Heart rate variability and cardiovascular fitness in senior athletes

Uncertainties in the Analysis of Heart Rate Variability: A Systematic Review

Heart rate variability (HRV) is an important metric with a variety of applications in clinical situations such as cardiovascular diseases, diabetes mellitus, and mental health. HRV data can be potentially obtained from electrocardiography and photoplethysmography signals, then computational techniques such as signal filtering and data segmentation are used to process the sampled data for calculating HRV measures. However, uncertainties arising from data acquisition, computational models, and physiological factors can lead to degraded signal quality and affect HRV analysis. Therefore, it is crucial to address these uncertainties and develop advanced models for HRV analysis. Although several reviews of HRV analysis exist, they primarily focus on clinical applications, trends in HRV methods, or specific aspects of uncertainties such as measurement noise. This paper provides a comprehensive review of uncertainties in HRV analysis, quantifies their impacts, and outlines potential solutions. To the best of our knowledge, this is the first study that presents a holistic review of uncertainties in HRV methods and quantifies their impacts on HRV measures from an engineer's perspective. This review is essential for developing robust and reliable models, and could serve as a valuable future reference in the field, particularly for dealing with uncertainties in HRV analysis.

A New Approach for Evaluation of Cardiovascular Fitness and Cardiac Responses to Maximal Exercise Test in Master Runners: A Cross-Sectional Study

The aim of this study was to analyze the cardiac autonomic function at rest, at maximum exercise, and in recovery after exercise and to determine sex-specific and age-specific values for resting heart rate (RHR), hear rate (HR)-peak, HR recovery (HRR), and HR variability at rest in master runners. Fifty endurance runners (21 women) participated in this study (43.28 ± 5.25 years). The subjects came from different athletic clubs in Andalusia (Spain), and the testing protocol was performed in-season. A 3-km running test was performed and the cardiovascular response was monitored. Regarding sex, no significant differences were found regarding cardiovascular autonomic function at rest, during exercise, and following maximal exercise, only at rest, the standard deviation of all R-R intervals and low frequency values displayed significantly (p < 0.05) lower scores in women. 46% of athletes showed an RHR < 60 bpm. Additionally, HR-peak showed a significant correlation with age (r = −0.369; p = 0.009) and HRR5min (r = 0.476, p = 0.001). Also, endurance performance was inversely associated with obesity traits and cardiometabolic risk factors. In summary, age, sex, fitness, or anthropometrics characteristics did not show a relevant influence on cardiovascular autonomic modulation in master runners. However, the 3-km performance displayed a significant negative association with several factors of cardiometabolic risk.

The association between heart rate behavior and gait performance: The moderating effect of frailty

Introduction

Research suggests that frailty not only influence individual systems, but also it affects the interconnection between them. However, no study exists to show how the interplay between cardiovascular and motor performance is compromised with frailty.

Aim

To investigate the effect of frailty on the association between heart rate (HR) dynamics and gait performance.

Methods

Eighty-five older adults (≥65 years and able to walk 9.14 meters) were recruited (October 2016—March 2018) and categorized into 26 non-frail (age = 78.65±7.46 years) and 59 pre-frail/frail individuals (age = 81.01±8.17) based on the Fried frailty phenotype. Participants performed gait tasks while equipped with a wearable electrocardiogram (ECG) sensor attached to the chest, as well as wearable gyroscopes for gait assessment. HR dynamic parameters were extracted, including time to peak HR and percentage increase in HR in response to walking. Using the gyroscope sensors gait parameters were recorded including stride length, stride velocity, mean swing velocity, and double support.

Results

Among the pre-frail/frail group, time to peak HR was significantly correlated with all gait parameters (p<0.0001, r = 0.51–0.59); however, for the non-frail group, none of the correlations between HR dynamics and gait performance parameters were significant (p>0.45, r = 0.03–0.15). The moderation analysis of time to peak HR, demonstrated a significant interaction effect of HR dynamics and frailty status on walking velocity (p<0.01), and the interaction effect was marginally non-significant for other gait parameters (p>0.10).

Conclusions

Current findings, for the first time, suggest that a compromised motor and cardiac autonomic interaction exist among pre-frail/frail older adults; an impaired HR performance (i.e., slower increase of HR in response to stressors) may lead to a slower walking performance. Assessing physical performance and its corresponding HR behavior should be studied as a tool for frailty screening and providing insights about the underlying cardiovascular-related mechanism leading to physical frailty.

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

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.

Effects of different exercise interventions on heart rate variability and cardiovascular health factors in older adults: a systematic review

Background

Aging impairs physiological processes in the autonomic nervous, endocrine, and cardiovascular systems which are associated with increased risk of cardiovascular disease. Heart rate variability (HRV), the beat-to-beat variations of successive heartbeats, is an indicator of cardiac autonomic control and cardiovascular health. Physical activity has beneficial effects on cardiovascular health. However, no review has been conducted to summarize the effects of different exercise modalities on HRV in older adults. Therefore, the aim of this systematic review was to summarize the effects of endurance, resistance, coordinative, and multimodal exercise interventions on resting HRV and secondary health factors in healthy older adults aged 60 years in average and over.

Methods

Five databases (PubMed, Scopus, SPORTDiscus, Ovid, and Cochrane Library) were searched for eligible studies published between 2005 and September 8th, 2020. Two reviewers independently assessed the studies for potential inclusion. Outcome measures were changes in resting HRV indices, baroreflex sensitivity, blood pressure, body fat, body mass, body mass index, cardiac output, distance in the six-minute walking test, stroke volume, total peripheral resistance, and VO₂ max or VO₂ peak from pre to post intervention. The methodological quality of the final data set was assessed using two scales (TESTEX and STARD_HRV). This review was registered in PROSPERO: CRD42020206606.

Results

The literature search retrieved 3991 articles, of which 13 were included in the review. Five studies used multimodal, three studies endurance, two studies resistance, two studies coordinative, and one study used an endurance and a resistance training intervention. The majority of the studies revealed significant positive effects on cardiac autonomic control, except for the resistance training interventions. All exercise modalities improved secondary health factors. The methodological quality assessment revealed a few criteria to improve the quality of and comparability between studies.

Conclusion

This systematic review revealed beneficial effects on cardiac autonomic control in healthy older adults through endurance, coordinative, and multimodal training but not through resistance training. Secondary health factors improved after all types of physical interventions. Future investigations should more thoroughly adhere to methodological standards of exercise interventions and ECG recording for the assessment of autonomic regulation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11556-021-00278-6.

Low ventilatory responsiveness to transient hypoxia or breath-holding predicts fast marathon performance in healthy middle-aged and older men

The aim of this study was to test the utility of haemodynamic and autonomic variables (e.g. peripheral chemoreflex sensitivity [PCheS], blood pressure variability [BPV]) for the prediction of individual performance (marathon time and VO_2max) in older men. The post-competition vasodilation and sympathetic vasomotor tone predict the marathon performance in younger men, but their prognostic relevance in older men remains unknown. The peripheral chemoreflex restrains exercise-induced vasodilation via sympathetically-mediated mechanism, what makes it a plausible candidate for the individual performance marker. 23 men aged ≥ 50 year competing in the Wroclaw Marathon underwent an evaluation of: resting haemodynamic parameters, PCheS with two methods: transient hypoxia and breath-holding test (BHT), cardiac barosensitivity, heart rate variability (HRV) and BPV, plasma renin and aldosterone, VO_2max in a cardiopulmonary exercise test (CPET). All tests were conducted twice: before and after the race, except for transient hypoxia and CPET which were performed once, before the race. Fast marathon performance and high VO_2max were correlated with: low ventilatory responsiveness to hypoxia (r =  - 0.53, r = 0.67, respectively) and pre-race BHT (r =  - 0.47, r = 0.51, respectively), (1) greater SD of beat-to-beat SBP (all p < 0.05). Fast performance was related with an enhanced pre-race vascular response to BHT (r =  - 0.59, p = 0.005). The variables found by other studies to predict the marathon performance in younger men: post-competition vasodilation, sympathetic vasomotor tone (LF-BPV) and HRV were not associated with the individual performance in our population. The results suggest that PCheS (ventilatory response) predicts individual performance (marathon time and VO_2max) in men aged ≥ 50 yeat. Although cause-effect relationship including the role of peripheral chemoreceptors in restraining the post-competition vasodilation via the sympathetic vasoconstrictor outflow may be hypothesized to underline these findings, the lack of correlation between individual performance and both, the post-competition vasodilation and the sympathetic vasomotor tone argues against such explanation. Vascular responsiveness to breath-holding appears to be of certain value for predicting individual performance in this population, however.

Heart Rate Variability Mainly Relates to Cognitive Executive Functions and Improves Through Exergame Training in Older Adults: A Secondary Analysis of a 6-Month Randomized Controlled Trial

Heart rate variability (HRV) mirrors autonomic nervous system activities and might serve as a parameter to monitor health status in older adults. However, it is currently unknown which functional health measures, including cognitive, physical, and gait performance parameters, are most strongly related to HRV indices. This knowledge would enable implementing HRV assessments into health monitoring routines and training planning for older adults. Simultaneous cognitive-motor and exergame training may be effective to improve HRV indices but has not been investigated yet. Eighty-nine healthy older adults (≥70 years of age) were randomized into three groups: (1) virtual reality video game dancing, i.e., exergaming (DANCE); (2) treadmill walking with simultaneous verbal memory training (MEMORY); or (3) treadmill walking only (PHYS). Strength and balance exercises complemented each program. Over 6 months, two weekly 1-h training sessions were performed. HRV indices (standard deviation of N-N intervals, SDNN; root mean square of successive R-R interval differences, RMSSD; and absolute power of high-frequency band (0.15-0.4 Hz), HF power) and various measures of cognitive, physical, and gait performance were assessed at baseline and after 3 months and 6 months. Multiple linear regression analyses with planned comparisons were calculated. At baseline, 8-12% of HRV variance was significantly explained by cognitive executive functions and leg strength (inversely related). Verbal long-term memory, aerobic and functional fitness, and gait performance did not contribute to the model (SDNN: R² = 0.082, p = 0.016; RMSSD: R² = 0.121, p = 0.013; HF power: R² = 0.119, p = 0.015). After 6 months, DANCE improved HRV indices, while MEMORY and PHYS did not (time × intervention interactions: first-contrast DANCE/MEMORY vs. PHYS: SDNN p = 0.014 one-tailed, ΔR ² = 0.020 and RMSSD p = 0.052 one-tailed (trend), ΔR ² = 0.007; second-contrast DANCE vs. MEMORY: SDNN p = 0.002 one-tailed, ΔR ² = 0.035, RMSSD p = 0.017 one-tailed, ΔR ² = 0.012, and HF power p = 0.011 one-tailed, ΔR ² = 0.013). We conclude that mainly cognitive executive functions are associated with HRV indices and that exergame training improves global and parasympathetic autonomic nervous system activities in older adults. Periodic assessments of HRV in older citizens could be particularly beneficial to monitor cognitive health and provide indications for preventative exercise measures.

Heart rate variability in middle-aged sprint and endurance athletes

BACKGROUND

Aging is associated with decreased autonomic balance which could be assessed by Heart Rate Variability (HRV). Exercise training improves autonomic balance, but there is a lack in the literature regarding the heart rate variability (HRV) of master sprinters and endurance athletes.

PURPOSE

The effects of lifelong endurance and sprint training on cardiac autonomic balance were assessed in master athletes and compared with age-matched controls and young untrained controls.

METHODS

Participants (n = 81) were 8 master sprinters (MS; 51.8 ± 11.1 yrs), 8 master endurance athletes (EN, n = 8, 53.6 ± 8.6 yrs), 17 age-matched untrained (CON, 47.47 ± 6.00 yrs) and 48 young controls (YC, 25.40 ± 3.87 yrs). For the acquisition of RR intervals (iRR) (Polar RS800X Heart Rate Monitor®) the participants remained seated for 15-min with the final 10-min being considered for analysis. HRV was measured using Kubios software. A one-way ANOVA with repeated measures was applied.

RESULTS

All studied parameters did not differ between MS and EN {Time Domain [HR (bpm) 59.00 ± 6.13 vs. 58.94 ± 12.75], [R-R (ms) 1030.45 ± 107.45 vs. 1068.77 ± 206.17], [SDNN (ms) 57.35 ± 20.07 vs. 80.66 ± 71.07], [RMSSD (ms) 40.88 ± 20.07 vs. 38.93 ± 20.44]; Non-linear domain [SD1 (ms) 28.93 ± 14.20 vs. 27.56 ± 14.46]}, whose demonstrated a reduced HR and elevated mean R-R intervals in comparison to both YC {[HR (bpm) 69.64 ± 9.81]; [R-R (ms) 883.93 ± 124.11]} and age-matched controls {[HR (bpm) 70.06 ± 6.63]; [R-R (ms) 865.11 ± 78.39]}. It was observed a lower HRV for middle-aged CON {[RMSSD (ms) 20.23 ± 5.87], [SDNN (ms) 37.79 ± 10.15] and [SD1 (ms) 14.31 ± 4.15]} compared to YC {[RMSSD (ms) 43.33 ± 26.41], [SDNN (ms) 67.07 ± 28.77] and [SD1 (ms) 30.66 ± 18.69; p < .05]}. These last age-related differences were not observed for MS and EN.

CONCLUSION

For master athletes, regardless of whether they are trained in endurance or sprinters, both training modes revealed to be equally beneficial in attenuating the effects of aging on the autonomic balance.

Cross-sectional associations between physical activity and selected coronary heart disease risk factors in young adults. The Cardiovascular Risk in Young Finns Study

OBJECTIVE

Physical activity (PA) may reduce the risk of coronary heart disease (CHD) by inducing beneficial changes in several risk factors. We studied the associations between PA and a range of risk markers of CHD in young adults.

METHODS AND RESULTS

We measured serum lipoproteins, oxidized LDL, adipokines, inflammatory markers, metabolic markers, and arginine metabolites in 2,268 individuals (age 24-39 y). Participants were asked frequency, duration, and intensity of PA in leisure time. In addition, commuting to work was assessed. In both sexes, PA was inversely associated with waist circumference (all P < 0.0001). After controlling for sex, age, and waist circumference, PA was directly associated with HDL-cholesterol and apolipoprotein A1, and inversely with heart rate, smoking, oxidized LDL, apolipoprotein B, insulin, glucose, C-reactive protein, leptin, L-arginine, and phospholipase A2 activity (all P < 0.05).

CONCLUSION

These population-based data are consistent with the idea that the beneficial effects of PA on CHD risk are mediated by favorable influences on several risk factors, as judged by independent relations to markers of lipoprotein metabolism, glucose metabolism, and inflammation. These associations reflect beneficial effects on cardiovascular health in both sexes and may offer mechanistic insights for the inverse association between PA and CHD.

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.

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.

Heart rate variability in myocardial infarction and heart failure

The need to refine the identification of patients who might benefit from implantation of an implantable cardioverter defibrillator has been risen by the results of many clinical trials on ICD therapy. Traditional parameters such as left ventricular ejection fraction and the presence of non-sustained ventricular tachycardia were not strong enough to achieve this goal with reasonable cost-effectiveness. Heart rate variability (HRV) is one of the most popular parameters used to assess the autonomic tone. HRV has been reported as a strong predictor of cardiovascular mortality. Currently, three different categories of methods in HRV analysis are being used; the time domain, frequency domain, and non-linear dynamic analysis. Both time domain and frequency domain analyses of HRV have been investigated extensively regarding their use as a prognostic marker for cardiovascular mortality. The non-linear dynamic analysis is the latest tool that has shown to have an even higher predictive value than any of the traditional parameters. However, standardized and supporting evidence on this new technique is still lacking. In this article, the current role of HRV in the prediction of cardiovascular mortality in myocardial infarction and heart failure patients has been reviewed.

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 many metrics of cardiac chronotropy: a pragmatic primer and a brief comparison of metrics

This paper focuses on pragmatic issues in obtaining measures of cardiac vagal control, and overviews a set of freely available software tools for obtaining several widely used metrics that putatively reflect sympathetic and/or parasympathetic contributions to cardiac chronotropy. After an overview of those metrics, and a discussion of potential confounds and extraneous influences, an empirical examination of the relationships amongst these metrics is provided. This study examined 10 metrics in 96 unselected college students under conditions of resting baseline and serial paced arithmetic. Intercorrelations between metrics were very high. Factor analyses were conducted on the metrics reflecting variability in cardiac rate, once at baseline and again during mental arithmetic. Factor structure was highly stable across tasks, and included a factor that had high loadings of all variables except Toichi's "cardiac sympathetic index" (CSI), and a second factor that was defined predominantly by the CSI. Although generally highly correlated, the various metrics responded differently under challenge.

Vagal modulation and aging

Cardiovascular disease accounts for approximately 30% of all deaths worldwide, and will only worsen as the world's population ages. It is well-established that age, per se, is a major risk factor and contributor to all cardiovascular morbidities and mortalities. However, environmental factors, including a lack of exercise, appear to play a critical role in the onset and progression of cardiovascular disease. This paper reviews the literature on cardiac variability and aging and addresses risk factors associated with aging that can be modified and possibly attenuate the decline of heart rate variability with aging, including exercise training to increase vagal modulation. Thus, results of the studies described in this review support a potential benefit of increasing or maintaining fitness in order to slow the decline of parasympathetic control of HR with normal aging.

Regular physical exercise, heart rate variability and turbulence in a 6-year randomized controlled trial in middle-aged men: The DNASCO study

HRV and HRT are independent predictors of cardiovascular mortality. Aging reduces HRV, but results from the physical exercise trials are controversial. The primary aim was to study changes in heart rate variability (HRV) and heart rate turbulence (HRT) in a six-year controlled randomized trial at regular low to moderate intensity physical exercise. One hundred forty men aged 53--63 years were randomized in to an exercise or a control groups. The participants underwent a maximal bicycle ergometer exercise test with respiratory gas analyses annually for six years. At baseline and after intervention, 24-h ambulatory ECG registrations were performed to assess HRV (n=100). HRT was determined among subjects with single ventricular premature complexes (VPC) (n=73). In the exercise group, ventilatory aerobic threshold (VAT) increased by 16% indicating enhanced submaximal cardiorespiratory fitness. No significant differences were found in any of the HRV or HRT parameters between the groups. However, the observed increase in VAT correlated significantly with the improvement in HRV parameters. The change in turbulence slope (TS) correlated with the changes in most HRV variables and the change in turbulence onset (TO) correlated with the changes in three frequency domain parameters. Our results suggest that in addition to improvement in submaximal cardiorespiratory fitness, regular low to moderate intensity physical exercise seems to have beneficial effects also on cardiac autonomic nervous function, a clinically relevant predictor of cardiovascular morbidity and mortality.

Heart Rate Variability and Intensity of Habitual Physical Activity in Middle-Aged Persons

PURPOSE

In the middle-aged, it has been shown that moderate physical activity is associated with increased global HR variability (HRV) and vagal-related HRV indexes. However, the relative effect of quantity and intensity of physical activity on HRV is still unknown. The purpose of this study was to compare HRV indexes in three groups of subjects presenting different long-term physical activity profiles: sedentary subjects (SED) with low-energy expenditure (PAEE) and two groups of subjects with equivalent moderate PAEE, but differing in terms of intensity of physical activity (active (ACT) and sportive (SP) individuals).

METHODS

Forty-three middle-aged subjects (61.2 +/- 4.3 yr) were divided into the three groups on the basis of a physical activity questionnaire (Modified Baecke Questionnaire for Older Adults). Physical activity was evaluated by accelerometry for 1 wk. Time and frequency domain HRV indexes were determined during quiet periods in the morning on 5-min stationary R-R interval segments under controlled breathing. Quality of life was evaluated using the SF-36 Health Survey Questionnaire.

RESULTS

SP spent more time in moderate to very high activities than ACT (2.1 +/- 0.1 vs 0.6 +/- 0.1 h.wk(-1); P < 0.05) and less time in very light to light activities (62.8 +/- 2.0 vs 73.7 +/- 1.7 h.wk(-1); P < 0.05). SP presented higher vagal-related HRV indexes than SED (P < 0.05), whereas increases in ACT were less marked. ACT and SP had similar health status scores, which were higher than for SED (P < 0.05).

CONCLUSIONS

In older adults with different lifestyles, habitual moderate PAEE is associated with better self-estimated overall health status and higher vagal-related HRV indexes compared with subjects with low PAEE, especially when moderate- to very high-intensity physical activities are undertaken.

A longitudinal study of physical activity and heart rate recovery: CARDIA, 1987-1993

PURPOSE

Autonomic nervous system function may be a mechanism by which frequent physical activity is associated with better coronary heart disease outcomes. In a diverse, population-based sample, we tested whether physical activity participation was associated with higher parasympathetic function.

METHODS

Participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study underwent symptom-limited graded exercise testing at baseline (1985-1986; N=3446) and at 7 yr follow-up (N=1627). Heart rate recovery (HRR), the difference between maximum heart rate (HR) and HR 2 min after test cessation, was used to estimate parasympathetic activity.

RESULTS

Participants who self-reported in the highest tertile of total physical activity (the sum of moderate- and heavy-intensity activities) had significantly faster HRR than participants in the lowest tertile (45.1 vs 41.8 beats.min, P<0.01), and the odds of having abnormal HRR (<or=22 beats.min) were 1.9 (95% confidence interval: 1.1, 3.4) times greater in the lowest versus the highest tertile after adjustment for age, race, gender, body mass index, smoking status, and diastolic blood pressure. Findings were consistent across strata of covariates. On average, HRR declined 2.5 beats.min over 7 yr. HRR declined the least among participants whose physical activity increased (-1.3 beats.min) or remained stable (-1.8 beats.min), compared with participants whose physical activity decreased (-3.6 beats.min; P<0.01 vs increase or stable).

CONCLUSIONS

In this diverse, population-based sample, physical activity was associated with faster HRR from an exercise treadmill test. Regular physical activity may blunt age-related declines in autonomic nervous system function.

The Bicycle Makes the Eyes Smile: Exercise, Aging, and Psychophysical Well-Being in Older Italian Cyclists

Despite a cultural and biomedical consensus about the health benefits of physical activity, most adults do not exercise regularly and their activity tends to decline further in older age. This study reports on a group of older-age Italian bicyclists who maintain extraordinary activity levels. It explores the physical and mental health effects of intensive exercise in older people, the meanings and motivations associated with it, and the cultural and social features that support and promote bicycling in Italy. The findings suggest some public health implications for the prevention of chronic diseases caused by inactivity and excessive body weight.

Heart rate variability in sportive elderly: relationship with daily physical activity

PURPOSE

Aging is associated with decreased heart rate variability (HRV). As aerobic training is known to increase HRV, the purpose of this study was to evaluate the influence of long-term lifestyle on HRV in very old adults with regard to their usual physical activity.

METHODS

Twenty-four older adults (mean 75.7 +/- 0.2 yr) were divided into two groups according to their sport activities assessed by the Modified Baecke Questionnaire for Older Adults. Sedentary subjects (SED) were compared to elderly regularly involved in sport activities (SP). The subjects were supine for 20 min and the last 5 min were used to determine HR and HRV indexes as the standard deviation of normal intervals (SDNN), the root-mean-square differences of successive normal R-R intervals (RMSSD), and the high-frequency (HF) and low-frequency (LF) power. Physical activity was evaluated during 1 wk by triaxial accelerometry and analyzed in terms of intensity and duration.

RESULTS

Daily physical activity energy expenditure given by the accelerometer was significantly higher in SP than in SED (P < 0.05). SP spent more time per week in activity of intensity higher than 3 resting metabolic equivalents (METs), but total activity time was significantly higher for SED than for SP (P < 0.05). SP showed significantly (P < 0.05) lower resting heart rate than SED, higher global HRV (SDNN), and higher parasympathetic-related HRV indexes (RMSSD, HF, and HF/(LF+HF)) (P < 0.05).

CONCLUSIONS

Our results indicate that in very old subjects a long-term sportive lifestyle, which increases total daily energy expenditure and physical activity intensity, is associated with higher global HRV and vagal-related indexes and thus may counteract the age-related decline in cardiac autonomic control better than a sedentary lifestyle.

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.

Enhanced cardiac vagal efferent activity does not explain training-induced bradycardia

Studies of heart rate variability (HRV) have so far produced contradictory evidence to support the common belief that endurance training enhances cardiac parasympathetic tone. This may be related to the fact that most studies failed to specifically isolate the vagally mediated influence of respiration. This study used a cross-sectional comparison of endurance athletes (n=20; ATHL) exhibiting resting bradycardia and age-matched nonathletes (n=12; CRTL) to indirectly assess training effects on amplitude and timing characteristics of respiratory sinus arrhythmia (RSA). Continuous electrocardiogram (ECG) and ventilatory flows were recorded during spontaneous breathing (SP), as well as during breathing at four cycles less than (M4) or more (P4) than SP, to also examine potential repercussions of training on the sensitivity of the cardiac vagal responses to breathing. A fast Fourier transform procedure was used to quantify the standard spectral high-frequency (HF) and low-frequency (LF) components and a respiratory-centered frequency (RCF) component of HRV. RSA was assessed using a breath-by-breath quantification of the amplitude and timing of the maximum change in instantaneous heart rate. Under baseline SP conditions, heart rate was lower in ATHL (62.6+/-6.5 vs. 75.2+/-9 beats/min; p<0.05) while blood pressure (BP), breath cycle duration, tidal volume, and ventilatory drive were similar in both groups. HRV total spectral power density, LF, HF, or RCF was not different between groups at either the SP, M4, or P4 conditions. Changes in total breath duration similarly affected RSA amplitude in all groups, while HR and BP remained unchanged from SP. RSA phase was not affected by training status or by changes in total breath duration. RSA amplitude was negatively related to breathing frequency in all groups (p<0.05), while the mean slope of the relationship (sensitivity) was not different between groups. In as much as RSA is an adequate marker of cardiac vagal efferent activity, these results add support to a contribution of a decrease in intrinsic heart rate to explain training-induced bradycardia.

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.

Heart rate monitoring: applications and limitations

Over the last 20 years, heart rate monitors (HRMs) have become a widely used training aid for a variety of sports. The development of new HRMs has also evolved rapidly during the last two decades. In addition to heart rate (HR) responses to exercise, research has recently focused more on heart rate variability (HRV). Increased HRV has been associated with lower mortality rate and is affected by both age and sex. During graded exercise, the majority of studies show that HRV decreases progressively up to moderate intensities, after which it stabilises. There is abundant evidence from cross-sectional studies that trained individuals have higher HRV than untrained individuals. The results from longitudinal studies are equivocal, with some showing increased HRV after training but an equal number of studies showing no differences. The duration of the training programmes might be one of the factors responsible for the versatility of the results.HRMs are mainly used to determine the exercise intensity of a training session or race. Compared with other indications of exercise intensity, HR is easy to monitor, is relatively cheap and can be used in most situations. In addition, HR and HRV could potentially play a role in the prevention and detection of overtraining. The effects of overreaching on submaximal HR are controversial, with some studies showing decreased rates and others no difference. Maximal HR appears to be decreased in almost all 'overreaching' studies. So far, only few studies have investigated HRV changes after a period of intensified training and no firm conclusions can be drawn from these results. The relationship between HR and oxygen uptake (VO(2)) has been used to predict maximal oxygen uptake (VO(2max)). This method relies upon several assumptions and it has been shown that the results can deviate up to 20% from the true value. The HR-VO(2) relationship is also used to estimate energy expenditure during field conditions. There appears to be general consensus that this method provides a satisfactory estimate of energy expenditure on a group level, but is not very accurate for individual estimations. The relationship between HR and other parameters used to predict and monitor an individual's training status can be influenced by numerous factors. There appears to be a small day-to-day variability in HR and a steady increase during exercise has been observed in most studies. Furthermore, factors such as dehydration and ambient temperature can have a profound effect on the HR-VO(2) relationship.

Assessment of autonomic function in high level athletes by pupillometry

Spectral analysis of heart rate variability has become a noninvasive standard method for assessment of autonomic nervous system activity in athletes. The effect of exercise training on autonomic regulation of pupillary light reflex is not known. The purpose of this study was to evaluate pupil autonomic function in athletes. We studied 46 highly trained athletes practicing gymnastics, swimming, long-distance running, soccer, and 51 healthy control subjects, using a portable infrared pupillometry. Five left pupil light response curves were recorded for each subject; the 485 pupillogram records were processed by a computer system. The following pupillometric parameters calculated were significantly higher (P<0.05) in runners than in controls: reflex amplitude (2.1 mm; 95% CI, 1.9-2.3 vs. 1.8 mm; 95% CI, 1.7-1.9), mean percent reflex amplitude of initial diameter (34%; 95% CI, 32-37 vs. 30%, 95% CI, 28-31) and mean time at which pupil redilated 75% of reflex amplitude (2.15 s; 95% CI, 1.99-2.31 vs. 1.86 s; 95% CI, 1.78-1.93). Sex, age, height, weight, body mass index and years of sports practice had no significant influence in the evaluated parameters. The results were consistent with an increased parasympathetic activity and a reduced sympathetic activity of pupillary light reflex in endurance-trained runners, supporting the hypothesis of a generalized "dysautonomy" associated with this type of training.

Cardiac sympathetic dysfunction in an athlete's heart detected by 123I-metaiodobenzylguanidine scintigraphy

The athlete's heart is commonly characterized by an increase in left ventricular mass because of an increase in the left ventricular diastolic cavity dimensions or wall thickness or both. Endurance exercise also induces numerous cardiovascular adaptations, including increased vagal tone. However, the sympathetic function has not yet been precisely elucidated, so the present study evaluated cardiac sympathetic nerve function from metaiodobenzylguanidine (MIBG) images obtained 15 and 180 min after the injection of 123I-MIBG at a dose of 111 MBq. The ratio of heart/mediastinum count (H/M) and the washout rates of 123I-MIBG (WR) were calculated in 25 consecutive patients who were athletes (aged 52+/-13 years) and 23 normal subjects. There was a significant difference in the H/M between the athletic and normal hearts (2.3+/-0.3 vs 2.6+/-0.3, p<0.01, Scheffe's test). An increased WR was observed in the athletes group when compared with the normal group (34+/-4 vs 28+/-3, p<0.01), and there was a significant correlation between WR and the left ventricular mass index (r=0.578, p<0.01). Prolonged exercise training may alter cardiac sympathetic nerve function, which can be detected by MIBG imaging.

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.

Autonomic mechanisms and sudden death after abrupt coronary occlusion

In spite of recent advances in secondary prevention, sudden cardiac death has remained a major public health problem as the majority of fatalities occur in subjects without a history of severe heart disease. Abrupt rupture of a vulnerable plaque resulting in thrombotic occlusion of a coronary artery is a common cause of sudden death in this population. Coronary occlusion does not, however, invariably lead to sudden death but may cause acute myocardial infarction or exacerbation of chest pain. Extensive studies in experimental animals and increasing clinical evidence indicate that autonomic nervous activity has a significant role in modifying the clinical outcome. Sympathetic hyperactivity favours the genesis of life-threatening ventricular tachyarrhythmias while vagal activation exerts an antifibrillatory effect. Strong afferent stimuli from the ischaemic myocardium impair arterial baroreflex and may lead to dangerous haemodynamic instability. Studies with a human angioplasty model have shown that there is wide interindividual variation in the type and severity of autonomic reactions during the early phase of abrupt coronary occlusion, a critical period for out-of-hospital cardiac arrest. The site of the occlusion is not a significant determinant of the reactions, whereas the severity of a coronary stenosis, adaptation or ischaemic preconditioning, beta-blockade and gender seem to affect the autonomic reactions and occurrence of complex ventricular arrhythmias. Clinical and angiographic factors are, however, poor predictors of autonomic reactions in an individual patient. Recent studies have documented a hereditary component for autonomic function, and genetic factors may also modify the clinical manifestations of acute coronary occlusion.