Heart rate variability in athletes

Autonomic control of heart rate during and after exercise : measurements and implications for monitoring training status

Endurance training decreases resting and submaximal heart rate, while maximum heart rate may decrease slightly or remain unchanged after training. The effect of endurance training on various indices of heart rate variability remains inconclusive. This may be due to the use of inconsistent analysis methodologies and different training programmes that make it difficult to compare the results of various studies and thus reach a consensus on the specific training effects on heart rate variability. Heart rate recovery after exercise involves a coordinated interaction of parasympathetic re-activation and sympathetic withdrawal. It has been shown that a delayed heart rate recovery is a strong predictor of mortality. Conversely, endurance-trained athletes have an accelerated heart rate recovery after exercise. Since the autonomic nervous system is interlinked with many other physiological systems, the responsiveness of the autonomic nervous system in maintaining homeostasis may provide useful information about the functional adaptations of the body. This review investigates the potential of using heart rate recovery as a measure of training-induced disturbances in autonomic control, which may provide useful information for training prescription.

Comparison of the Polar S810i monitor and the ECG for the analysis of heart rate variability in the time and frequency domains

The aim of the present study was to compare heart rate variability (HRV) at rest and during exercise using a temporal series obtained with the Polar S810i monitor and a signal from a LYNX(R) signal conditioner (BIO EMG 1000 model) with a channel configured for the acquisition of ECG signals. Fifteen healthy subjects aged 20.9 +/- 1.4 years were analyzed. The subjects remained at rest for 20 min and performed exercise for another 20 min with the workload selected to achieve 60% of submaximal heart rate. RR series were obtained for each individual with a Polar S810i instrument and with an ECG analyzed with a biological signal conditioner. The HRV indices (rMSSD, pNN50, LFnu, HFnu, and LF/HF) were calculated after signal processing and analysis. The unpaired Student t-test and intraclass correlation coefficient were used for data analysis. No statistically significant differences were observed when comparing the values analyzed by means of the two devices for HRV at rest and during exercise. The intraclass correlation coefficient demonstrated satisfactory correlation between the values obtained by the devices at rest (pNN50 = 0.994; rMSSD = 0.995; LFnu = 0.978; HFnu = 0.978; LF/HF = 0.982) and during exercise (pNN50 = 0.869; rMSSD = 0.929; LFnu = 0.973; HFnu = 0.973; LF/HF = 0.942). The calculation of HRV values by means of temporal series obtained from the Polar S810i instrument appears to be as reliable as those obtained by processing the ECG signal captured with a signal conditioner.

Alteration in left ventricular normal and shear strains evaluated by 2D-strain echocardiography in the athlete's heart

The contraction of cardiomyocytes induces a systolic increase in left ventricular (LV) normal (radial, circumferential and longitudinal) and shear strains, whose functional consequences have not been evaluated, so far, in athletes. We used 2D ultrasound speckle tracking imaging (STI) to evaluate LV regional strain in high-level cyclists compared to sedentary controls. Sixteen male elite cyclists and 23 sedentary controls underwent conventional, tissue Doppler, and STI echocardiography at rest. We assessed LV long and short axis normal strains and shear strains. We evaluated circumferential-longitudinal shear strain from LV torsion, and circumferential-radial shear strain from the difference between subendocardial and subepicardial torsion. Apical radial strain (42.7 +/- 10.5% versus 52.2 +/- 14.3%, P < 0.05) and LV torsion (6.0 +/- 1.8 deg versus 9.2 +/- 3.2 deg, P < 0.01) were lower in cyclists than in controls, respectively. Rotations and torsion were higher in the subendocardial than in the subepicardial region in sedentary controls, but not in cyclists. Haemodynamic and tissue Doppler based indexes of global LV diastolic and systolic functions were not different between cyclists and controls. Athlete's heart is associated with specific LV adaptation including lower apical strain and lower myocardial shear strains, with no change in global LV diastolic and systolic function. These mechanical alterations could improve the cardiovascular adjustments to exercise by increasing the radial strain and torsional (and thus untwisting) response to exercise, a key element of diastolic filling and thus of cardiac performance in athletes.

Supramaximal training and postexercise parasympathetic reactivation in adolescents

Repeated supramaximal exercise training is an efficient means of improving both aerobic and anaerobic energy system capacities. However, the influence of different levels of supramaximal training on parasympathetic function is unknown.

PURPOSE

To compare the effects of repeated-sprint (RS) versus high-intensity intermittent training (HIT) on performance and postexercise parasympathetic reactivation in trained adolescents.

METHODS

Fifteen male adolescents (15.6 +/- 0.8 yr) were divided into two groups that performed 9 wk of either RS (repeated all-out 6-s shuttle sprints; 14-20 s of recovery; N = 8) or HIT (15- to 20-s runs at 95% of the speed reached at the end of the 30-15 intermittent fitness test (V(IFT)); 15-20 s of recovery; N = 7). Groups performed intervals twice per week and maintained similar external training programs. Before and after training, performance was assessed by the V(IFT), countermovement jump (CMJ), 10-m sprint time (10 m), mean RS ability time (RSAmean), and heart rate (HRsub) level during a 6-min submaximal (60% V(IFT)) exercise test, where parasympathetic reactivation was assessed during the recovery phase (i.e., HR recovery time constant (HRRtau) and HR variability (HRV)).

RESULTS

Parasympathetic function, V(IFT), and RSAmean were improved with HIT but not RS training. In contrast, changes in CMJ and HRsub were similar in both groups. A significant relationship was shown between the decrease in HRRtau and RSAmean (r = 0.62, P < 0.05; N = 15).

CONCLUSION

HIT was more effective than RS training at improving postexercise parasympathetic function and physical performance. In addition, HRRtau, which was more sensitive to training than HRV indices, seems to be a useful performance-related measurement.

Complexity of heartbeat interval series in young healthy trained and untrained men

The origin of heart rate variability (HRV) is largely in parasympathetic activity. The direct influence of sympathetic activity and other control mechanisms, especially at an increased HR, is not well understood. The objectives of the study were to investigate the influence of increasing HR on the properties of heartbeat interval (RR) series in young healthy subjects. ECG was recorded in 9 trained and 11 untrained young men during supine rest, standing, incremental running exercise and relaxation. During exercise, a breath-to-breath gas exchange was monitored. The RR time series analysis included the spectral analysis, detrended fluctuations analysis method and sample entropy (SampEn) calculation. During exercise, spectral powers were reduced dramatically in both groups. The dependence of short-term scaling exponent (alpha(1)) on the RR included a characteristic maximum, while SampEn for the same value of the RR had a minimum. The value of HR corresponding to the maximum of alpha(1) and minimum of SampEn (IHR) corresponded to the intrinsic HR obtained by an autonomic blockade. In trained subjects, the curves alpha(1) versus RR and SampEn versus RR were moved toward larger RR, compared with control. For HR values higher than IHR, alpha(1) decreased and SampEn increased. These results reveal that the complexity of the heart rhythm above intrinsic HR decreases with an increase in HR. We suggest that at the highest HR intrinsic heart control is reflected in the heart rhythm. We point out the possibility of developing a new non-invasive method for the determination of intrinsic HR from the curve alpha(1) versus RR.

Heart rate variability as a measure of disease state in irritable bowel syndrome

Heart rate variability (HRV) is a noninvasive measure of sympathovagal balance in the autonomic nervous system (ANS). This review will: (a) consider HRV measurement in irritable bowel syndrome (IBS); (b) discuss the applicability of HRV measurement in IBS by addressing strengths and limitations; and (c) propose future directions in this field of gastrointestinal research and clinical practice. As a strength, analyzing HRV components is a useful method and appears most suitable for detection of changes in ANS sympathovagal balance in both stress and non-stress conditions with good validity and reliability. Also, it is an appropriate measure for ANS in studies with large populations, in both laboratory and clinical settings, and for longitudinal studies because of its noninvasive assets. With regard to limitations of measuring HRV, these are poor standardization, additional human editing, not considering medication or other confounding factors, inconsistent results in gastrointestinal vagal tone study, and different time periods.

Peculiarities of the autonomic balance assessed through heart rate variability analysis in sportsmen and nonsportsmen

A comparative study was used to analyze the difference in autonomic balance assessed by time and frequency domain parameters of heart rate variability (HRV) between students athletes and non-sportsmen. Five-minute digital ECG trays were recorded in 21 students - athletes, 10 basketball players recruited from first league clubs of No- vi Sad and the Serbian representatives and 11 rowers from the Novi Sad rowing club 'Danubius'. The control group was formed by 15 non-sportsmen, students of the Medical faculty in Novi Sad who underwent the same registrations. Time and frequency-domain of HRV were analyzed by a software developed by the company 'Neurosoft', VNS-Spektr, Ivanovo, Russia. Resting heart rate in athletes was significantly lower (p < 0.01) than in non-sportsmen. In time-domain parameters HRV significantly higher values were present in the group of sportsmen as opposed to non-sportsmen RRNN (p < 0.01), RMSSD (p < 0.02) and pNN50 (p < 0.01). In frequency-domain of HRV statistically significant difference between the two groups was observed only in normalized values of LF and HF (p < 0.05) and their ratio LF/HF (p < 0.02). LFn was larger in non-sportsmen than in students-athletes. On the other hand HFn was larger in athletes than in non-sportsmen. The LF/HF ratio was larger in non-sportsmen (2.87 0.34) than in athletes (1.91 0.20). After dividing the athletes recruited for this investigation into two groups (basketball players and rowers) significant level of difference (p < 0.05) in HRV data was present only in the VLF spectrum (2060.55 290.68 ms2 for rowers and 1303.30 ? 169.95 ms2 for basketball players).

No Effect of Training State on Ambulatory Measures of Cardiac Autonomic Control

We examined the effect of training state on cardiac autonomic control in a naturalistic setting. Twenty-four vigorous exercisers were compared to age- and sex-matched sedentary controls. The regular exercisers were subjected to a 6-week training program after which they were randomized to 2 weeks of continued training or 2 weeks of detraining. Cardiac autonomic control was measured over a 24-h period by ambulatory recording, using the preejection period (PEP) and respiratory sinus arrhythmia (RSA). Nonexercising controls had a significantly higher ambulatory heart rate (HR) compared to the regular exercisers but comparable 24-h levels of PEP and RSA. In regular exercisers, 2 weeks of detraining did not significantly change the 24-h levels of HR, PEP, or RSA. We conclude that the bradycardia in healthy regular exercisers is the result of a lower intrinsic heart rate rather than a shift in cardiac autonomic balance from sympathetic to vagal control.

Autonomic recovery after exercise in trained athletes: intensity and duration effects

PURPOSE

To investigate the effects of training intensity and duration, through a range representative of training in endurance athletes, on acute recovery of autonomic nervous system (ANS) balance after exercise.

METHODS

Nine highly trained (HT) male runners (VO2max 72 +/- 5 mL.kg.min(-1), 14 +/- 3 training hours per week) and eight trained (T) male subjects (VO2max 60 +/- 5 mL.kg.min(-1), 7 +/- 1 training hours per week) completed preliminary testing to determine ventilatory thresholds (VT1, VT2) and VO2max. HT performed four intensity-controlled training sessions: 60 min and 120 min below VT1; 60 min with 30 min between VT1 and VT2 (threshold); and 60 min above VT2 (6 x 3 min at 96% VO2max, 2 min of recovery). T also completed the interval session to compare ANS recovery between HT and T. Supine heart rate variability (HRV) was quantified at regular intervals through 4 h of recovery.

RESULTS

When HT ran 60 or 120 min below VT1, HRV returned to pretraining values within 5-10 min. However, training at threshold (2.7 +/- 0.4 mM) or above VT2 (7.1 +/- 0.7 mM) induced a significant, but essentially identical, delay of HRV recovery (return to baseline by approximately 30 min). In T, HRV recovery was significantly slower, with HRV returning to baseline by >or=90 min after the same interval session.

CONCLUSIONS

In the highly trained endurance athlete, exercise for <or=120 min below the first ventilatory threshold causes minimal disturbance in ANS balance. ANS recovery is more rapid in highly trained than in trained subjects after high-intensity exercise. Further, the first ventilatory threshold may demarcate a "binary" threshold for ANS/HRV recovery in highly trained athletes, because further delays in HRV recovery with even higher training intensities were not observed.

Dinâmica não-linear e exercício físico: conceitos e aplicações

Médicos, fisiologistas, bioquímicos, psicólogos e até profissionais envolvidos com exercício físico estão recentemente aumentando seus interesses pela dinâmica não-linear, uma teoria científica desenvolvida principalmente por matemáticos, que é genericamente conhecida por Teoria da Complexidade. Embora poucos trabalhos em Educação Física e Esporte utilizem esse paradigma para solucionar seus problemas, nota-se um crescente interesse por esse mesmo enfoque, principalmente em relação aos efeitos do exercício físico sobre mudanças na variabilidade e complexidade de séries temporais fisiológicas. Geralmente, tais mudanças se revelam na forma de queda em seu comportamento temporal, denotando diminuição na complexidade do organismo ou de componentes envolvidos especificamente na sua regulação. De acordo com a Teoria da Complexidade, por enfatizar interações não-lineares existentes em sistemas biológicos, verifica-se que não é importante apenas a elevação (supercompensação) de componentes do organismo com a prática de exercícios físicos, mas também aqueles que atrofiam (descompensação) paralelamente, porque podem contribuir para a ocorrência de perda de sincronia na funcionalidade desses sistemas. Assim, em oposição à ênfase que se dá no treinamento físico à repetição monótona de atividade física intensa e voltada para efeitos específicos positivos, que invariavelmente leva à simplificação do organismo, recomenda-se maior variação qualitativa e quantitativa nos exercícios praticados. O objetivo é preservar sua complexidade natural ou impedir que ocorra diminuição rápida com o envelhecimento. A presente revisão tem por objetivo, além de descrever a possível perda de complexidade com o treinamento físico, discutir alguns conceitos da Teoria da Complexidade de modo introdutório, com particular ênfase em tópicos envolvendo saúde e desempenho físico.

Changes in heart rate recovery in response to acute changes in training load

Heart rate recovery is an indirect marker of autonomic function and changes therein may offer a practical way of quantifying the physiological effects of training. We assessed whether per cent heart rate recovery (HRr%) after a standardized sub-maximal running (Heart rate Interval Monitoring System: HIMS) test, changed with acute changes in training load. A total of 28 men and women (mean age 30+/-5 years) trained ad libitum for 2 weeks during which their heart rate (HR) was recorded. Training load was quantified using Training Impulse (TRIMPs). The participants were grouped based on whether they increased (Group I, n=9), decreased (Group D, n=8) or kept their training load constant (Group S, n=11) from week 1 to week 2. Each week, the subjects completed a HIMS test. Changes between weeks in HR at the end of the test and HRr% were compared between groups. Mean per cent change in TRIMPs from week 1 to week 2 was significantly different among the groups (Group I, 55+/-21% vs Group S, -6+/-6% vs Group D, -42+/-16%; P<0.05). Group I had a slower HRr% and Group D tended to have a slightly faster HRr% after HIMS 2 than after HIMS 1 (mean per cent change 5.6+/-8.7 vs -2.6+/-3.9; P=0.03). Thus a negative effect on HRr was observed with increases in training load. Sub-maximal HR was not affected by acute changes in training load. Whereas HR during exercise measures cardiac load, HRr may reflect the state of the autonomic nervous system, indicating the body's capacity to respond to exercise.

Caracterização da variabilidade de freqüência cardíaca e sensibilidade do barorreflexo em indivíduos sedentários e atletas do sexo masculino

INTRODUÇÃO: A capacidade de variar a freqüência cardíaca representa importante papel fisiológico na vida diária. As variações dos intervalos RR estão na dependência de moduladores biológicos, como o sistema nervoso autônomo. Essas variações constituem a variabilidade da freqüência cardíaca (VFC). MÉTODOS: 10 indivíduos atletas (Atl) e 10 sedentários (Sed) (20-35 anos) foram submetidos a eletrocardiografia digital, em repouso, antes, durante e após a manobra. Os valores de RR foram tratados (software Matlab 6.1), no domínio do tempo. RESULTADOS: Os grupos Sed e Atl apresentaram freqüência cardíaca média igual a 73,59bpm ± 2,5 e 51,01bpm ± 2,4, respectivamente. Quanto aos intervalos RR, o grupo de Sed apresentou média de 826,58ms ± 5,3 e o grupo Atl, 1.189,18 ± 6,9. O tempo de retorno simpático após a manobra 72 ± 12s (Sed) 37 ± 6s (Atl). O tempo de retorno parassimpático foi de 80 ± 11s (Sed) 40 ± 8s (Atl). O pNN50 foi de 10 ± 3,3 (Sed) e 42,10 ± 6,9 (Atl). O valor da variação dos RR acima da média de todo o sinal foi de 343 ± 40ms (Sed) e 175 ± 39ms (Atl). A variação abaixo da média de todo o sinal foi de 281 ± 27ms (Sed) e 425 ± 26ms (Atl). CONCLUSÕES: A análise da VFC associada à manobra de Valsalva pode representar uma ferramenta simples, mas importante, para possíveis inferências sobre aptidão física.

Heart rate variability in trotters during different training periods

REASONS FOR PERFORMING STUDY

Endurance training induces changes in autonomic nervous system functions. High intensity training includes the risk of overtraining, in man and horse. Heart rate variability (HRV) is a noninvasive measurement of the autonomic regulation of the heart rate, which is quick and easy to measure with modern telemetric technology.

HYPOTHESIS

Since HRV is affected by changes in the autonomic nervous system, it might be an early stage indicator of poor recovery from a previous bout of exercise or overreaching or overtraining in horses in general.

METHODS

The aim of the study was to monitor recovery and the possible overtraining status in horses by measuring HRV. The measurements reflected the responses of the previous day activities during different training periods including basic training, precompetition and competition during a one-year follow-up.

RESULTS

HRV was at the highest during precompetition period (P<0.05) and it decreased significantly during competition period (P<0.05), indicating an increased stress load in the competition period. Walking increased HRV significantly compared to complete rest or jogging as previous day activities during basic training and precompetition periods (P<0.05). This finding suggests that horses are more relaxed during moderate exercise than standing still or anaerobic exercise.

CONCLUSIONS

HRV can be used to monitor the cardiovascular responses to training in horses but confirmatory measures may also be required in addition to HRV to exclude other possible causes of underperformance.

Is aerobic endurance a determinant of cardiac autonomic regulation?

The aim of this study was to determine if subjects matched for VO2max but with differing aerobic endurance displayed similar heart rate variability (HRV) at rest and heart rate recovery (HRR) after maximal exercise. We hypothesized that the higher the aerobic endurance, the higher the HRV and the faster the HRR. Twenty-eight well trained middle- and long-distance runners (24 men and 4 women) performed a maximal continuous graded exercise test for the determination of maximal oxygen consumption (VO2max), ventilatory threshold (VT), peak treadmill velocity (PTV) and HRR, as well as a test to measure the autonomic regulation of heart rate during supine rest, using HRV analysis. Once both tests were completed, subjects were matched for VO2max and assigned to the low endurance or the high endurance group, depending on the %PTV at which VT occurred (81.9 +/- 2.9 and 88.3 +/- 3.1%PTV for both groups, respectively; P < 0.0001). Contrary to our hypotheses, neither HRV nor HRR parameters were different between groups or associated with aerobic endurance. VO2max (59.0+/-7.3 ml min(-1) kg(-1)) was inversely correlated with ln SDNN (r = -0.44, P < 0.05), ln HF (r = -0.52, P < 0.05), ln LF + HF (r = -0.53, P < 0.05). These results suggest that aerobic endurance is not associated with cardiovascular autonomic control, as measured by HRV and HRR.

Effects of exercise training on heart rate and QT interval in healthy young individuals: are there gender differences?

AIMS

The aim of the present study was to assess the effects of exercise training on heart rate, QT interval, and on the relation between ventricular repolarization and heart rate in men and women.

METHODS AND RESULTS

A 24 h Holter recording was obtained in 80 healthy subjects (40 males) who differed for the degree of physical activity. Trained individuals showed a lower heart rate and a higher heart rate variability than sedentary subjects, independent of the gender difference in basal heart rate. Mean 24 h QTc was similar in trained and non-trained men, while a significant difference was observed between trained and non-trained women. Exercise training reduced the QT/RR slope in both genders. This effect on the QT/RR relation was more marked in women; in fact, the gender difference in the ventricular repolarization duration at low heart rate observed in sedentary subjects was no longer present among trained individuals.

CONCLUSION

The results of this study suggest that the cardiovascular response to exercise training may be different in men and women. Women may benefit more from interventions aimed to increase physical activity as a tool for prevention of cardiovascular morbidity and mortality.

Rate of reduction of heart rate variability during exercise as an index of physical work capacity

Breathing rates during physical exercise suggest that, during these conditions, the high-frequency (HF) bandwidth of heart rate variability (HRV) analysis should be extended beyond conventional guidelines. However, there has been little investigation of the most appropriate choice of HF bandwidth during exercise. HRV analysis was performed in 10 males and six females during progressive bicycle exercise. Cardiac cycle (RR) interval and breath-by-breath respiratory data were simultaneously recorded. HRV powers were determined for the band-limited ranges 0.04-0.15 Hz [low-frequency (LF)], 0.15-0.4 Hz (HF 0.4) and 0.15-bf Hz (HF bf, where bf represents maximum breathing frequency). Mono-exponential functions described the relationship between HRV and work rate for each bandwidth (r=0.92-0.95) and were used to calculate the "HRV decay constant" (work rate associated with a 50% reduction in HRV power). The HRV decay constants for each bandwidth were linearly related to maximal work rate (r>0.71; P<0.001) and were substantially greater in males than in females (P<0.001). There was a significant difference between the HRV decay constants for HF 0.4 and HF bf (P<0.005) in both genders. The HRV decay constants for the LF and HF bf bandwidths appear to provide an indication of work capacity from submaximal exercise, without prior assumption regarding heart rate and its relationship with work rate.

Estimation of the Uncertainty in Time Domain Indices of RR Time Series

A method for estimating the uncertainty in time-domain indices of RR time series is described. The method relies on the central limit theorem that states that the distribution of a sample average of independent samples has an uncertainty that asymptotically approaches to the sample standard deviation divided by the square root of the number of samples. Because RR time series cannot be characterized by a set of independent samples, we propose to estimate the uncertainty of indices by computing them in blocks that satisfy that the obtained partial indices are independent. We propose a methodology to search sets of independent partial indices and apply this methodology to the estimation of the uncertainty in the mean RR, SDRR, and r-msDD indices. The results show that the uncertainty can be higher than the 10% of the index for the SDRR and even higher for the r-msDD. Moreover, a statistical test for the difference of two indices is proposed.

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.

Resting and Postexercise Cardiac Autonomic Control in Trained Masters Athletes

This study used measures of heart rate variability during recovery from high-intensity exercise in trained Master athletes to examine postexercise cardiac autonomic regulation. Seven males (mean age 52.1 +/- 3.3 yr; mass 85.1 +/- 18.0 kg) and 6 females (mean age 50.5 +/- 2.9 yr; mass 63.1 +/- 6.0 kg) performed incremental exercise to an intensity that induced a >4.5 mmol capillary blood lactate concentration, followed by incremental exercise to volitional exhaustion (VO2(max)). A 6 min ECG recording before (Pre) and after (Post) exercise was analyzed in the time (mean rr interval, sd rr) and frequency domains (total power, very low frequency [VLF: 0-0.04 Hz], low frequency [LF: 0.04-0.15 Hz], high frequency [HF: 0.15-0.4 Hz]). VO2(max) for males and females was 49.4 +/- 7.1 ml kg(-1) min(-1) and 45.1 +/- 10.1 ml kg(-1) min(-1), respectively. Lower mean rr interval (Pre: 1,048 +/- 128 ms; Post: 730 +/- 78 ms; P < 0.001) and lower sd rr (Pre: 77 +/- 30 ms; Post: 43 +/- 17 ms; P < 0.001) were recorded following exercise, with no differences based on gender. Total power decreased following exercise (Pre: 6,331 +/- 6,119 ms; Post: 1,921 +/- 1,552 ms). When normalized for changes in total power, a decreased HF component (Pre: 34.52 +/- 14.79 n.u.; Post: 18.49 +/- 13.64 n.u.; P < 0.05) with no change in LF component (Pre: 61.00 +/- 18.66 n.u.; Post: 69.63 +/- 23.97 n.u.; P = 0.34) was recorded. No gender differences in HRV in the frequency domain were recorded. Decreased heart rate variability in both time and frequency domains suggested an increased parasympathetic withdrawal during the autonomic control of postexercise tachycardia in trained Master athletes.

Heart rate turbulence and heart rate variability in patients with mitral valve prolapse

AIMS

Heart rate turbulence (HRT) and heart rate variability (HRV) have been shown to be independent and powerful predictors of mortality in a specific group of cardiac patients. However, the predictive values of HRV alone is modest and information on HRV in patients with mitral valve prolapse (MVP) has so far been conflicting. In addition, no studies have previously evaluated HRT in patients with MVP. To define better the effects of MVP on cardiac autonomic function, we assessed HRT and time-domain parameters of HRV in patients with MVP.

METHODS AND RESULTS

Fifty patients with MVP and 70 controls without MVP were investigated. The diagnosis of MVP was confirmed by cross-sectional echocardiography in the parasternal long-axis view and apical 4-chamber view. The HRV and turbulence analysis were assessed from a 24-hour Holter recording. When HRT parameters were compared, the values of the HRT onset and slope were significantly lower in MVP patients than in the controls group (-0.109+/-0.207 vs. -0.289+/-0.170%, P=0.001 and 8.6+/-7.2 vs. 11.5+/-7.4 ms/RRI, P=0.043, respectively) and the number of patients who had abnormal HRT onset was significantly higher in the MVP group than in controls (15 vs. 8, P=0.011). In addition, HRV parameters were not statistically different between the two groups.

CONCLUSION

Although we found that the decrease in HRV parameters was not significantly different between MVP patients and controls, HRT variables (especially HRT onset) were significantly lower in MVP patients. Therefore, in our opinion, HRT is an attractive, easily applicable, and better way of non-invasive risk prediction compared with another non-invasive risk predictor, HRV.

Cardiac parasympathetic regulation: respective associations with cardiorespiratory fitness and training load

The objective of this study was to establish the separate associations between parasympathetic modulations of the heart [evaluated through heart rate (HR) variability (HRV) indexes and postexercise HR recovery (HRR) indexes] with cardiorespiratory fitness and training load. We have measured cardiorespiratory fitness through peak oxygen consumption (V̇o2 max) and estimated weekly training load with the Baecke sport score in 55 middle-aged individuals (30.8 ± 1.8 yr, body mass index 24.5 ± 0.4 kg/m2). HRV indexes were analyzed at rest under controlled breathing, and HRR was estimated from HR curve fitting after maximal exercise or from measurements of the number of beats recovered at 60 s after exercise. Multiple linear regressions were used to investigate the separate relationships between vagal-related HRV indexes and V̇o2 max and Baecke scores. On the basis of their V̇o2 max and Baecke scores, subjects were classified as fit or unfit and as low trained (LT) or moderately trained (MT), which yielded four groups: UnfitLT, UnfitMT, FitLT, and FitMT. Vagal-related HRV indexes were positively correlated with V̇o2 max ( P < 0.05) but not with Baecke scores. In contrast, HRR indexes were related to Baecke scores ( P < 0.05) but not with V̇o2 max. FitLT and FitMT had significantly higher ( P < 0.05) normalized vagal-related HRV indexes than UnfitLT and UnfitMT, but HRR did not change. Moderate training was associated with significantly lower HRR indexes both in UnfitMT and FitMT compared with UnfitLT and FitLT, but there was no difference in vagal-related HRV indexes. These results indicate that vagal-related HRV indexes are related more to cardiorespiratory fitness, whereas HRR appears to be better associated with training load.

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

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

Maternal fish oil supplementation during lactation does not affect blood pressure, pulse wave velocity, or heart rate variability in 2.5-y-old children

Maternal (n-3) PUFA deficiency is associated with higher blood pressure (BP) later in life in rat offspring, and early intake of (n-3) PUFA in formula-fed infants was shown to modify later BP. BP, heart rate (HR), and heart rate variability (HRV) are affected by dietary (n-3) PUFA in adults. In this study, we investigated whether fish oil (FO) supplementation of lactating mothers could modify BP, pulse wave velocity (PWV), and HRV in their children after 2 y. Mothers with low fish intake were randomly assigned to FO or olive oil (OO) supplementation for the first 4 mo after delivery. A reference group of mothers with a high habitual fish intake (HFI) was also followed. At the follow-up study at 2.5 y of age, BP and PWV were measured, and electrocardiograms were recorded for 0.5 h. FO supplementation significantly increased RBC levels of long-chain (n-3) PUFA of the 4 mo-old children, but at 2.5 y, the FO and OO groups did not differ. BP, PWV, HR, and HRV also did not differ among the groups. However, for all 3 groups, the children's intake of (n-3) PUFA at 2.5 y was negatively correlated with mean arterial pressure after adjustment for outdoor temperature (r = -0.245, P = 0.04). In conclusion, maternal FO supplementation had no overall effect on BP, PWV, or HRV of the children, indicating that (n-3) PUFA intake of Danish mothers may be sufficient in this sense. However, children's dietary intake of (n-3) PUFA might have a beneficial effect on BP in childhood.

Seasonal training and heart rate and blood pressure variabilities in young swimmers

To evaluate if changes in athletes' physical fitness due to seasonal training are associated with changes in cardiovascular autonomic control, nine swimmers (three males and six females; aged 14-18 years) were evaluated before and after 5 months of training and competitions. Maximal oxygen consumption (VO2max) and ventilatory threshold were determined during a maximal test; heart rate (HR) and blood pressure (BP) variabilities' power spectra were calculated at rest (supine and sitting positions) and in the recovery of two exercises at 25 and 80% pre-training VO2max. At the end of the season: (a) VO2max and ventilatory threshold increased respectively by 12 and 34% (P<0.05); (b) at rest, HR decreased by 9 b min(-1) in both body positions, whereas BP decreased in supine position only by 17%. No change in low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-1.5 Hz) normalized powers and in LF/HF ratio of HR variability and in LF power of systolic BP variability was observed. In contrast, a significant increase in HF alpha-index (about 12 ms mmHg(-1)) was found; (c) during recovery no change in any parameter was observed. Seasonal training improved exercise capacity and decreased resting cardiovascular parameters, but did not modify vagal and sympathetic spectral markers. The increase in alpha-index observed at rest after the season and expression of augmented baroreflex sensibility indicated however that HR vagal control could have been enhanced by seasonal training. These findings suggested that autonomic system might have played a role in short-term adaptation to training.

Is slow wave sleep an appropriate recording condition for heart rate variability analysis?

Heart rate variability (HRV) analysis holds increasing interest but electrocardiographic (ECG) recordings are strongly disturbed by body movements, changes in environment and respiration. Here we give arguments for the use of slow wave sleep (SWS) as an appropriate recording condition. Sixteen healthy subjects aged 21-31 years (10 males, 6 females) underwent polygraphic sleep, ECG, and respiratory recordings during one experimental night. HRV was analyzed in 5-min SWS segments and compared to data collected during quiet wake in the morning with controlled breathing, using for each individual the same respiratory frequency as that recorded during SWS. SWS has two major advantages. First, it is a quiet sleep period, free of any external confounding events and is characterized by fewer body movements or arousals that cause abrupt heart rate (HR) increases which disrupt the ECG signal. Second, SWS avoids the deleterious effect of controlled breathing on HRV. Respiratory cycles were spontaneously more regular during SWS than during generally used wake (Standard deviation (SD) of the respiratory cycles was 0.27+/-0.02 s during SWS vs 0.42+/-0.07 s during wake under controlled breathing; p<0.01). Compared to quiet wake, the SD of normal R-R intervals reflecting global variability was significantly lower during SWS (54.3+/-4.7 vs 78.8+/-6.1 ms; p<0.001) and the normalized high frequency power was increased (0.57+/-0.04 vs 0.51+/-0.03; p<0.05), suggesting a higher parasympathetic control of the heart. Thus, SWS offers a "self-controlled" and undisturbed moment of observation for assessing time and frequency domain HRV indexes. Its relevance as an optimal ECG recording condition has to be confirmed in various experimental conditions.

Effect of intensive training on heart rate variability in prepubertal swimmers

BACKGROUND

In children, there is very limited evidence focusing on the beneficial effect of exercise training on heart rate variability (HRV) during childhood. Despite the fact that more and more children are engaged in intensive training programs, the question arises if such intensive training involves deleterious effects on the cardiac autonomic nervous system during childhood. Thus the aim of the present study was to compare HRV parameters in highly trained swimmer boys and untrained counterparts.

METHODS

Twenty prepubertal boys, aged 11-12 years old, took part in the study. The children were divided into 11 highly trained prepubertal swimmers (training sessions of 8-10 h weekly for at least 4 years) and 9 age-matched active boys. HRV analysis was performed on diurnal recordings in the frequency (short-term recordings 6 min the most 'vagal') and time (long-term recordings 4 h centred on the 6 min most 'vagal') domains.

RESULTS

No significant differences were obtained between groups for all frequency variables whatever the mode of expression (absolute in ms2, relative in Ln or %). All time-domain components were not significantly different in swimmers and untrained boys.

CONCLUSIONS

The results of the present study demonstrate that participating intensively in swimming training does not induce in children changes in HRV indices. Neither time nor domain HRV variables were significantly different between untrained and highly trained prepubertal boys. Thus, intensive training in healthy children does not involve deleterious effects on HRV.

Analysis of week-to-week variability in skin blood flow measurements using wavelet transforms

The study of skin blood flow responses is confounded by temporal variability in blood flow measurements. Spectral analysis has been shown useful in isolating the effects of distinct control mechanisms on various stimuli in the microcirculatory system. However, the sensitivity of spectral analysis to temporal blood blow variability has not been reported. This study was designed to assess week-to-week variability in blood flow measurements using wavelet-based spectrum analysis. Ten healthy, young subjects (mean age+/-SD, 30.0+/-3.1 years) were recruited into the study. Incremental heating (35-45 degrees C, 1 degrees step min-1) was applied on the skin over the sacrum once per week for three consecutive weeks. Wavelet analysis was used to decompose the laser Doppler blood flow signal into frequency bands determined to be associated with endothelial nitric oxide (0.008-0.02 Hz), neurogenic (0.02-0.05 Hz), myogenic (0.05-0.15 Hz), respiratory (0.15-0.4 Hz), and cardiac (0.4-2.0 Hz) control mechanisms. The results showed that coefficients of variation for the power in each frequency band at baseline are smaller than the coefficients of variation of blood flow at baseline or at maximal blood flow ratio (P<0.05). Myogenic and respiratory frequency bands showed the highest coefficients of variation among the five frequency bands. An increase in power in the endothelial nitric oxide frequency band and a decrease in power in the myogenic frequency band of the maximal blood flow response were reproduced in three consecutive weeks. Our study suggests that wavelet analysis is an effective method to overcome temporal variability in skin blood flow measurements.

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.

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.

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.

Effects of increased training load on vagal-related indexes of heart rate variability: a novel sleep approach

There is little doubt that moderate training improves cardiac vagal activity and thus has a cardioprotective effect against lethal arrhythmias. Our purpose was to learn whether a higher training load would further increase this beneficial effect. Cardiac autonomic control was inferred from heart rate variability (HRV) and analyzed in three groups of young subjects (24.5 ± 3.0 yr) with different training states in a period free of stressful stimuli or overload. HRV was analyzed in 5-min segments during slow-wave sleep (SWS, a parasympathetic state that offers high electrocardiographic stationarity) and compared with data collected during quiet waking periods in the morning. Sleep parameters, fatigue, and stress levels checked by questionnaire were identical for all three groups with no signs of overtraining in the highly trained (HT) participants. During SWS, a significant ( P < 0.05) increase in absolute and normalized vagal-related HRV indexes was observed in moderately trained (MT) individuals compared with sedentary (Sed) subjects; this increase did not persist in HT athletes. During waking periods, most of the absolute HRV indexes indistinctly increased in MT individuals compared with controls ( P < 0.05) but did not increase in HT athletes. Normalized spectral HRV indexes did not change significantly among the three groups. Heart rate was similar for MT and Sed subjects but was significantly ( P < 0.05) lower in HT athletes under both recording conditions. These results indicate that SWS discriminates the state of sympathovagal balance better than waking periods. A moderate training load is sufficient to increase vagal-related HRV indexes. However, in HT individuals, despite lower heart rate, vagal-related HRV indexes return to Sed values even in the absence of competition, fatigue, or overload.