all groups (P < 0.01). Multiple linear regression analysis demonstrated that age contributed significantly to differences in VO2max values between groups preintervention (r = 0.72). This model accounted for 34% (r2 = 0.34) of the variation. On the other hand, menopause status was an independent predictor of LO, accounting for 38% of the variation, as well as of HF (33%), LF (29%), and the LF/HF ratio (24%). After HIIT, no age or menopause effect was detected for these independent variables.

CONCLUSIONS

Maximal oxygen consumption, HF, LF, and the LF/HF ratio differ among women according to the menopausal status and age. A 6-week HIIT intervention improved many health and performance parameters and reduced the effects of menopause and age.

Heart rate variability responses to a combined exercise training program: correlation with adiposity and cardiorespiratory fitness changes in obese young men

Although the influence of adiposity indices and cardiorespiratory fitness (CRF) on heart rate variability (HRV) has been demonstrated extensively, the causal link between the changes in adiposity as well as in CRF and the alterations in cardiac autonomic function is unclear. Thus, this study aimed to assess the correlation between the changes in adiposity and CRF and the alterations in HRV after 12-week exercise training. Twenty obese sedentary men aged 20.5±1.2 years were randomly assigned into 2 groups (n=10 each): the control (CG) and the exercise group (EG). The EG trained 60 min of combined aerobic, anaerobic and strengthening exercise, 4 sessions/wk for 12 weeks, whilst the CG remained relatively inactive. Measurements of resting HRV, body composition, and peak oxygen consumption (VO_2peak) were obtained at baseline and after the 12-week training program. Compared with CG, the exercise training significantly reduced adiposity indices and improved vagal-related HRV variables and VO_2peak. Significant correlations were observed between changes in HRV variables and adiposity indices and VO_2peak changes. Stepwise regression analysis revealed that changes in a Poincaré plot index (SD1/SD2 ratio) predicted 32.4% of the variance in the relative VO_2peak changes. These findings suggest that obese sedentary young men achieved significant improvements in vagal activity, adiposity indices and aerobic fitness after the exercise training. The higher reduction in fat mass, especially central obesity, the greater alteration of vagal modulation. Moreover, the alteration in resting HRV is a possible predictor for adaptations to exercise training in obese sedentary young men.

Differences in nonlinear heart dynamics during rest and exercise and for different training

OBJECTIVE

In this work we want to analyze differences in nonlinear properties between rest and exercise and also to study the permanent effects of physical exercise on heart rate dynamics.

APPROACH

It has been shown that physical exercise alters heart dynamics by increasing heart rate and decreasing variability, modifying spectral power and linear correlations, etc. We hypothesize that physical exercise should also reduce nonlinearity in the heartbeat time series. To quantify nonlinearity in the heartbeat time series, we use an index of nonlinearity recently proposed by Bernaola et al based on correlations of the magnitude time series.

MAIN RESULTS

Our results confirm our initial hypothesis of loss of nonlinearity during physical exercise. Moreover, regarding the permanent effects of physical exercise on heart rate dynamics, we also obtain that aerobic physical training tends to increase nonlinearity in heart dynamics during rest.

SIGNIFICANCE

It is well-known that heart dynamics are controlled by complex interactions between the sympathetic and parasympathetic branches of the autonomic nervous system. Moreover, these two branches act in a competing way, resulting in a clear parasympathetic withdrawal and sympathetic activation during physical exercise. We associate these interactions during physical exercise with a drastic loss of nonlinear properties in the heartbeat time series, revealing the importance of nonlinearity measures in the study of complex systems.

Estimated aortic stiffness is independently associated with cardiac baroreflex sensitivity in humans: role of ageing and habitual endurance exercise

We hypothesized that differences in cardiac baroreflex sensitivity (BRS) would be independently associated with aortic stiffness and augmentation index (AI), clinical biomarkers of cardiovascular disease (CVD) risk, among young sedentary and middle-aged/older sedentary and endurance-trained adults. A total of 36 healthy middle-aged/older (age 55-76 years, n=22 sedentary; n=14 endurance-trained) and 5 young sedentary (age 18-31 years) adults were included in a cross-sectional study. A subset of the middle-aged/older sedentary adults (n=12) completed an 8-week aerobic exercise intervention. Invasive brachial artery blood pressure waveforms were used to compute spontaneous cardiac BRS (via sequence technique) and estimated aortic pulse wave velocity (PWV) and AI (AI, via brachial-aortic transfer function and wave separation analysis). In the cross-sectional study, cardiac BRS was 71% lower in older compared with young sedentary adults (P<0.05), but only 40% lower in older adults who performed habitual endurance exercise (P=0.03). In a regression model that included age, sex, resting heart rate, mean arterial pressure (MAP), body mass index and maximal exercise oxygen uptake, estimated aortic PWV (β±SE = −5.76 ± 2.01, P=0.01) was the strongest predictor of BRS (Model R²=0.59, P<0.001). The 8 week exercise intervention improved BRS by 38% (P=0.04) and this change in BRS was associated with improved aortic PWV (r=−0.65, P=0.044, adjusted for changes in MAP). Age- and endurance exercise-related differences in cardiac BRS are independently associated with corresponding alterations in aortic PWV among healthy adults, consistent with a mechanistic link between variations in the sensitivity of the baroreflex and aortic stiffness with age and exercise.

The influence of reduced insulin sensitivity via short-term reductions in physical activity on cardiac baroreflex sensitivity during acute hyperglycemia

Reduced insulin sensitivity and impaired glycemic control are among the consequences of physical inactivity and have been associated with reduced cardiac baroreflex sensitivity (BRS). However, the effect of reduced insulin sensitivity and acute hyperglycemia following glucose consumption on cardiac BRS in young, healthy subjects has not been well characterized. We hypothesized that a reduction in insulin sensitivity via reductions in physical activity would reduce cardiac BRS at rest and following an oral glucose tolerance test (OGTT). Nine recreationally active men (23 ± 1 yr; >10,000 steps/day) underwent 5 days of reduced daily physical activity (RA5) by refraining from planned exercise and reducing daily steps (<5,000 steps/day). Spontaneous cardiac BRS (sequence technique) was compared at rest and for 120 min following an OGTT at baseline and after RA5. A substudy (n = 8) was also performed to independently investigate the influence of elevated insulin alone on cardiac BRS using a 120-min hyperinsulinemic-euglycemic clamp. Insulin sensitivity (Matsuda index) was significantly reduced following RA5 (BL 9.2 ± 1.3 vs. RA5 6.4 ± 1.1, P < 0.001). Resting cardiac BRS was unaffected by RA5 and significantly reduced during the OGTT similarly at baseline and RA5 (baseline 0 min, 28 ± 4 vs. 120 min, 18 ± 4; RA5 0 min, 28 ± 4 vs. 120 min, 21 ± 3 ms/mmHg). Spontaneous cardiac BRS was also reduced during the hyperinsulinemic-euglycemic clamp (P < 0.05). Collectively, these data demonstrate that acute elevations in plasma glucose and insulin can impair spontaneous cardiac BRS in young, healthy subjects, and that reductions in cardiac BRS following acute hyperglycemia are unaffected by reduced insulin sensitivity via short-term reductions in physical activity.

Heart rate variability and swimming

BACKGROUND AND OBJECTIVES

Professionals in the domain of swimming have a strong interest in implementing research methods in evaluating and improving training methods to maximize athletic performance and competitive outcome. Heart rate variability (HRV) has gained attention in research on sport and exercise to assess autonomic nervous system activity underlying physical activity and sports performance. Studies on swimming and HRV are rare. This review aims to summarize the current evidence on the application of HRV in swimming research and draws implications for future research.

METHODS

A systematic search of databases (PubMed via MEDLINE, PSYNDEX and Embase) according to the PRISMA statement was employed. Studies were screened for eligibility on inclusion criteria: (a) empirical investigation (HRV) in humans (non-clinical); (b) related to swimming; (c) peer-reviewed journal; and (d) English language.

RESULTS

The search revealed 194 studies (duplicates removed), of which the abstract was screened for eligibility. Fourteen studies meeting the inclusion criteria were included in the review. Included studies broadly fell into three classes: (1) control group designs to investigate between-subject differences (i.e. swimmers vs. non-swimmers, swimmers vs. other athletes); (2) repeated measures designs on within-subject differences of interventional studies measuring HRV to address different modalities of training or recovery; and (3) other studies, on the agreement of HRV with other measures.

CONCLUSIONS

The feasibility and possibilities of HRV within this particular field of application are well documented within the existing literature. Future studies, focusing on translational approaches that transfer current evidence in general practice (i.e. training of athletes) are needed.

AD, Costa FSM, Bianchi AM. Are Complexity Metrics Reliable in Assessing HRV Control in Obese Patients During Sleep?

Obesity is associated with cardiovascular mortality. Linear methods, including time domain and frequency domain analysis, are normally applied on the heart rate variability (HRV) signal to investigate autonomic cardiovascular control, whose imbalance might promote cardiovascular disease in these patients. However, given the cardiac activity non-linearities, non-linear methods might provide better insight. HRV complexity was hereby analyzed during wakefulness and different sleep stages in healthy and obese subjects. Given the short duration of each sleep stage, complexity measures, normally extracted from long-period signals, needed be calculated on short-term signals. Sample entropy, Lempel-Ziv complexity and detrended fluctuation analysis were evaluated and results showed no significant differences among the values calculated over ten-minute signals and longer durations, confirming the reliability of such analysis when performed on short-term signals. Complexity parameters were extracted from ten-minute signal portions selected during wakefulness and different sleep stages on HRV signals obtained from eighteen obese patients and twenty controls. The obese group presented significantly reduced complexity during light and deep sleep, suggesting a deficiency in the control mechanisms integration during these sleep stages. To our knowledge, this study reports for the first time on how the HRV complexity changes in obesity during wakefulness and sleep. Further investigation is needed to quantify altered HRV impact on cardiovascular mortality in obesity.

Assessment of Risk Factor for Cardiovascular Disease Using Heart Rate Variability in Postmenopausal Women: A Comparative Study between Urban and Rural Indian Women

Cardiovascular diseases are important causes of morbidity and mortality in postmenopausal women. A major determinant of cardiovascular health is the status of autonomic nervous system and assessment of Heart Rate Variability (HRV). Heart Rate Variability is a noninvasive and sensitive technique to evaluate cardiovascular autonomic control. Reduced HRV is an independent risk factor for the development of heart disease. This study evaluated the risk factors for cardiovascular diseases using HRV, between urban and rural Indian postmenopausal women ranging in age from 40 to 75 years. Findings of the analysis of HRV have showed that the total power which reflects overall modulation of cardiac autonomic activity (759 ± 100  versus 444 ± 65), the absolute power of high frequency which is surrogate of cardiovagal activity (247 ± 41  versus 163 ± 45), and low frequency that reflects cardiac sympathetic activity (205 ± 26  versus 127 ± 18) were significantly higher in urban women than that of their rural counterparts. Further, among the anthropometric measures, waist circumference was significantly correlated with indices of HRV. The study concludes that rural Indian women are associated with an additional risk beyond that of ageing and postmenopausal status when compared to the urban women. The higher central obesity could be the contributing factor for developing higher risk for cardiovascular disease among the rural women.

Design and methods of a multi-site, multi-behavioral treatment trial for menopausal symptoms: the MsFLASH experience

BACKGROUND

Behavioral strategies are recommended for menopausal symptoms, but little evidence exists regarding efficacy.

PURPOSE

Describe design and methodology of a randomized controlled 3 by 2 factorial trial of yoga, exercise and omega-3 fatty acids.

METHODS

Women from three geographic areas with a weekly average of ≥14 hot flashes/night sweats, who met exclusion/inclusion criteria, were randomized to 12weeks of: 1) yoga classes and daily home practice; 2) supervised, facility-based aerobic exercise training; or 3) usual activity. Women in each arm were further randomized to either omega-3 supplement or placebo. Standardized training, on-going monitoring, and site visits were adopted to ensure consistency across sites and fidelity to the intervention. Participant adherence to the intervention protocol was monitored continuously, and retention was actively encouraged by staff. Information on adverse events was systematically collected.

RESULTS

Of 7377 women who responded to mass mailings, 355 (4.8%) were randomized; mean age was 54.7 (sd=3.7), 26.2% were African American, 81.7% were post-menopausal, and mean baseline frequency of daily hot flashes/night sweats was 7.6 (sd=3.8). Adherence of ≥80% was 59% for yoga, 77% for exercise training, and 80% for study pills. Final week 12 data were collected from 95.2%

CONCLUSIONS

Conducting a multi-site, multi-behavioral randomized trial for menopausal symptoms is challenging but feasible. Benefits included cost-effective study design, centralized recruitment, and methodologic standardization.

Análise da correlação entre o protocolo Polar Fitness Test® para predição de VO2máx e ergoespirometria

INTRODUÇÃO: A importância da mensuração do consumo máximo de oxigênio (<img border=0 id="_x0000_i1026" src="/img/revistas/rbme/v18n3/v.jpg" align=absmiddle>O2máx)é justificada por sua aceitação internacional como o melhor parâmetro fisiológico para avaliar a capacidade funcional do sistema cardiorrespiratório tanto em atletas como em não atletas que treinam fisicamente com objetivo de obter melhor saúde. OBJETIVO: Verificar a concordância entre os protocolos Polar Fitness Test® para a estimativa do <img border=0 id="_x0000_i1027" src="/img/revistas/rbme/v18n3/v.jpg" align=absmiddle>O2máx e o teste de esforço máximo com medida direta de gases. MÉTODOS: Dezessete homens ativos (22,5 ± dois anos) participaram. Em repouso, aplicou-se o protocolo Polar Fitness Test® e, em seguida, a coleta direta de gases sob o esforço máximo, em esteira, seguindo o protocolo de Bruce. RESULTADOS: Houve diferença significativa entre os valores médios dos métodos para estimativa do <img border=0 id="_x0000_i1028" src="/img/revistas/rbme/v18n3/v.jpg" align=absmiddle>O2máx. O protocolo Polar Fitness Test® subestimou o <img border=0 id="_x0000_i1029" src="/img/revistas/rbme/v18n3/v.jpg" align=absmiddle>O2máx, em média 15% (IC95%: 24; -53%) comparado com a medida direta de gases. Os valores obtidos pelo Polar Fitness Test® não tiveram boa correlação com a medida direta em ergoespirômetro (r = 0,1). CONCLUSÃO: O protocolo Polar Fitness Test® não é válido para a estimativa do <img border=0 id="_x0000_i1030" src="/img/revistas/rbme/v18n3/v.jpg" align=absmiddle>O2máx em homens jovens ativos fisicamente.

Interaction between age and aerobic fitness in determining heart rate dynamics

Heart rate variability (HRV) and phase-rectified signal averaging (PRSA) estimates of heart rate dynamics are diminished in older people compared with younger people. However, it is not fully elucidated whether these differences are related to age per se or to the concomitant influence of aerobic fitness. Aerobic fitness (peak oxygen uptake, gas exchange threshold, oxygen uptake kinetics, exercise economy) was assessed in 70 healthy adults (41 male) aged 18-57 years. Participants also underwent a 24 h, ambulatory ECG for the derivation of HRV and PRSA variables. HRV was most sensitive to age and aerobic fitness when measured during the morning period (6 am-12 pm). HRV and PRSA were both diminished with age and were higher in aerobically superior participants. The decline in HRV with age was predominantly attributable to age itself (33%), with aerobic fitness representing an additional modulating factor. The present study also provides tentative evidence that assessment of the influence of aerobic fitness should not rely on [Formula: see text]O(2peak) alone. These findings demonstrate that age per se is an important factor in determining HRV. However, given the clinical importance of diminished HRV and the immutable nature of aging, the potential significance of physical activity/training to enhance cardiac regulatory function should not be underestimated.

Heart rate variability and exercise in aging women

BACKGROUND

Our group has shown a positive dose-response in maximal cardiorespiratory exercise capacity (VO(2max)) and heart rate variability (HRV) to 6 months of exercise training but no improvement in VO(2max) for women ≥60 years. Here, we examine the HRV response to exercise training in postmenopausal women younger and older than 60 years.

METHODS

We examined 365 sedentary, overweight, hypertensive, postmenopausal women randomly assigned to sedentary control or exercise groups exercising at 50% (4 kcal/kg/week, [KKW]), 100% (8 KKW) and 150% (12 KKW) of the National Institutes of Health (NIH) Consensus Development Panel physical activity guidelines. Primary outcomes included time and frequency domain indices of HRV.

RESULTS

Overall, our analysis demonstrated a significant improvement in parasympathetic tone (rMSSD and high frequency power) for both age strata at 8 KKW and 12 KKW. For rMSSD, the age-stratified responses were: control, <60 years, 0.20 ms, 95% confidence interval (CI)-2.40, 2.81; ≥60 years, 0.07 ms, 95% CI -3.64, 3.79; 4 KKW, <60 years, 3.67 ms, 95% CI 1.55, 5.79; ≥60 years, 1.20 ms, 95% CI -1.82, 4.22; 8-KKW, <60 years, 3.61 ms, 95% CI 0.88, 6.34; ≥60 years, 5.75 ms, 95% CI 1.89, 9.61; and 12-KKW, <60 years, 5.07 ms, 95% CI 2.53, 7.60; ≥60 years, 4.28 ms, 95% CI 0.42, 8.14.

CONCLUSIONS

VO(2max) and HRV are independent risk factors for cardiovascular disease (CVD) mortality. Despite no improvement in VO(2max), parasympathetic indices of HRV increased in women ≥60 years. This is clinically important, as HRV has important CVD risk and neurovisceral implications beyond cardiorespiratory function.

Exercício aeróbico no controle da hipertensão arterial na pós-menopausa

OBJETIVO: Avaliar o efeito do treinamento com exercício aeróbio na capacidade funcional (CF) e no controle da pressão arterial (PA), em mulheres na pós-menopausa, hipertensas estágio I, controladas ou não com tratamento medicamentoso, em uma Unidade Básica de Saúde (UBS). METODOLOGIA: Antes e após 12 semanas de treinamento com exercício aeróbio em uma UBS, dez mulheres hipertensas na pós-menopausa, idade de 56,9 ± 6 anos, sedentárias, não usuárias de terapia de reposição hormonal, foram submetidas à avaliação do índice de massa corporal (IMC); da circunferência da cintura (CC); da CF pelo teste ergométrico (maior consumo de oxigênio/ VO2 e tempo de teste) e teste de caminhada em seis minutos (distância caminhada); e das medidas casuais repetidas da PA. Reavaliações foram efetuadas a cada 30 dias. Os dados são expressos em média e desvio-padrão. Foram aplicados os testes de Kolmogorov-Smirnov, t de Student pareado, Wilcoxon e ANOVA para medidas repetidas, considerando significativo p < 0,05. RESULTADOS: Não houve diferença significativa no IMC (p = 0,40) e CC (p = 0,74) após a intervenção. Entretanto, após 30 dias observou-se redução da PA sistólica (de 142,70 ± 6,25 para 130,76 ± 5,80 mmHg, p < 0,001) e diastólica (de 87,03 ± 4,48 para 81,90 ± 4,30 mmHg, p = 0,002) e melhora da CF pelo VO2 (de 24,90 ± 6,38 para 27,82 ± 6,14 mL/kg/min, p = 0,028), tempo de teste (de 6,89 ± 1,78 para 7,7 ± 1,8 min, p = 0,022) e distância caminhada (de 511,07 ± 41,99 para 556,1 ± 43,19 m, p = 0,009). CONCLUSÃO: O programa de treinamento com exercício aeróbio em uma UBS mostrou-se efetivo e viável, contribuindo para a redução da PA e melhora da capacidade funcional em mulheres hipertensas na pós-menopausa.

Autonomic function and change in insulin for exercising postmenopausal women

PURPOSE

Obesity, physical inactivity and altered estrogen metabolism play an integrated role contributing to the disease risk profiles of postmenopausal women. These same risk factors also affect modulation of the autonomic nervous system (ANS).

METHODS

We examined 332 postmenopausal, overweight, previously sedentary women (mean+/-SD; age, 57.6+/-6.3 years; weight, 84.3+/-11.9kg; BMI, 31.7+/-3.7kg/m(2)) participating in a 6-month, moderate intensity, aerobic exercise training intervention to determine the relationship between heart rate variability (HRV) derived autonomic function and fasting insulin. We analyzed quartiles of change in time and frequency domain indices of ANS activity and changes in insulin for between and within group differences using ANCOVA and Tukey post hoc tests adjusted for age, ethnicity, randomization group, change in fitness, and change in weight.

RESULTS

We observed at baseline that insulin was positively correlated with body anthropometry (body weight, r(2)=0.34; BMI, r(2)=0.39; waist circumference, r(2)=0.29; all, P<0.001), and inversely associated with rMSSD (r(2)=-0.12) and SDNN (r(2)=-0.18; all, P<0.01). After the intervention, changes in rMSSD (r(2)=-0.21, P<0.002) and SDNN r(2) -0.19, P<0.0001) were inversely correlated to insulin change. Further ANCOVA analysis revealed that rMSSD and SDNN were both significant (P<0.0001); however, only rMSSD exhibited a step-wise pattern of improvement when quartiles of rMSSD were compared to corresponding insulin reductions: Q1 (referent group, 8.41+/-3.2uIU/ml), Q2 (-3.30+/--3.2uIU/ml), Q3 (-5.66+/--3.2uIU/ml; P<0.02), and Q4 (-9.60+/--3.2uIU/ml; P<0.006).

CONCLUSION

Our study shows that changes in autonomic function are associated with changes in insulin and that exercise training may influence this relationship in postmenopausal women.

Effect of endurance training on blood pressure regulation, biomarkers and the heart in subjects at a higher age

We reported previously that two otherwise identical training programs at lower (LI) and higher intensity (HI) similarly reduced resting systolic blood pressure (BP) by approximately 4-6 mmHg. Here, we determined the effects of both programs on BP-regulating mechanisms, on biomarkers of systemic inflammation and prothrombotic state and on the heart. In this cross-over study (3 × 10 weeks), healthy participants exercised three times 1 h/week at, respectively, 33% and 66% of the heart rate (HR) reserve, in a random order, with a sedentary period in between. Measurements, performed at baseline and at the end of each period, involved blood sampling, HR variability, systolic BP variability (SBPV) and cardiac magnetic resonance imaging. Thirty-nine participants (18 men; mean age 59 years) completed the study. Responses were not different between both programs (P>0.05). Pooled data from LI and HI showed a reduction in HR (-4.3 ± 8.1%) and an increase in stroke volume (+11 ± 23.1%). No significant effect was seen on SBPV, plasma renin activity, basal nitric oxide and left ventricular mass. Our results suggest that the BP reduction observed appears to be due to a decrease in systemic vascular resistance; training intensity does not significantly affect the results on mechanisms, biomarkers and the heart.

The effect of aerobic training and cardiac autonomic regulation in young adults

OBJECTIVES

We tested the effect of aerobic exercise on autonomic regulation of the heart in healthy young adults.

METHODS

Healthy, sedentary young adults (n = 149; age = 30.4 +/- 7.53 years) were randomized to receive 12 weeks of either aerobic conditioning or strength training. Primary outcomes were heart rate and RR interval variability (RRV) measured before and after training and after 4 weeks of sedentary deconditioning. RRV, a noninvasive index of cardiac autonomic regulation, reflects variability in the intervals between consecutive R waves of the electrocardiogram.

RESULTS

Aerobic conditioning but not strength training led to a significant increase in aerobic capacity (3.11 mL/kg/min), a decrease in heart rate (-3.49 beats per minute), and an increase in high-frequency RRV (0.25 natural log msec2), each of which returned to pretraining levels after deconditioning. Significant 3-way interactions, however, revealed autonomic effects only in men.

CONCLUSIONS

In sedentary, healthy young adults, aerobic conditioning but not strength training enhances autonomic control of the heart, but post hoc analyses suggested that gender plays a significant role in this exercise-related cardioprotection.

Effects of low-intensity exercise conditioning on blood pressure, heart rate, and autonomic modulation of heart rate in men and women with hypertension

Untreated hypertension increases cardiovascular risk 2-fold to 3-fold, leading to serious cardiovascular problems that include left ventricular hypertrophy, stroke, ischemic heart disease, myocardial infarction, vascular disease, renal disease, and death. Exercise conditioning is recommended as one of the initial treatments for hypertension. The purpose of this pretest-posttest study was to quantify the effects of a 12-week home-based low-intensity exercise conditioning (walking) program in hypertensive men and women on systolic and diastolic blood pressure, heart rate, and autonomic modulation of heart rate. A total of 20 mildly hypertensive men and women who were assigned to a structured exercise (walking) program were compared with a control group of 20 nonexercising mildly hypertensive participants. Electrocardiographic heart rate and R-R interval data and beat-by-beat arterial blood pressure data were collected continuously for 10 min with participants in the supine and standing postures and during low-intensity steady-state exercise. The results show that systolic and diastolic blood pressure and R-R interval decreased and spontaneous baroreflex sensitivity increased in the exercise group. The decline in blood pressure was significant statistically and clinically. The increase in spontaneous baroreflex sensitivity indicates that the ability of the cardiovascular system to respond rapidly to changing stimuli improved after the 12-week walking protocol. The low-intensity exercise conditioning program achieved a training effect in this population.

Docosahexaenoic acid-rich fish oil improves heart rate variability and heart rate responses to exercise in overweight adults

Dietary fish oil supplementation and regular physical activity can improve outcomes in patients with established CVD. Exercise has been shown to improve heart rate variability (HRV), a predictor of cardiac death, but whether fish oil benefits HRV is controversial. Obese adults at risk of future coronary disease have impaired HRV and may benefit from these interventions. We evaluated the effect of DHA-rich tuna fish oil supplementation with and without regular exercise on HRV in sedentary, overweight adults with risk factors for coronary disease. In a randomised, double-blind, parallel comparison, sixty-five volunteers consumed 6 g fish oil/d (DHA 1·56 g/d, EPA 0·36 g/d) or sunflower-seed oil (placebo) for 12 weeks. Half of each oil group also undertook regular moderate physical activity (3 d/week for 45 min, at 75 % of age-predicted maximal heart rate (HR)). Resting HR and the HR response to submaximal exercise were measured at weeks 0, 6 and 12. In forty-six subjects, HRV was also assessed by power spectrum analysis of 20 min electrocardiogram recordings taken supine at baseline and 12 weeks. Fish oil supplementation improved HRV by increasing high-frequency power, representing parasympathetic activity, compared with placebo (P = 0·01; oil ×  time interaction). It also reduced HR at rest and during submaximal exercise (P = 0·008; oil ×  time interaction). There were no significant fish oil ×  exercise interactions. Dietary supplementation with DHA-rich fish oil reduced HR and modulated HRV in keeping with an improved parasympathetic–sympathetic balance in overweight adults with risk factors for future coronary disease.

Heart rate variability characteristics in sedentary postmenopausal women following six months of exercise training: the DREW study

BACKGROUND

Decreased heart rate variability (HRV) is associated with a higher risk of mortality. Overall, postmenopausal women have lower levels of HRV than premenopausal women, which may be additionally complicated by lifestyle related behaviors such as physical inactivity and obesity. Though cardiorespiratory exercise training increases HRV, little is known regarding the exercise dose necessary to promote this improvement.

METHODOLOGY/PRINCIPAL FINDINGS

Our primary aim was to measure HRV in post-menopausal women following 6-months of exercise training. We examined supine resting HRV in 373 post-menopausal women (45-75 y) after 6-months of randomly assigned and double-blinded administered exercise training exercise training at 50%, 100% and 150% of the NIH Consensus Development Panel's recommended minimal physical activity level. This corresponded to 4, 8, or 12 kcal/kg per week (KKW) of energy expenditure. At baseline, we observed no significant differences in HRV or hormone replacement use between treatment groups. However, we did observe that Caucasian women and those taking antidepressant medications had lower levels of baseline HRV. After 6-months of exercise intervention, we observed a dose dependent increase in all parasympathetically derived time and frequency domain measurements across exercise groups after adjustment for age, ethnicity, antidepressants, and baseline rMSSD (all, P<0.001). For example, the parasympathetic index rMSSD was greater than control (23.19+/-1.0) for the 4-KKW (25.98+/-0.8; P = 0.14), 8-KKW (27.66+/-1.0; P<0.05), and 12-KKW (27.40+/-0.0; P<0.05) groups at follow-up.

CONCLUSIONS/SIGNIFICANCE

Moderate intensity exercise training exercise is sufficient to improve HRV in previously sedentary postmenopausal women in a dose-dependent manner, as 4-KKW is insufficient to improve parasympathetic indices of HRV, while 12-KKW conferred no greater improvement than 8-KKW.

TRIAL REGISTRATION

Clinicaltrials.gov NCT 00011193.

Endurance training improves post-exercise cardiac autonomic modulation in obese women with and without type 2 diabetes

Obesity and type 2 diabetes (T2D) are associated with abnormal cardiovascular autonomic function and increased risk for cardiac complications, especially after exercise. Since improvements at rest are not always observed after training, we investigated changes in resting and post-exercise autonomic function in obese women with and without T2D after16-week of walking training. Heart rate (HR) variability (HRV) and baroreflex sensitivity (BRS) were measured at rest and 20 min after a 20 min bout of treadmill exercise at 65% VO(2) peak in obese women with (n = 8) and without T2D (n = 12) before and after training. HRV was analyzed by frequency-domain [high- (HF) power and low-frequency (LF)] and BRS by the sequence method. Exercise training induced similar significant changes in VO(2) peak, resting systolic blood pressure (SBP) and post-exercise autonomic function in both groups. Training increased VO(2 )peak (6%; P < 0.01) and decreased resting SBP (8%; P < 0.001). Increased post-exercise HR recovery (5%; P < 0.001), HF power (14%; P < 0.05), LF power (14%; P < 0.05) and BRS (86%; P < 0.001) were also observed. Resting autonomic function and post-exercise SBP were not altered after training. In conclusion, endurance training reduced blood pressure without changes in HRV and BRS at rest, but training increased HRV and BRS during the recovery of acute endurance exercise indicating an improved post-exercise autonomic modulation of HR, which was similar in obese women with and without T2D.

Low-dose exercise training does not influence cardiac autonomic control in healthy sedentary men aged 55-75 years

The purpose of this study was to evaluate the effects of a realistic, feasible, and commonly used fitness training programme on cardiac autonomic control in 14 sedentary men aged 62.0 +/- 6.1 years (mean +/- s). All participants performed a one-year fitness training programme in which training intensity and frequency were specifically chosen to be compliant for the majority of the participants (2-3 sessions per week at moderate intensity). At the same time, a reference group consisting of 15 sedentary age-matched men (age 64.2 +/- 6.5 years) did not change their habitual physical activity. Measurements were performed before and after the training intervention. Cardiac autonomic control was inferred from resting values (supine and standing) of heart rate variability (HRV) computed in the frequency domain over 10-min intervals. Endurance capacity was evaluated during a maximal incremental bicycle ergometer test. In spite of an increase in peak oxygen consumption (VO2peak) by 6.4% after training, heart rate in the training group remained unchanged at rest and at the same metabolic demand. No changes in resting parameters of HRV were shown for either groups or positions. Results from this study provide no evidence of a clinically meaningful increase in the vagal modulation to the sinus node at rest after one year of low-volume and moderate-intensity fitness training in men aged 55-75 years.

The use of heart rate variability measures to assess autonomic control during exercise

Heart rate variability (HRV) is a non-invasive indicator of cardiac autonomic modulation at rest. During rhythmic exercise, global HRV decreases as a function of exercise intensity. Measures reflecting sympathovagal interactions at rest do not behave as expected during exercise. This makes interpretation of HRV measures difficult, especially at higher exercise intensities. This problem is further confounded by the occurrence of non-neural oscillations in the high-frequency band due to increased respiratory effort. Alternative data treatments, such as coarse graining spectral analysis (CGSA), have demonstrated expected changes in autonomic function during exercise with some success. The separation of harmonic from fractal and/or chaotic components of HRV and study of the latter during exercise have provided further insight into cardioregulatory control. However, more research is needed. Some cross-sectional differences between HRV in athletes and controls during exercise are evident and data suggest longitudinal changes may be possible. Standard spectral HRV analysis should not be applied to exercise conditions. The use of CGSA and non-linear analyses show much promise in this area. Until further validation of these measures is carried out and clarification of the physiological meaning of such measures occurs, HRV data regarding altered autonomic control during exercise should be treated with caution.

Cardiovagal response to acute mild exercise in young healthy subjects

BACKGROUND

The aim of the present study was to investigate the effect of a single bout of mild exercise on autonomic nervous system activity in healthy subjects.

METHODS AND RESULTS

The study group comprised 18 healthy males, aged between 20 and 24 years, who had not been training regularly for the last 3 months. A supine recording of systolic arterial pressure (SAP) and RR interval and the administration of the phenylephrine test were performed at baseline and repeated after a 60-min recovery period following treadmill exercise training for 30 min at 65% of maximal heart rate. Mean SAP and RR interval, heart rate variability (HRV) indices (the standard deviation of normal-to-normal RR intervals (SDNN), the square root of the mean of squared differences between successive intervals and the percentage of adjacent RR intervals differing more than 50 ms), noninvasive spectral baroreflex sensitivity (Spe-BRS) and phenylephrine baroreflex sensitivity (Phe-BRS) were assessed before and after training. Mean SAP measured after exercise was lower than baseline (120+/-12 mmHg vs 128+/-12 mmHg, p = 0.05). Spe-BRS and Phe-BRS increased significantly after exercise, from 11.8+/-6.1 ms/mmHg to 16.0+/-7.8 ms/mmHg (p = 0.034), and from 16.0+/-8.8 ms/mmHg to 21.9+/-9.3 ms/mmHg (p = 0.022), respectively. A parallel increase was also observed in SDNN (from 81+/-44 ms to 96+/-53 ms, p = 0.02), but the other HRV indices showed no significant differences between pre- and post-exercise.

CONCLUSIONS

A single session of mild exercise performed by sedentary young men leads to significant autonomic nervous system improvement, which suggests that even mild physical activity is beneficial for neural cardiac regulation and should be recommended to sedentary healthy subjects.

Effects of Exercise on Heart Rate Variability: Inferences from Meta-Analysis

INTRODUCTION

Chronic exercise training produces a resting bradycardia that is thought to be due partly to enhanced vagal modulation.

PURPOSE

The aim of the present study was to determine the effects of exercise training on heart rate and measures of heart rate variability associated with vagal cardiac modulation and to quantify the relationship between changes in these measures.

METHODS

A random effects model of effect size (d) for change in high frequency (HF) power and RR interval was calculated. Within-group heterogeneity was assessed using the Q statistic. Where heterogenous effects were found, subgroup analyses were performed using the between-group Q statistic.

RESULTS

A meta-analysis of 13 studies measuring HF (N=322 cases) produced an overall effect size of d=0.48 (C.I. 0.26-0.70, P=0.00003). Twelve studies (298 cases) reported a change in RR interval with an overall effect size of d=0.75 (C.I. 0.51-0.96, P<0.00001). Effect sizes for RR interval data were significantly heterogenous. Subgroup analysis revealed significantly smaller responses of RR interval to training in older subjects (P<0.1). Effect sizes for change in HF were homogenous, although a trend toward an attenuated response to training was exhibited in older subjects (P>0.10). Linear, quadratic, and cubic fits all revealed weak (P>0.05) relationships between effect sizes for change in HF and RR interval.

DISCUSSION

Exercise training results in significant increases in RR interval and HF power. These changes are influenced by study population age. The smaller effect size for HF and weak relationship between HF and RR interval suggest factors additional to increased vagal modulation are responsible for training bradycardia.

Does the level of chronic physical activity alter heart rate variability in healthy older women?

In the present study, we investigated the effects of three levels of chronic physical activity on HRV (heart rate variability) in healthy older women. ECG recordings were taken in three (low-, moderate- and high-) activity groups in supine position with free and with controlled breathing, and during orthostatic stress. Temporal and spectral HRV indices were obtained from the ECG signal processing. The main results showed that, in supine position with free and controlled breathing, the HF (high-frequency) spectral component (P<0.01) and the rMSSD (square root of the mean squared differences) between two adjacent RR intervals (P<0.05 and P<0.01 respectively) were elevated in the high-activity group compared with the low-activity group. No significant difference was observed between groups during the orthostatic test. Within groups, in the supine position, the change from free to controlled breathing produced a decrease in the LF (low-frequency) spectral component in all three groups (P<0.01). The change from supine to standing position produced a decrease in RR in all three groups (P<0.05 in low- and moderate-activity groups, and P<0.01 in high-activity group); the rMSSD and the HF spectral component decreased only in the high-activity group (P<0.01). In conclusion, this study performed on older women showed that parasympathetic indices of resting HRV were significantly elevated in a high physical activity group compared with in a low physical activity group. Furthermore, parasympathetic indices of HRV decreased during an orthostatic test only in the high-activity group. The influence of chronic moderate physical activity on HRV in older women was small in the present study.

Eight weeks of moderate-intensity exercise training increases heart rate variability in sedentary postmenopausal women

BACKGROUND

Regular exercise is associated with increased heart rate variability (HRV). However, results from studies examining the effect of exercise training on HRV in postmenopausal women are inconclusive. In addition, the effect of hormone replacement therapy (HRT) on HRV remains a subject of speculation.

METHODS

We examined 88 sedentary postmenopausal women in a randomized controlled trial who were assigned to exercise (n = 49) or control (n = 39) groups. The exercising women performed 8 weeks of aerobic exercise training at a heart rate equivalent to 50% of VO2max, consisting on average of 44 minutes per session, 3 to 4 times per week. Resting HRV was measured in each participant at baseline and after 8 weeks of intervention. Ten minutes of resting R-R intervals were analyzed by time (standard deviation of mean R-R intervals, root of mean square successive differences) and frequency domain methods: low-frequency (LF) was defined as 0.04 to 0.15 Hz, high-frequency (HF) as 0.15 to 0.40 Hz, and total spectral power as 0.00 to 0.40 Hz. The LF and HF components in normalized units were also calculated.

RESULTS

At baseline, there were no significant differences in HRV between control and exercise groups. Additionally, there were no differences in any HRV variables when women were grouped by HRT use (no HRT, estrogen-only HRT, and progestin-containing HRT). After 8 weeks, women randomly assigned to the exercise group increased all absolute time and frequency domain indexes (all P <.001) and reduced resting heart rate (P =.002) compared with women in the control group. The LF and HF components expressed as normalized units remained unchanged after exercise intervention. Additionally, HRT use did not modify the exercise-induced changes in HRV.

CONCLUSIONS

We conclude that moderate aerobic exercise increases HRV in sedentary postmenopausal women. This benefit is not influenced by the use of HRT.

Heart rate variability in athletes

This review examines the influence on heart rate variability (HRV) indices in athletes from training status, different types of exercise training, sex and ageing, presented from both cross-sectional and longitudinal studies. The predictability of HRV in over-training, athletic condition and athletic performance is also included. Finally, some recommendations concerning the application of HRV methods in athletes are made.The cardiovascular system is mostly controlled by autonomic regulation through the activity of sympathetic and parasympathetic pathways of the autonomic nervous system. Analysis of HRV permits insight in this control mechanism. It can easily be determined from ECG recordings, resulting in time series (RR-intervals) that are usually analysed in time and frequency domains. As a first approach, it can be assumed that power in different frequency bands corresponds to activity of sympathetic (0.04-0.15 Hz) and parasympathetic (0.15-0.4 Hz) nerves. However, other mechanisms (and feedback loops) are also at work, especially in the low frequency band. During dynamic exercise, it is generally assumed that heart rate increases due to both a parasympathetic withdrawal and an augmented sympathetic activity. However, because some authors disagree with the former statement and the fact that during exercise there is also a technical problem related to the non-stationary signals, a critical look at interpretation of results is needed. It is strongly suggested that, when presenting reports on HRV studies related to exercise physiology in general or concerned with athletes, a detailed description should be provided on analysis methods, as well as concerning population, and training schedule, intensity and duration. Most studies concern relatively small numbers of study participants, diminishing the power of statistics. Therefore, multicentre studies would be preferable. In order to further develop this fascinating research field, we advocate prospective, randomised, controlled, long-term studies using validated measurement methods. Finally, there is a strong need for basic research on the nature of the control and regulating mechanism exerted by the autonomic nervous system on cardiovascular function in athletes, preferably with a multidisciplinary approach between cardiologists, exercise physiologists, pulmonary physiologists, coaches and biomedical engineers.

Effects of aerobic training on heart rate dynamics in sedentary subjects

This study was designed to assess the effects of moderate- and high-volume aerobic training on the time domain and on spectral and fractal heart rate (HR) variability indexes. Sedentary subjects were randomized into groups with moderate-volume training (n = 20), high-volume training (n = 20), and controls (n = 15). The training period was 8 wk, including 6 sessions/wk at an intensity of 70-80% of the maximum HR, lasting for 30 min/session in the moderate-volume group and 60 min/session in the high-volume group. Time domain, frequency domain, and short-term fractal scaling measures of HR variability were analyzed over a 24-h period. Mean HR decreased from 70 +/- 7 to 64 +/- 8 beats/min and from 67 +/- 5 to 60 +/- 6 beats/min (P < 0.001 for both) for the moderate- and high-volume training groups, respectively. The normalized high-frequency spectral component increased in both groups (P < 0.05). The normalized low-frequency component decreased significantly (P < 0.05), resulting in a marked decrease in low frequency-to-high frequency ratio in both groups. In addition, short-term scaling exponent decreased in both groups (P < 0.001). There were no significant differences in the changes of HR variability indexes between groups. Aerobic training in sedentary subjects results in altered autonomic regulation of HR toward vagal dominance. A moderate training volume is a sufficient intervention to induce these beneficial effects.

Cardiac autonomic nervous activities and cardiorespiratory fitness in older men

BACKGROUND

Aging associated changes in sympatho-vagal activities have been widely studied. However, little is known about the association between cardiorespiratory fitness level and cardiac autonomic nervous activities in conjunction with baroreflex sensitivity in healthy older men.

METHODS

We performed an incremental submaximal exercise test in 24 healthy, older men aged 60-70 years. They were divided into physically fit (PF, oxygen uptake at anaerobic threshold [ATO(2)] = 25.2 +/- 0.85 ml.kg(-1).min(-1)) and physically unfit (PU, ATO(2) = 19.6 +/- 0.42 ml.kg(-1).min(-1)) groups, based upon the results of an incremental exercise stress test. The cardiac autonomic nervous system (ANS) activities were assessed by means of power spectral analysis of heart rate variability. Baroreflex sensitivity (BRS) testing was performed using simultaneous beat-by-beat blood pressure and heart rate measurement during a transition from supine horizontal position to 60 degrees head-up-tilting (HUT).

RESULTS

At rest conditions, the high-frequency component ( p =.03) and total power ( p =.04) of heart rate variability spectrum were significantly higher in the PF group. The BRS assessed during passive HUT was also significantly higher (7.5 +/- 0.5 vs 3.0 +/- 0.4 ms.mm Hg(-1), p =.001) in the PF compared with the PU group. In addition, a significant correlation coefficient (r =.73, p =.001) was found between ATO(2) and BRS among the subjects.

CONCLUSIONS

The maintenance of high cardiorespiratory function, i.e., higher ATO(2) through a life-long active lifestyle including endurance exercise, may play an important role in reserving cardiac ANS and BRS in older men.

Biobehavioral approaches to the treatment of essential hypertension

Despite recent advances in the medical management of hypertension, chronically elevated blood pressure remains a major health problem in the United States, affecting almost 50 million Americans. It is widely recognized that lifestyle factors contribute to the development and maintenance of elevated blood pressure. This article critically reviews current approaches to the nonpharmacological treatment of high blood pressure and highlights outcome studies of exercise, weight loss and dietary modification, and stress management and relaxation therapies. Methodological issues in the assessment and treatment of hypertension are discussed, along with possible mechanisms by which lifestyle modification may reduce elevated blood pressure.

Mortality, cardiac vagal control and physical training--what's the link?

There is little doubt that regular exercise results in increases in life expectancy and protects against adverse cardiac events in both healthy subjects and patients with cardiovascular disease. The mechanism of action of physical training remains unclear but a variety of evidence points towards an enhancement in cardiac vagal activity protecting against lethal arrhythmias. Just how physical training increases cardiac vagal activity is an area that is ill understood but plausible mechanisms include mediation via angiotensin II or NO. Further research is needed in this area. Exercise training is demanding and difficult, particularly for patients with cardiac disease. If the mechanism of increase in cardiac vagal activity with training can be determined it may be possible to use pharmacological approaches to mimic the effects of exercise with potentially beneficial effects.

Exercise training and autonomic nervous system activity in obese individuals

PURPOSE

This study was designed to investigate the effects of 12 wk of exercise training on autonomic nervous system (ANS) in 18 obese middle-aged men (N = 9) and women (N = 9) (age: 41.6 +/- 1.2 yr; BMI: 27.3 +/- 0.4 kg x m(-2); %fat: 29.6 +/- 1.3%, mean +/- SE).

METHODS

Each subject participated in an aerobic exercise training at anaerobic threshold (AT), consisting of 30 min/session, 3 times/wk, for 12 consecutive weeks. The ANS activities were assessed by means of power spectral analysis of heart rate variability (HRV) at resting condition before, at 5 wk, and after the exercise program.

RESULTS

The exercise training resulted in a significant decrease in body mass, BMI, and % fat (P < 0.01) but not in lean body mass (P > 0.05) together with a significant increase in the AT VO2 (P < 0.01). Our power spectral data indicated that there were significant increases in the low-frequency component associated with the sympathovagal activity (0.03--0.15 Hz, 348.5 +/- 66.8 vs 694.7 +/- 91.5 ms(2), P < 0.01), the high-frequency vagal component (0.15--0.4 Hz, 146.3 +/- 30.4 vs 347.7 +/- 96.5 ms(2), P < 0.05), and the overall autonomic activity as evaluated by total power (0.03--0.4 Hz, 494.8 +/- 88.5 vs 1042.4 +/- 180.9 ms(2), P < 0.01) of HRV after the training.

CONCLUSIONS

Twelve weeks of exercise training has significantly improved both the sympathetic and parasympathetic nervous activities of the obese individuals with markedly reduced ANS activity, suggesting a possible reversal effect of human ANS functions. These favorable changes may also have an influence on the thermoregulatory control over the obesity.

Effects of increased physical activity and mild calorie restriction on heart rate variability in obese women

The effects of exercise and mild calorie restriction on heart rate variability (HRV) were investigated in 12 mildly obese, normotensive Japanese women aged 45.8+/-4.2 (SEM) years with a body mass index (BMI) of 27.3+/-0.4 kg/m2. The subjects participated in a 3-month program aimed at increasing physical activity and modifying eating behavior (intervention group). The control group consisted of 12 women (age 50.1+/-4.8 years, BMI 27.2+/-0.6 kg/m2) who did not attend the program. The frequency domain of HRV was calculated from 5-min Holter recordings while the subjects rested in a supine position. After 3 months, BMI decreased to 25.0+/-0.5 kg/m2 (p<0.001 vs baseline) in the intervention group, which was accompanied by decreases in body fat mass, waist circumference, serum total cholesterol and triglycerides, and improvement in insulin sensitivity. The mean and SD of the RR intervals, total power, and low and high frequency power of HRV significantly increased after the intervention, whereas no significant changes were seen for the controls. The changes in these HRV variables (calculated by subtracting the baseline values from the follow-up values) negatively correlated with the change in waist circumference, with the Pearson correlation coefficients being between -0.50 and -0.62 (p<0.05). A negative correlation was also seen between the changes in high frequency power and insulin resistance estimated by homeostasis model assessment (r=-0.49, p<0.05). The combination of exercise and mild calorie restriction led to changes in HRV indicative of an improvement in parasympathetic modulation.

Relative influence of age, resting heart rate and sedentary life style in short-term analysis of heart rate variability

In order to assess the relative influence of age, resting heart rate (HR) and sedentary life style, heart rate variability (HRV) was studied in two different groups. The young group (YG) consisted of 9 sedentary subjects aged 15 to 20 years (YG-S) and of 9 nonsedentary volunteers (YG-NS) also aged 15 to 20. The elderly sedentary group (ESG) consisted of 16 sedentary subjects aged 39 to 82 years. HRV was assessed using a short-term procedure (5 min). R-R variability was calculated in the time-domain by means of the root mean square successive differences. Frequency-domain HRV was evaluated by power spectrum analysis considering high frequency and low frequency bands. In the YG the effort tolerance was ranked in a bicycle stress test. HR was similar for both groups while ESG showed a reduced HRV compared with YG. Within each group, HRV displayed a negative correlation with HR. Although YG-NS had better effort tolerance than YG-S, their HR and HRV were not significantly different. We conclude that HRV is reduced with increasing HR or age, regardless of life style. The results obtained in our short-term study agree with others of longer duration by showing that age and HR are the main determinants of HRV. Our results do not support the idea that changes in HRV are related to regular physical activity.

Regular aerobic exercise modulates age-associated declines in cardiovagal baroreflex sensitivity in healthy men

1. Cardiovagal baroreflex sensitivity (BRS), the arterial baroreflex-mediated change in the R-R interval per unit change in systolic blood pressure, decreases with advancing age in sedentary adult humans. We determined the effects of regular aerobic exercise on the age-related decline in cardiovagal BRS. 2. In the cross-sectional study, 133 healthy men 18-79 years of age who were either sedentary, performing moderate aerobic exercise, or endurance exercise trained were studied. Among the sedentary men, cardiovagal BRS (phase IV of Valsalva's manoeuvre) was progressively lower (P < 0.05) in the middle-aged ( approximately 33 %) and older ( approximately 60 %) groups compared with the young group. In contrast, cardiovagal BRS was similar in the young and middle-aged men in the moderate exercise and endurance-trained groups. Cardiovagal BRS was lower (P < 0.05) in the older exercising men, but the magnitude of decline across age ( approximately 30 %) was only half as great as that in sedentary men. Cardiovagal BRS was 40-75 % greater (P < 0.05) in middle-aged and older men who exercised regularly compared with their sedentary peers. 3. In the intervention study, a 3 month aerobic exercise intervention (primarily walking) increased cardiovagal BRS by an average of 25 % (P < 0.05) in 13 previously sedentary middle-aged and older (56 +/- 1 years) healthy men. 4. Our results demonstrate for the first time that regular aerobic exercise: (1) attenuates the age-associated decline in cardiovagal BRS; and (2) partially restores the loss of cardiovagal BRS in previously sedentary middle-aged and older healthy men.

Controlled 5-mo aerobic training improves heart rate but not heart rate variability or baroreflex sensitivity

Endurance-trained athletes have increased heart rate variability (HRV), but it is not known whether exercise training improves the HRV and baroreflex sensitivity (BRS) in sedentary persons. We compared the effects of low- and high-intensity endurance training on resting heart rate, HRV, and BRS. The maximal oxygen uptake and endurance time increased significantly in the high-intensity group compared with the control group. Heart rate did not change significantly in the low-intensity group but decreased significantly in the high-intensity group (-6 beats/min, 95% confidence interval; -10 to -1 beats/min, exercise vs. control). No significant changes occurred in either the time or frequency domain measures of HRV or BRS in either of the exercise groups. Exercise training was not able to modify the cardiac vagal outflow in sedentary, middle-aged persons.

Heart rate variability in obese children: relations to total body and visceral adiposity, and changes with physical training and detraining

OBJECTIVE

Heart rate variability provides non-invasive information about cardiac parasympathetic activity (PSA). We determined in obese children: (1) relations of baseline PSA to body composition and hemodynamics; (2) effects of physical training (PT) and cessation of PT; and (3) which factors explained individual differences in responsivity of PSA to the PT.

RESEARCH METHODS AND PROCEDURES

The root mean square of successive differences (RMSSD) was the index of PSA. Obese children (n = 79) were randomly assigned to groups that participated in PT during the first or second 4-month periods of the study.

RESULTS

Baseline RMSSD was significantly (p<0.05) associated with lower levels of: fat mass, fat-free mass, subcutaneous abdominal adipose tissue, resting heart rate (HR), resting systolic blood pressure, and exercise HR. Stepwise multiple regression produced a final model (R2 = 0.36) that included only resting HR. The analysis of changes over the three time points of the study found a significant (p = 0.026) time by group interaction, such that RMSSD increased during periods of PT and decreased following cessation of PT. Greater individual increases in response to the PT (p<0.05) were seen in those who had lower pre-PT RMSSD levels, showed the greatest decreases in resting HR, and increased most in vigorous physical activity. The final regression model retained only the change in resting HR as a significant predictor of the changes in the RMSSD (R2 = 0.23).

DISCUSSION

Regular exercise that improved fitness and body composition had a favorable effect on PSA in obese children.

Aerobic exercise and resting blood pressure among women: a meta-analysis

PURPOSE

The aim of this study was to use the meta-analytic approach to examine the effects of aerobic exercise on resting systolic and diastolic blood pressure among adult women.

METHODS

Studies were retrieved from computer searches (MEDLINE, Sport Discus, Current Contents) and bibliographies of retrieved articles were cross-referenced. Inclusion criteria were as follows: (1) randomized trials, (2) aerobic activity as the primary exercise intervention, (3) comparative nonexercise control group included, (4) changes in resting systolic and/or diastolic blood pressure assessed for women ages 18 and older, and (5) studies published in English-language journals between January 1966 and January 1998. The primary outcomes retrieved in this study were changes in resting systolic and diastolic blood pressure calculated as the difference (exercise minus control) of the changes (initial minus final) in these mean values.

RESULTS

Ten studies representing 732 subjects and 36 primary outcomes (19 systolic, 17 diastolic) met the criteria for inclusion. Overall, an approximate 2% decrease in resting systolic and 1% decrease in resting diastolic blood pressure were observed (systolic,;x +/- SD = -2 +/- 2.6 mm Hg, 95% bootstrap confidence interval -3 to -1 mm Hg; diastolic,;x +/- SD = -1 +/- 1.9 mm Hg, 95% bootstrap confidence interval -2 to -1 mm Hg).

CONCLUSION

Aerobic exercise results in small reductions in resting systolic and diastolic blood pressure among adult women. However, a need exists for additional, well-designed studies on this topic, especially among hypertensive adult women.