Influence of age and moderate-intensity exercise training on heart rate variability in young and mature adults

Effect of exercise training on heart rate variability in type 2 diabetes mellitus patients: A systematic review and meta-analysis

Background

Cardiac autonomic neuropathy is a common complication of type 2 diabetes mellitus (T2DM), that can be measured through heart rate variability (HRV)–known to be decreased in T2DM. Physical exercise can improve HRV in healthy population, however results are under debate in T2DM. We conducted a systemic review and meta-analysis to assess the effects of physical exercise on HRV in T2DM patients.

Method

PubMed, Cochrane, Embase, and ScienceDirect databases were searched for all studies reporting HRV parameters in T2DM patients before and after exercise training, until September 20th 2020, without limitation to specific years. We conducted random-effects meta-analysis stratified by type of exercise for each of the HRV parameters: RR–intervals (or Normal to Normal intervals–NN), standard deviation of RR intervals (SDNN), percentage of adjacent NN intervals varying by more than 50 milliseconds (pNN50), root mean square of successive RR-intervals differences (RMSSD), total power, Low Frequency (LF), High Frequency (HF) and LF/HF ratio. Sensitivity analyses were computed on studies with the highest quality.

Results

We included 21 studies (9 were randomized) for a total of 523 T2DM patients: 472 had an exercise training and 151 were controls (no exercise). Intervention was endurance (14 studies), resistance (2 studies), endurance combined with resistance (4 studies), and high intensity interval training (HIIT) (4 studies). After exercise training, all HRV parameters improved i.e. an increase in SDNN (effect size = 0.59, 95%CI 0.26 to 0.93), RMSSD (0.62, 0.28 to 0.95), pNN50 (0.62, 0.23 to 1.00), HF (0.58, -0.16 to 0.99), and a decrease in LF (-0.37, -0.69 to -0.05) and LF/HF (-0.52, -0.79 to -0.24). There were no changes in controls. Stratification by type of exercise showed an improvement in most HRV parameters (SDNN, RMSSD, pNN50, LF, HF, LF/HF) after endurance training, whereas mostly LF/HF was improved after both resistance training and HIIT. Supervised training improved most HRV parameters. Duration and frequency of training did not influence the benefits on HRV.

Conclusion

Exercise training improved HRV parameters in T2DM patients which may reflect an improvement in the activity of the autonomic nervous system. The level of proof is the highest for endurance training. Supervised training seemed beneficial.

Sex-Specific Autonomic Responses to Acute Resistance Exercise

Background and Objectives: Acute resistance exercise (RE) reduces vagal modulation and increases sympathovagal balance, which increases the risk for arrythmias. Few studies have examined sex differences in autonomic modulation after acute RE. The purpose of this investigation was to examine sex-specific responses to acute RE on autonomic modulation. Materials and Methods: Twenty-one resistance-trained individuals (men n = 11, women n = 10) between the ages of 19 and 25 y were analyzed for autonomic modulation in response to acute RE and a control (CON). Measures of autonomic modulation were collected at rest, 15 (R15), and 30 (R30) min following both conditions. Heart rate (HR), log transformed root mean square of successive differences (lnRMSSD), total power (lnTP), low-frequency power (lnLF), high-frequency power (lnHF), sample entropy (SampEn), and Lempel-Ziv entropy (LZEn) were measured at all time points. A three-way repeated analysis of variance (ANOVA) was used to analyze sex (men, women) across condition (RE, CON) and time (Rest, R15, R30). Results: The results are similar for all heart rate variability (HRV) variables at rest for both conditions (RE, CON). SampEn was significantly higher in men compared to women at rest for both conditions (p = 0.03), with no differences in LZEn (p > 0.05). There were no significant (p > 0.05) three-way interactions on any variables. Condition by time interactions demonstrated that both sexes increase in HR (p = 0.0001) and lnLF/HF ratio (p = 0.001), but decreases in lnRMSSD (p = 0.0001), lnTP (p < 0.0001), lnLF (p < 0.0001), lnHF (p = 0.0001), and LZEn (p = 0.009) at R15 and R30 compared to rest following acute RE and were different from CON. Condition by time interaction (p = 0.017) demonstrated that SampEn was attenuated at R15 compared to rest, and the CON, but not R30 following acute RE. Conclusion: Although SampEn is more complex at rest in men compared to women, autonomic modulation responses between sexes following acute RE appear to be similar.

Heart Rate Variability and Physical Demands of In-Season Youth Elite Soccer Players

Monitoring fatigue and performance is important for adjusting training loads in soccer. Therefore, knowing the status of the player when applying a training stimulus is key to optimizing the players' development. This study aims to evaluate the interaction between internal and external load, during training and matches, in an elite youth soccer team.

METHODS

seventeen youth players of the highest Spanish category were monitored with GPS devices during training and matches, as well as recording their nocturnal heart rate variability (HRV). We employed a linear mixed model to assess the physical demands between training and matches, and to compare the HRV variables.

RESULTS

a higher total distance (+2993.35-5746.56 m; ES = 1.4), distance at high intensity (+641.24-1907 m; ES = 1.5), sprint distance (+350.46-795.05 m; ES = 2.1), number of sprints (+18.38-41.58; ES = 1.9), and number of repeated sprints (+5.91-15.30; ES = 1.7) (all p < 0.001), but not in the number of accelerations, were reported during the matches when compared to the training sessions during the 11 weeks. The analysis of the HRV variables showed no significant differences between the accumulated values during a training week, providing similar results pre-match or post-match (p > 0.05). The LF/HF_RATIO showed a negative influence on the total distance ran, distance at high intensity, distance in sprint, number of sprints, and repeated sprint. RR_MEAN was positively related to the sprint number.

CONCLUSION

the results of the present study suggest that nocturnal HRV variables are not different between pre-match and post-match. Furthermore, it suggests that LF/HF_RATIO and RR_MEAN during pre-match can determine the external load that the player will be able to complete during the match.

The moderating effect of heart rate variability on the relationship between alpha asymmetry and depressive symptoms

Electroencephalographic (EEG) research has suggested relatively reduced brain activity in the left frontal and right posterior region trait-markers of depression. However, inconsistent results have been reported. Based on previous studies reporting the heart rate variability (HRV) as an index of emotional regulation, this study makes a novel investigation of the role of heart rate variability (HRV) as a moderator in the relationship between frontal and parietal alpha asymmetry and depression. Resting EEG (eyes open) was recorded in 38 patients with MDD and 34 healthy subjects. Frontal and parietal alpha asymmetries were calculated at total (8–12 Hz), high (10–12 Hz), and low (8–10 Hz) alpha frequency bands. Three vagally mediated HRV (vmHRV) components (LF, HF, and the LF/HF ratio) were calculated in the frequency domain. Relatively greater right parietal alpha activity significantly predicted the severity of depression only when HF was low (or the LF/HF ratio was high) at low alpha frequency band. The interaction effect of parietal alpha asymmetry and vmHRV remained significant after including anxiety score as a covariate. No moderation effect of vmHRV was found for frontal sites and other frequency bands, as well as healthy subjects. These findings suggest that vmHRV moderates the association between parietal alpha asymmetry at low frequency band and depression for MDD patients. We suggest that the interaction between parietal alpha asymmetry and vmHRV may be a biomarker of MDD.

The effects of yoga and quiet rest on subjective levels of anxiety and physiological correlates: a 2-way crossover randomized trial

Background

Rest or acute exercise can decrease state anxiety, with some evidence showing exercise to prevent laboratory-induced elevations in anxiety. No study has examined whether yoga provides short-term protection against laboratory-induced anxiety. The aim of this study was to examine the effectiveness of an acute YogaFit session on state anxiety and measures of heart rate variability (HRV) to determine whether yoga provides short-term protection against emotional picture stimuli.

Methods

A randomized repeated-measures crossover clinical trial was performed. Forty healthy, female college students completed a 30 min session of YogaFit and a time-matched seated rest condition on separate days. After each condition, participants viewed 30 min of emotional picture stimuli. State anxiety, heart rate and time-domain and frequency-domain measures of HRV were assessed baseline, post- condition, and post-exposure to emotional stimuli. Data were analysed using a condition x time (2 × 3) repeated-measures ANOVA.

Results

Post-hoc comparisons indicate the following: (1) state anxiety significantly decreased from baseline to post-condition for both yoga and rest (p = 0.001) but returned to baseline values following exposure to emotional stimuli (p < 0.001) for both conditions; (2) heart rate decreased post-condition to post-exposure (p = 0.020) and baseline to post-exposure (p = 0.033) for both conditions; (3) time-domain measure of HRV showed a significant increase in HRV between baseline and post-condition (p = 0 .019), post-condition and post-exposure (p = 0 .007), and between baseline and post-exposure (p < 0.001).

Conclusions

Both YogaFit and seated rest were effective at acutely reducing state anxiety post-condition, but not at preventing an induced anxiety response post-exposure. Following exposure to the emotionally stimulating pictures, there was a shift from the high frequency-domain to the low frequency-domain and an increase in the time-domain measure of HRV for both the YogaFit and the quiet rest condition.

Trial registration

Retrospectively registered 2/16/2018, clinicaltrials.gov, Identifier: NCT03458702.

Electronic supplementary material

The online version of this article (10.1186/s12906-018-2343-1) contains supplementary material, which is available to authorized users.

The Effects of High-Intensity Interval Training vs. Moderate-Intensity Continuous Training on Heart Rate Variability in Physically Inactive Adults

Physically inactive adults are prevalent worldwide. This study compared the effects of short-term high-intensity interval training (HIIT) versus moderate-intensity continuous training (MICT) on heart rate variability (HRV) in physically inactive adults as a preliminary study. Thirteen physically inactive male adults (27.5 ± 3.80 years) were randomly assigned to HIIT (N = 7) or MICT (N = 6). The HIIT program consisted of 20 min of interval training with cycling to rest ratio of 10/50 s at ≥90% HR_peak, while the MICT program consisted of 40 min of continuous cycling at 60–75% HR_peak. Both groups completed eight sessions of training within two weeks. Time and frequency domains of HRV were measured for 20 min with Actiwave-Cardio monitor (CamNtech, UK). The number of R-R interval and inter-beat interval (IBI) were significantly improved (p < 0.05) in both HIIT and MICT programs following eight sessions of training. A significant interaction effect for group by time was found in the lnLF/HF ratio (p < 0.05) where it was only improved in the HIIT group from pre- to post-test. The HIIT program is superior to MICT in improving HRV in physically inactive adults. The HIIT program can be applied as a time-efficient program for improving cardiac-autoregulation.

Age alters cardiac autonomic modulations during and following exercise-induced heat stress in females

The aim of this study was to examine the effect of natural ageing on heart rate variability during and following exercise-induced heat stress in females. Eleven young (∼24 years) and 13 older (∼51 years), habitually active females completed an experimental session consisting of baseline rest, moderate intensity intermittent exercise (four 15-min bouts separated by 15-min recovery) and 1-hour of final recovery in a hot and dry (35°C, 20% relative humidity) environment. Respiratory and heart rate recordings were continuously logged with 10-min periods analysed at the end of: baseline rest; each of the exercise and recovery bouts; and during the 1-hour final recovery period. Comparisons over time during exercise and recovery, and between groups were conducted via two-way repeated-measures ANCOVAs with rest values as the covariate. During baseline rest, older females exhibited lower heart rate variability compared to young females with similar levels of respiration and most (∼71-79%) heart rate variability measures during repeated exercise and recovery. However, older females exhibited heart rate variability metrics suggestive of greater parasympathetic modulation (greater long axis of Poincare plot, cardiac vagal index; lower low-high frequency ratio) during repeated exercise with lower indices during the latter stage of prolonged recovery (less very low frequency component, Largest Lyapunov Exponent; greater cardiac sympathetic index). The current study documented several unique, age-dependent differences in heart rate variability, independent of respiration, during and following exercise-induced heat stress for females that may assist in the detection of normal heat-induced adaptations as well as individuals vulnerable to heat stress.

Vigorous physical activity predicts higher heart rate variability among younger adults

BACKGROUND

Baseline heart rate variability (HRV) is linked to prospective cardiovascular health. We tested intensity and duration of weekly physical activity as predictors of heart rate variability in young adults. Time and frequency domain indices of HRV were calculated based on 5-min resting electrocardiograms collected from 82 undergraduate students. Hours per week of both moderate and vigorous activity were estimated using the International Physical Activity Questionnaire. In regression analyses, hours of vigorous physical activity, but not moderate activity, significantly predicted greater time domain and frequency domain indices of heart rate variability. Adjusted for weekly frequency, greater daily duration of vigorous activity failed to predict HRV indices.

CONCLUSIONS

Future studies should test direct measurements of vigorous activity patterns as predictors of autonomic function in young adulthood.

Does Concurrent Training Intensity Distribution Matter?

Varela-Sanz, A, Tuimil, JL, Abreu, L, and Boullosa, DA. Does concurrent training intensity distribution matter? J Strength Cond Res 31(1): 181-195, 2017-Previous research has demonstrated the influence of intensity distribution on endurance training adaptations. However, no study has addressed the influence of intensity distribution on the effectiveness of concurrent training (CT). The main objective of this study was to compare the effects of 2 CT programs with different training intensity distribution and externally equated loads on physical fitness. Thirty-one sport science students volunteered and were evaluated for resting heart rate variability (HRV), countermovement jump, bench press, half squat, and maximum aerobic speed (MAS). All were randomly distributed into either a traditional-based training group (TT; n = 11; 65-75% of MAS, combined with 10-12 repetition maximum [RM]), polarized training group (PT; n = 10; 35-40% and 120% of MAS, combined with 5RM and 15RM), or control group (CG; n = 10). After 8 weeks of training (3 daysweek), TT and PT exhibited similar improvements in MAS, bench press, and half squat performances. No differences were observed between TT and PT groups for perceived loads. There were no changes in HRV for any group, although TT exhibited a reduction in resting heart rate. Compared with other groups, the PT group maintained jump capacity with an increment in body mass and body mass index without changes in body fatness. In conclusion, PT induced similar improvements in physical fitness of physically active individuals when compared with TT. However, PT produced a lower interference for jumping capacity despite an increment in body mass, whereas TT induced greater bradycardia. Extended studies with different intensity distributions should be conducted to better determine the dose-response of CT in various populations.

Autonomic cardiac regulation, blood pressure and cardiorespiratory fitness responses to different training doses over a 12 week group program in the elderly

AIM

The study assessed the effects of different weekly training frequencies performed over a 12 week exercise programme (strength, endurance, balance) on autonomic cardiac activity, blood pressure and cardiorespiratory fitness (CRF) in elderly individuals.

METHODS

Fifty-eight individuals participated in the study: 2TG (N=24, 71.1±6.4 yrs; 19 females, 5 males) performing two, 60min sessions/week; and 3TG (N=34, 72.3±7.9 yrs; 25 females, 9 males) performing three, 60min sessions/week. Time domain and spectral analysis of heart rate variability (HRV) quantified autonomic cardiac regulation.

RESULTS

Natural logarithm (Ln) transformation was applied to all HRV parameters. There were significant reductions in total power (Ln TP) (p=0.006), low frequency (Ln LF) (p=0.013), high frequency (Ln HF) (p=0.013) and root mean square of successive differences (Ln rMSSD) (p=0.014) post training in 3TG after intervention. Diastolic BP (DBP) decreased significantly in both groups (2TG: P<0.001; 3TG: P<0.001). Both groups showed significant improvements in six-minute walk distance (2TG: P=0.003, 3TG: P=0.001). However, there were significant HRV differences between 2TG and 3TG for Ln TP (P=0.018), Ln LF (P=0.049), Ln HF (P=0.039) and Ln rMSSD (P=0.049).

CONCLUSIONS

A combined exercise programme resulted in improved DBP and CRF irrespective of training two or three 60min sessions/week. However, training three, sessions/week induced negative health-related changes in autonomic cardiac activity through reducing HRV parasympathetic function, while HRV was maintained in the group training twice a week.

Effect of chronic training on heart rate variability, salivary IgA and salivary alpha-amylase in elite swimmers with a disability

The purpose of this study was to a) determine the heart rate variability (HRV) and saliva markers of immunity (salivary immunoglobulin A; sIgA) and stress (salivary alpha-amylase; sAA) responses to chronic training in elite swimmers with a disability; and b) identify the relationships between HRV, sIgA, sAA and training volume. Eight members of a high performance Paralympic swimming program were monitored for their weekly resting HRV, sIgA and sAA levels in the 14 weeks leading up to a major international competition. The 14 week training program included aerobic, anaerobic, power and speed, and taper training phases, while also incorporating two swimming step tests and two swimming competitions. Specific time (root mean square of the successive differences; RMSSD) and frequency (high frequency normalized units [HFnu]) domain measures, along with non-linear indices (standard deviation of instantaneous RR variability; SD1 and short term fractal scaling exponent; α1) of HRV were used for all analyses with effects examined using magnitude-based inferences. Relationships between HRV and saliva markers were identified by Spearman rank rho (ρ) correlation coefficients. Compared with week 1, SD1 was very likely lower (96/4/0, ES = -2.21), while sAA was very likely elevated (100/0/0, ES = 2.32) at the beginning of week 7 for all athletes. The training program did not alter HRV or saliva whereas competition did. There were also no apparent differences observed for HRV, sIgA and sAA between each of the training phases during the 14 week swimming program. Correlations were observed between sAA and SD1 (ρ = -0.212, p<0.05), along with sAA and mean HR (ρ = 0.309, p<0.05). These results show that high level national competition influences depresses HRV (SD1) and increases saliva biomarkers of stress (sAA). It appears that a well-managed and periodised swimming program can maintain these indices within normal baseline levels. The study also highlighted the parasympathetic nervous system influence on sAA.

Heart rate variability stabilization in athletes: towards more convenient data acquisition

Resting heart rate variability (HRV) is a potentially useful marker to consider for monitoring training status in athletes. However, traditional HRV data collection methodology requires a 5-min recording period preceded by a 5-min stabilization period. This lengthy process may limit HRV monitoring in the field due to time constraints and high compliance demands of athletes. Investigation into more practical methodology for HRV data acquisitions is required. The aim of this study was to determine the time course for stabilization of ECG-derived lnRMSSD from traditional HRV recordings. Ten-minute supine ECG measures were obtained in ten male and ten female collegiate cross-country athletes. The first 5 min for each ECG was separately analysed in successive 1-min intervals as follows: minutes 0-1 (lnRMSSD0-1 ), 1-2 (lnRMSSD1-2 ), 2-3 (lnRMSSD2-3 ), 3-4 (lnRMSSD3-4 ) and 4-5 (lnRMSSD4-5 ). Each 1-min lnRMSSD segment was then sequentially compared to lnRMSSD of the 5- to 10-min ECG segment, which was considered the criterion (lnRMSSDC riterion ). There were no significant differences between each 1-min lnRMSSD segment and lnRMSSDC riterion , and the effect sizes were considered trivial (ES ranged from 0·07 to 0·12). In addition, the ICC for each 1-min segment compared to the criterion was near perfect (ICC values ranged from 0·92 to 0·97). The limits of agreement between the prerecording values and lnRMSSDC riterion ranged from ±0·28 to ±0·45 ms. These results lend support to shorter, more convenient ECG recording procedures for lnRMSSD assessment in athletes by reducing the prerecording stabilization period to 1 min.

Differential cardiac effects of aerobic interval training versus moderate continuous training in a patient with schizophrenia: a case report

Increased cardiovascular morbidity and mortality rates for patients with schizophrenia are reported to contribute to their reduced life expectancy. Common reasons for increased cardiac mortality rates include cigarette smoking, obesity, dyslipidemia, diabetes, and poorer health behavior in general. The majority of excess mortality among people with schizophrenia is caused by cardiovascular complications. Reduced vagal activity might be one important mechanism leading to this increased cardiac mortality and has been consistently described in patients and their healthy first-degree relatives. In this case study, we compared two different aerobic exercise regimes in one patient with chronic schizophrenia to investigate their effects on cardiovascular regulation. The patient completed a 6-week period of moderate continuous training (CT) followed by a 6-week period of interval training (IT), each regime two times per week, on a stationary bicycle. This was followed by a 6-week period of detraining. Primary outcome measures examined heart rate (HR) and heart rate variability (HRV) at rest while secondary measures assessed fitness parameters such as the ventilatory threshold 1 (VT1). We observed that IT was far more effective than moderate CT in increasing HRV, as indicated by root mean of squared successive difference (improvement to baseline 27 versus 18%), and reducing resting HR (-14 versus 0%). Improvement in VT1 (21 versus -1%) was only observed after IT. Our study provides preliminary data that the type of intervention is highly influential for improving cardiac function in patients with schizophrenia. While cardiovascular function might be influenced by CT to some degree, no such effect was present in this patient with schizophrenia. In addition, the beneficial effect of IT on HR regulation vanished completely after a very short period of detraining after the intervention.

Autonomic correlates of Yo-Yo performance in soccer referees

We tested the hypothesis that: basal cardiac autonomic modulation (i.e. heart rate variability, HRV) was associated with the parasympathetic withdrawal during, and overall Yo-Yo IR1 performance; and therefore HRV could be used as a simple tool for specific fitness assessment. Nine sub-elite soccer referees performed the Yo-Yo IR1 until exhaustion with simultaneous recording of heart rate with the autonomic response during exercise calculated as the area under the curve (AUC). In the same week but with at least 48 hrs between days, a night-time HR recording was obtained from participants for determination of basal HRV. Correlation analysis demonstrated strong (r>0.83) relationships among Yo-Yo IR1 performance, AUC and basal HRV. These results indicate that both nocturnal HRV and AUC can be utilised as simple and valid monitoring tools of soccer referees' fitness.

Endothelial nitric oxide synthase polymorphisms and adaptation of parasympathetic modulation to exercise training

PURPOSE

There is a large interindividual variation in the parasympathetic adaptation induced by aerobic exercise training, which may be partially attributed to genetic polymorphisms. Therefore, we investigated the association among three polymorphisms in the endothelial nitric oxide gene (-786T>C, 4b4a, and 894G>T), analyzed individually and as haplotypes, and the parasympathetic adaptation induced by exercise training.

METHODS

Eighty healthy males, age 20-35 yr, were genotyped by polymerase chain reaction-restriction fragment length polymorphism analysis, and haplotypes were inferred using the software PHASE 2.1. Autonomic modulation (i.e., HR variability and spontaneous baroreflex sensitivity) and peak oxygen consumption (VO(2peak)) were measured before and after training (running, moderate to severe intensity, three times per week, 60 min·day(-1), during 18 wk).

RESULTS

Training increased VO(2peak) (P < 0.05) and decreased mean arterial pressure (P < 0.05) in the whole sample. Subjects with the -786C polymorphic allele had a significant reduction in baroreflex sensitivity after training (change: wild type (-786TT) = 2% ± 89% vs polymorphic (-786TC/CC) = -28% ± 60%, median ± quartile range, P = 0.03), and parasympathetic modulation was marginally reduced in subjects with the 894T polymorphic allele (change: wild type (894GG) = 8% ± 67% vs polymorphic (894GT/TT) = -18% ± 59%, median ± quartile range, P = 0.06). Furthermore, parasympathetic modulation percent change was different between the haplotypes containing wild-type alleles (-786T/4b/894G) and polymorphic alleles at positions -786 and 894 (-786C/4b/894T) (-6% ± 56% vs -41% ± 50%, median ± quartile range, P = 0.04).

CONCLUSIONS

The polymorphic allele at position -786 and the haplotype containing polymorphic alleles at positions -786 and 894 in the endothelial nitric oxide gene were associated with decreased parasympathetic modulation after exercise training.

[Heart rate variability analysis in sports]

Differences in the duration of the cycles reflects the balance of the sympathetic and parasympathetic influence on the heart. Variance in the heart rate correlates to the breathing cycle, to baroreflex sensitivity, to day and night alternations and to changes in the vegetative tone evoked by physical exercises. Analysis of the time and/or frequency power domain of the heart rate variance is expected to have diagnostic value in physiological and pathological situations as adaptation to training, overtraining, heart disease etc. Both time- and frequency domains reflect the same physiological phenomenon but from different point of view. Vagus tonus is reflected in the high frequency part of the range of variance, while an increased sympathetic tone enriches the low frequency part of the variations of the duration of the consecutive heart cycles. This technically simple and relatively inexpensive method has inspired a couple of clinical and sports medical studies. Certain tendencies seem to be clear, but for individual diagnosis or for prognosis the data must be treated very carefully.

Levels of agreement for RR intervals and short-term heart rate variability obtained from the Polar S810 and an alternative system

The aim of this study was to assess the agreement between HRV measures derived from a time series of RR intervals recorded by a standard 12-lead ECG (CP) and a commercially available RR interval recorder (S810). Thirty-three participants (19 males) (median age 36, range 20-63) underwent simultaneous, 5-min, supine RR-interval recordings. Each RR interval time series was analysed using the software supplied with the recording equipment. Two comparisons were then made. First, a comparison of RR interval data recording and editing only was made. Second, comparisons were made for measures of HRV derived from edited RR interval data. Agreement between RR intervals and standard HRV measures were assessed using intraclass correlation coefficient and limits of agreement. Agreement of HRV measures derived from RR intervals recorded and edited by individual systems was not acceptable. Agreement analyses for the number of RR intervals recorded and edited by each systems software showed excellent intraclass correlation coefficients (ICC lower 95% CI > 0.75) and acceptably narrow limits of agreement (LoA). These data indicate that the number of RR intervals recorded by S810 can agree well those recorded from a standard 12-lead ECG. This is true even after application of system specific data editing procedures. Commercial RR-interval recorders may offer a simple, inexpensive alternative to full 12-lead ECG in the recording and editing of RR intervals for subsequent HRV analysis in healthy populations.

Cardiac vagal outflow after aerobic training by analysis of high-frequency oscillation of the R–R interval

This study was designed to assess the effect of aerobic training on the dynamics between the R-R interval length and the high-frequency (HF) oscillation of the R-R interval. Seventeen healthy males (26+/-2 years) participated in an 8-week aerobic training intervention. The mean HF spectral power (0.15-0.4 Hz) of the R-R interval and the mean R-R interval length were analyzed from 24-h recordings. HF power was also analyzed in 5-min sequences and plotted as a function of the corresponding mean R-R interval length. The relationship between the R-R interval length and the HF power was analyzed by a quadratic regression model. The relationship was defined as saturated if the distinct deflection point of the model occurred before the maximum R-R interval. Otherwise, the relationship was defined as linear. Additionally, the mean HF power was calculated from the linear portion of the R-R interval versus the HF power regression curve (HF index). Before the training intervention, seven subjects had a saturated HF power. After the intervention, five new cases of saturated HF power were observed. The mean HF power of the 24-h recording did not change in the group with a saturated HF power before training (7.4+/-0.8 vs. 7.6+/-0.8 ms(2)), but the HF index increased (6.7+/-0.7 vs. 7.1+/-0.7 ms(2), P<0.05). We conclude that enhanced vagal activity due to aerobic training increases the prevalence of the saturation of the HF oscillation of the R-R interval variability in healthy subjects. HF power calculated from unsaturated area detects more accurately subtle changes in the vagally mediated beat-to-beat variability of the R-R interval after aerobic training than the mean 24-h HF power.

The reliability of short-term measurements of heart rate variability

Short-term assessment of heart rate variability (HRV) is a non-invasive technique to examine ANS function. Within the literature, HRV is commonly referred to as a reliable measurement technique. The aim of this review was to assess the accuracy of this description based upon a comprehensive review of the available data concerning reliability of short-term HRV measures. Reviewing only studies using appropriate statistical analyses, it was determined that reliability coefficients for HRV measures were highly varied. Coefficients of variation ranged from <1% to >100%. Similar variation was found in studies using the intraclass correlation coefficient values, and limits of agreement. Reliability coefficients reported displayed some distinct patterns. Firstly, where measurements were made during interventions such as tilt or pharmacological stimulation, reliability was poorer than when HRV was measured at rest. Secondly, clinical populations displayed poorer reliability than healthy subjects. There was little effect of test-retest duration on reliability and although no single HRV measurement appeared less reliable than another, there was evidence that optimal data collection conditions for specific frequency domain measures exist. Describing HRV as a reliable measurement technique appears to be a gross oversimplification, as results of reliability studies are heterogeneous, and dependent on a number of factors. Further studies are required, particularly in clinical populations to assess HRV reliability. Authors should refer to coefficients from similar populations measured under similar conditions when making future sample size calculations.

Effects of age and physical activity on the autonomic control of heart rate in healthy men

The effects of the aging process and an active life-style on the autonomic control of heart rate (HR) were investigated in nine young sedentary (YS, 23 +/- 2.4 years), 16 young active (YA, 22 +/- 2.1 years), 8 older sedentary (OS, 63 +/- 2.4 years) and 8 older active (OA, 61 +/- 1.1 years) healthy men. Electrocardiogram was continuously recorded for 15 min at rest and for 4 min in the deep breathing test, with a breath rate of 5 to 6 cycles/min in the supine position. Resting HR and RR intervals were analyzed by time (RMSSD index) and frequency domain methods. The power spectral components are reported in normalized units (nu) at low (LF) and high (HF) frequency, and as the LF/HF ratio. The deep breathing test was analyzed by the respiratory sinus arrhythmia indices: expiration/inspiration ratio (E/I) and inspiration-expiration difference (deltaIE). The active groups had lower HR and higher RMSSD index than the sedentary groups (life-style condition: sedentary vs active, P < 0.05). The older groups showed lower HFnu, higher LFnu and higher LF/HF ratio than the young groups (aging effect: young vs older, P < 0.05). The OS group had a lower E/I ratio (1.16) and deltaIE (9.7 bpm) than the other groups studied (YS: 1.38, 22.4 bpm; YA: 1.40, 21.3 bpm; OA: 1.38, 18.5 bpm). The interaction between aging and life-style effects had a P < 0.05. These results suggest that aging reduces HR variability. However, regular physical activity positively affects vagal activity on the heart and consequently attenuates the effects of aging in the autonomic control of HR.

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.

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.

Agreement between three commercially available instruments for measuring short-term heart rate variability

Numerous instruments are commercially available to measure heart rate variability, yet little is known regarding the agreement between such instruments. The objective of this study is to assess agreement between measures of heart rate variability in three commercially available instruments. Thirty subjects (20 males) of median age 27.5 (range 19-59 years) underwent simultaneous ECG recordings, under three different resting conditions: supine, standing and supine with controlled breathing, using three commercially available analysers. Intraclass correlation coefficients tended to show excellent agreement (lower 95% C.I., R > 0.75) between all instruments under all conditions. However, further analysis of selected measurements using the limits of agreement method revealed large variation in values generated by all instruments. There was also an evidence of systematic bias between one instrument and the remaining two. The latter finding was due to discrepant ECG recording protocols that were unrelated to consistent operator timing. This study demonstrates that measures of HRV generated by the three instruments did not agree well in all cases. Discrepancies were due to the recording protocols of the systems. This may lead to incomparable results between instruments. It is therefore recommended that: (a) if different instruments are used in the same study or (b) multi-centre study designs are planned or (c) heart rate variability results are discussed with reference to studies using other instruments, levels of agreement need to be reported to ensure comparability.

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.

Influence of Intensive Cycling Training on Heart Rate Variability During Rest and Exercise

The current study examined whether changes in heart rate variability (HRV) following intensive cycling training contribute to the mechanism of training-induced bradycardia. Thirteen healthy untrained subjects, ages 18-27 years, underwent recordings of heart rate (HR) and [Formula: see text] before and after 8 weeks of cycling, 25-60 min/day, 5 days/week at > 80% maximum HR (HRmax). Heart rate recordings were obtained during supine rest and submaximal exercise and were analysed for the following components of HRV: low frequency (LF, 0.041-0.15 Hz); high frequency (HF, 0.15-0.40 Hz); LF/HF ratio and total power (TP, 0-0.40 Hz). At posttraining, VO2max was significantly increased while HR was significantly reduced at rest and all absolute exercise work rates. Training-induced lower HR was accompanied by significantly greater HF and TP during rest as well as LF, HF, and TP during all absolute exercise work rates. Posttraining HR and the majority of HRV measures were similar to pretraining values at the same relative exercise intensity (% HRmax). These results indicated that 8 weeks of intensive cycling training increased HRV and cardiac vagal modulation during rest and absolute exercise work rates but had little effect during relative exercise work rates. Increased vagal modulation resulting from intensive exercise training may contribute to the mechanism of training-induced bradycardia. Key words: exercise training, autonomic nervous system, bradycardia, vagal modulation