Influence of short-term endurance exercise training on heart rate variability

PURPOSE: To examine the influence of 2 wk (eight sessions) of endurance training on cardiac autonomic modulation, as measured by heart rate variability (HRV). METHODS: Twenty-four males (mean age: 23.1 yr) were randomized to an exercise (EX; N = 12) or control group (CT; N = 12). EX trained for eight sessions (4x wk-1, 40 min, 80-85% HRreserve) on a cycle ergometer. ECG tracings were collected during 5 min of paced breathing (12 breaths x min-1 (PB)), 5 min of spontaneous breathing (SB1), 5 min of 70 degrees head-up tilt (TILT), and a second 5-min period of spontaneous breathing (SB2). Data were collected before (test 1), during (tests 2-4), and 48 h after (test 5) the 2-wk period. HRV was reported as the standard deviation of RR intervals, and as natural logarithm of the normalized units (NU) of high- and low-frequency power (lnHF and lnLF). RESULTS: EX exhibited a significant increase in peak oxygen consumption (8%). During PB and TILT conditions, ANOVA revealed a group x time interaction such that EX exhibited lower lnLFNU and lnLF/lnHF during test 5 compared with test 1. CONCLUSION: These data suggest that eight endurance exercise-training sessions performed over 2 wk enhance the relative vagal modulation of the heart during PB and TILT, but not during SB.     

Effect of acute hypoxia on heart rate variability at rest and during exercise

The purpose of this study was to investigate sympathovagal balance as inferred from heart rate variability (HRV) responses to acute hypoxia at rest and during exercise. HRV was evaluated in 12 healthy subjects during a standardized hypoxic tolerance test which consists of four periods alternating rest and moderate exercise (50 % V.O (2)max) in normoxic and hypoxic conditions. Ventilatory responses were determined and HRV indexes were calculated for the last 5 min of each period. In well-tolerant subjects, hypoxia at rest induced a decrease of root-mean-square of successive normal R-R interval differences (RMSSD) (p < 0.05) and of absolute high frequency (HF) power (p < 0.001). All absolute HRV indexes were strongly reduced during exercise (p < 0.001) with no further changes under the additional stimulus of hypoxia. A significant increase (p < 0.05) in the HF/(LF+HF) ratio (where LF is low frequency power) was found during exercise in hypoxia compared to exercise in normoxia, associated with similar mean changes in ventilation and tidal volume. These results indicate a vagal control withdrawal under hypoxia at rest. During exercise at 50 % V.O (2)max, HRV indexes cannot adequately represent cardiac autonomic adaptation to acute hypoxia, or possibly to other additional stimuli, due to the dominant effect of exercise and the eventual influence of confounding factors.     

Spectral analysis of heart rate variability during exercise in trained subjects

PURPOSE: To investigate the effects of strenuous exercise on heart rate variability (HRV). METHODS: We evaluated the effects of exercise intensity and duration on HRV indices in 14 healthy trained subjects. Each subject exercised for 3, 6, and 9 min at 60 and 70% of the power achieved at maximal oxygen consumption (PVO2(max)) and for 3 and 6 min (or 3 min twice) at 80% of PVO2(max). The electrocardiogram RR intervals were recorded then processed by fast(FFT) and short-time (STFT) Fourier transform for determination of low-frequency (LF, 0.045-0.15 Hz) and high-frequency (HF, 0.15-1.0 Hz) components. RESULTS: The LF and HF components expressed as absolute power (ms2) decreased significantly at the onset of exercise (P < 0.05). However, with increasing exercise intensity, the HF component expressed as normalized units (n.u.) (reflecting parasympathetic modulation) increased significantly, whereas the LF component (n.u.) and LF/HF ratio (both reflecting sympathetic modulation) decreased significantly (P < 0.05). STFT showed that increasing exercise intensity was associated with a shift in HF peak frequency related to an increase in respiratory rate and a marked decrease in LF power (ms2). Moreover, HFn.u. rose (r = 0.918, P < 0.01) and LFms2 fell as minute ventilation increased (r = 0.906, P < 0.01). CONCLUSIONS: Parasympathetic respiratory control and nonautonomic mechanisms may influence the HF-peak shift during strenuous exercise. HRV and the usual indexes of sympathetic activity do not accurately reflect changes in autonomic modulation during exhaustive exercise.     

Effect of training and detraining on heart rate variability in healthy young men

The purpose of this study was to investigate the effect of twelve weeks of aerobic training and eight weeks of training cessation on Heart Rate Variability (HRV). Ten healthy young men (Age: 21.7 +/- 2.2 years; Height: 179.2 +/- 6.9 cm; Mass 72.7 +/- 11.1 kg) completed an incremental test and a 60 degrees tilt test during which R-R intervals were recorded before (T0) and after (T12) 12 weeks of intensive training, and after 2, 4 and 8 weeks of training cessation (D2, D4 and D8, respectively). HRV was computed in time and frequency domains. Training resulted in a significant increase in estimated VO2max after T12 (p < 0.01), followed by a significant decrease during D2 and D8 (p < 0.05). Total power (LF + HF) and low frequency power (LF) increased significantly in the supine position after the training period (p < 0.05) and decreased moderately after D2 (p > 0.05) to stabilize afterwards. LF + HF and LF were not different from T0 at D8 (p > 0.05). It was concluded that eight weeks of training cessation allow to reverse the cardiovascular autonomic adaptations induced by 12 weeks of intensive training in healthy young men.     

Heart rate variability, training variation and performance in elite swimmers

The aim of the present study was to investigate the relationships between heart rate variability (HRV) changes and both training variations and performances in elite swimmers. A secondary purpose was to measure catecholamine urinary excretion in elite swimmers to validate the HRV indices of sympathetic activity during training. Thirteen swimmers (4 females and 9 males) were tested before and after 4 weeks of intense training (IT) and 3 weeks of reduced training (RT). At the end of each period, the swimmers participated in an official competition of their best event. Individual performances were expressed as percentage of the previous season's best performance. Spectral analysis was used to investigate RR interval variability. HRV indices failed to show any significant changes between the study periods (p>0.05). Pre-IT HF was correlated with performance (r=0.45; p=0.05) and HFnu (r=0.59; p<0.05) during RT. On the other hand, once RT was completed, HFnu was correlated positively to performance (r=0.81; p<0.01) and negatively to fatigue (r=- 0.63; p<0.03). Conversely, the indices of sympathetic activity, i.e., LFnu and LF/HF ratio were inversely related to performance (both r=- 0.81; p<0.01); total fatigue score was correlated to the changes in HFnu (r=- 0.63; p<0.03) and in the LF/HF ratio (r=0.58; p<0.05). Changes in the adrenaline/noradrenaline ratio over the follow-up period were related to the changes in the LF/HF ratio (r=0.45; p<0.03). In highly trained swimmers coping well with a training program, including 4 weeks of IT followed by 3 weeks of RT, HRV indices were unaltered. On the other hand, after the 3 weeks of RT, HFnu was positively related to performance and inversely related to the fatigue score. Thus, elevated initial HF levels could be important in the parasympathetic activity increases during taper and, hence, in swimming performance improvement.     

Effects of aerobic exercise training on 24 hr profile of heart rate variability in female athletes

BACKGROUND: The aim of this study was to investigate the effects of exercise training on autonomic regulation of heart rate under daily life conditions. METHODS: Twenty-six healthy female athletes (age 24.5 +/- 1.9 yrs) involved in regular physical activity were recruited during a period of yearly rest and randomly assigned to a five-week aerobic exercise training program (n = 13) or to a non-exercise control group (n = 13). MEASURES: Before and after the five-week training, all subjects underwent a bycicle ergometer stress test and a 24-hour dynamic ECG monitoring. Autonomic regulation of heart rate has been investigated by means of both time and frequency domain analyses of heart rate variability (HRV). Spectral analysis of R-R interval variability (autoregressive algorithm) provided markers of sympathetic (low frequency, LF, 0.10 Hz) and parasympathetic (high frequency, HF, 0.25 Hz) modulation of the sinus node. RESULTS: Trained subjects showed a reduced heart rate response to submaximal workload. Before training there was no significant difference between the two groups. After training resting heart rate did not significantly differ between trained and untrained subjects. No significant differences were observed in the different time domain indexes of heart rate variability. The day-night difference in SD and SDRR were significantly less in the trained as compared to the untrained group. Normalized LF and HF components did not significantly differ between trained and untrained subjects, during the awake period. The decrease in the LF and the increase in the HF component during nighttime were significantly less in the trained group. The LF/HF ratio was significantly decreased during the night in the untrained group whereas it was not significantly different from the awake state in the trained group. CONCLUSIONS: These findings of the relative night-time increase in LF and the decrease in the day-night difference in time domain indexes of heart rate variability suggest that, in young female athletes, exercise training is able to induce an increase in the sympathetic modulation of the sinus node which may coexist with signs of relatively reduced, or unaffected, vagal modulation.     

DHA-rich fish oil lowers heart rate during submaximal exercise in elite Australian Rules footballers

Omega-3 fatty acids (n-3) can improve cardiovascular (CV) function. This study examined the effects of n-3 on endurance performance, recovery and CV risk factors in elite Australian Rules football players. 25 players were randomised, double-blind, to 6 g/day of docosahexaenoic acid (DHA)-rich fish oil (FO; n = 12) or sunflower oil (SO; n = 13) during 5 weeks of training. At baseline erythrocyte n-3 content, resting blood pressure (BP), fasting serum triglycerides (TG) and heart rate (HR) during treadmill running at 10 km/h were assessed. Two treadmill runs (T1 and T2) to exhaustion, separated by 5 min, were then performed at the average speed for a recent 2200 m time-trial. After 5 weeks, erythrocyte n-3 increased (FO 3.8 ± 0.6%, SO 0.6 ± 0.3%; P < 0.001) while TG (FO ?0.32 ± 0.09 mmol l^?1, SO 0.08 ± 0.05 mmol l^?1; P < 0.001), diastolic BP (FO 1.3 ± 1.3 mmHg, SO 6.8 ± 1.7 mmHg; P = 0.04) and HR during submaximal exercise (FO ?7.8 ± 2.3 beats min^?1, SO ?1.9 ± 1.9 beats min^?1; P = 0.03) decreased in FO compared with SO. Time to exhaustion (TTE) during T1 increased by Week 5 (FO 10.2 ± 2.2%, SO 17.3 ± 4.3%; P < 0.001 for time). Recovery (TTE for T2 as % T1) decreased in both groups (FO, ?3.4 ± 4.5%, SO ?8.8 ± 3.9%; P = 0.05 for time). We conclude that 5 weeks of supplementation with FO improved CV function and reduced CV risk factors, but did not improve endurance performance or recovery in elite Australian Rules footballers.     

Static apnea effect on heart rate and its variability in elite breath-hold divers

BACKGROUND: The diving response includes cardiovascular adjustments known to decrease oxygen uptake and thus prolong apnea duration. As this diving response is in part characterized by a pronounced decrease in heart rate (HR), it is thought to be vagally mediated. METHODS: In five professional breath-hold divers (BHDs) and five less-trained controls (CTL), we investigated whether the diving response is in fact associated with an increase in the root mean square successive difference of the R-R intervals (RMSSD), a time-domain heart rate variability (HRV) index. HR behavior and arterial oxygen saturation (SaO2) were continuously recorded during one maximal apnea. Short-term changes in SaO2, HR, and RMSSD were calculated over the complete apnea duration. RESULTS: BHDs presented bi-phasic HR kinetics, with two HR decreases (32 +/- 17% and 20 +/- 10% of initial HR). The second HR decrease, which was concomitant to the pronounced SaO2 decrease, was also simultaneous to a marked increase in RMSSD. CTL showed only one HR decrease (50 +/- 10% of initial HR), which appeared before the concomitant SaO2 and RMSSD changes. When all subject data were combined, arterial desaturation was positively correlated with total apnea time (r = 0.87, P < 0.01). CONCLUSION: This study indicates that baroreflex stimulation and hypoxia may be involved in the bi-phasic HR response of BHDs and thus in their longer apnea duration.     

Effects of exercise load and breathing frequency on heart rate and blood pressure variability during dynamic exercise.

It is known that heart rate (HR) variability decreases with dynamic exercise, but there are only few studies on blood pressure (BP) variability with exercise loads and the effect of breathing pattern has never been investigated. Thus, we studied HR and systolic blood pressure (SBP) signals by spectral analysis (FFT), in 9 healthy subjects, at different breathing frequencies (0.15, 0.2, 0.3, 0.4, 0.5, 0.6 Hz), at rest and during 3 exercise loads (25, 50 and 75% VO2max). BP was measured with a non-invasive device (Finapres) and continuously recorded. The power spectrum of R-R period significantly decreased with exercise loads in the low frequency band (LF: 0.04-0.128 Hz) and in the high frequency band (HF: 0.128-0.65 Hz), but with breathing frequency only in the HF part of the spectrum. The power spectrum of SBP significantly increased with exercise loads in LF and HF bands, and decreased in HF band with increasing breathing frequency. R-R and SBP HF peaks were centered on breathing frequency peaks. Therefore, spectral analysis of HR and SBP confirm the withdrawal of vagal control during exercise, while mechanical effect of respiration on SBP persists. LF/HF ratio of R-R spectral components decreased with increasing load, whereas cardiovascular sympathetic activity is known to rise, suggesting that this ratio is not a good indicator of cardiovascular autonomic modulation during exercise.     

Reliability of heart rate variability measures at rest and during light exercise in children

OBJECTIVES: To investigate the reliability of heart rate variability (HRV) measures at rest and during light exercise in children. METHODS: Short term (five minute) HRV was assessed in 12 children (11-12 years of age). HRV measures were collected at rest with the children supine, breathing at 12 breaths/min, and during exercise on a cycle ergometer while exercising at 25% of peak oxygen uptake. Both resting and exercise data were collected twice from each child. RESULTS: Intraclass correlation coefficients were low to moderate for most measures with wide confidence intervals for each variable in both resting and exercise conditions. Random variation (typical error) within repeated measurements ranged from 31% to 187%. CONCLUSIONS: These preliminary findings suggest that HRV measures are unreliable at rest and during light exercise in children aged 11-12 years. Tighter control of extraneous influences is recommended.     

Lifelong physical training prevents the age-related impairment of heart rate variability and exercise capacity in elderly people

AIM: Aging is associated with a reduction on heart rate variability (HRV) and working capacity. Aim of this study was to evaluate in a group of elite master athletes the effect of a lifelong history of endurance running on HRV and exercise working capacity. METHODS: Twenty athletes (males, age 68.5+/-4.5 years) who practiced endurance running for at least 40 years, and 20 age-sex-matched control subjects with sedentary lifestyle were studied. All the participants underwent a maximal stepwise electrocardiogram (ECG) on effort (work-rate increments of 25 Watts every 2 min) and a 24-hour ECG monitoring. RESULTS: All the time domain measures of HRV and the LF and HF powers were significantly higher in elderly athletes than in sedentary subjects (P<0.001), while the LF/HF ratio was comparable between the 2 groups. Athletes exhibited significantly higher workload than controls (1610+/-489 vs 687+/-236 W, P<0.0001). Both the groups achieved, at maximum workload, similar heart rate (142+/-10 vs 138+/-18 bpm, ns), systolic blood pressure (226+/-18 vs 220+/-16 mmHg, ns), and rate-pressure product (32,596+/-2952 vs 30,838+/-3675, ns). Maximum work-rate attained in athletes was 225 W. By contrast, none of the controls reached a work-rate higher than 150 W. In the whole group we also showed a positive correlation between the time domain HRV parameter SDNN and maximum workload (r=0.58, P<0.001). CONCLUSION: Long-term endurance training induces in elderly subjects an increased HRV and a higher exercise working capacity, which are well-established predictors of cardiovascular and overall mortality.     

Exercise training and heart rate variability in older people.

PURPOSE: Heart rate variability (HRV), a characteristic that is potentially increased by physical activity, has been associated with incidence of cardiac events and total mortality. Since the incidence of cardiac events among older people is high and their physical activity levels and HRV are generally low, it is important to investigate whether regular physical activity can modify HRV in this age group. The purpose of the study was to investigate the effect of regular physical activity on HRV in older men and women. METHODS: In a randomized controlled trial, the effect of six months' training on HRV was investigated in a group of 51 older men and women (67.0 +/- 5.1 yr). The training group gathered three times per week for 45 min supervised training. RESULTS: At the end of the intervention period, HRV was higher primarily during the day. During daytime, the SD of all normal intervals (+6%) as well as the low frequency component (+ 15%) and the very low frequency component (+ 10%) of HRV were significantly increased (P < 0.05) as compared with the control group. Effects of training were most pronounced in subjects inactive in sports at baseline. CONCLUSION: This study demonstrates that regular physical activity increases HRV (specifically in the very low and low frequency components) in older subjects. Hence, in older subjects, physical training may be an effective means to modify positively a factor that is associated with increased incidence of cardiac events.     

Relation between heart rate variability and training load in middle-distance runners

PURPOSE: Monitoring physical performance is of major importance in competitive sports. Indices commonly used, like resting heart rate, VO2max, and hormones, cannot be easily used because of difficulties in routine use, of variations too small to be reliable, or of technical challenges in acquiring the data. METHODS: We chose to assess autonomic nervous system activity using heart rate variability in seven middle-distance runners, aged 24.6 +/- 4.8 yr, during their usual training cycle composed of 3 wk of heavy training periods, followed by a relative resting week. The electrocardiogram was recorded overnight twice a week and temporal and frequency indices of heart rate variability, using Fourier and Wavelet transforms, were calculated. Daily training loads and fatigue sensations were estimated with a questionnaire. Similar recordings were performed in a sedentary control group. RESULTS: The results demonstrated a significant and progressive decrease in parasympathetic indices of up to -41% (P < 0.05) during the 3 wk of heavy training, followed by a significant increase during the relative resting week of up to +46% (P < 0.05). The indices of sympathetic activity followed the opposite trend, first up to +31% and then -24% (P < 0.05), respectively. The percentage increasing mean nocturnal heart rate variation remained below 12% (P < 0.05). There was no significant variation in the control group. CONCLUSION: This study confirmed that heavy training shifted the cardiac autonomic balance toward a predominance of the sympathetic over the parasympathetic drive. When recorded during the night, heart rate variability appeared to be a better tool than resting heart rate to evaluate cumulated physical fatigue, as it magnified the induced changes in autonomic nervous system activity. These results could be of interest for optimizing individual training profiles.     

Effects of resistance training of moderate intensity on heart rate variability,body composition,and muscle strength in healthy elderly women

Purpose

The practice of resistance training is recommended as non-pharmacological strategy during aging. In this study, we propose training composed of exercises, leg 180° press, seated row, leg curl, bench press, abduction machine, push down, adduction machine, and curl biceps. Accordingly, this study aimed to determine the effects of dynamic resistance training on autonomic response, muscle strength, and body composition of elderly women without comorbidities.

Methods

Twenty-six healthy older women (65 ± 3 years) were randomly divided into two groups. The Control Group (CG) consisted of 13 subjects not engaged in any physical exercise, while the Training Group (GT) (n = 13) performed 8 strength training exercises with 3 sets of 8 maximum repetitions. Heart rate variability, body composition, and muscle strength were assessed before and after the 12 weeks in both groups.

Results

No significant difference was found in body composition, muscle strength, and heart rate variability between CG and TG before (baseline) 12 weeks of training. Significant differences between pre- and post-training moments were found only in training group. In this sense, results demonstrated improvement (p < 0.05) in body fat mass (23.0 ± 1.2 vs. 20.0 ± 1.1 kg), fat-free mass (38.0 ± 1.5 vs. 42.0 ± 1.4 kg), strength of upper (17.8 ± 1.0 vs. 22.2 ± 1.1 kgf) and lower limbs (27.1 ± 2.4 vs. 34.1 ± 2.5 kgf), and in time and frequency domain measures of heart rate variability, highlighting the indices LF/HF (1.2 ± 0.4 vs. 0.7 ± 0.1).

Conclusions

The dynamic resistance training protocol presented in this study may be regarded as an effective approach to prevent cardiovascular morbidity and mortality in elderly women.

     

Effect of training status and relative exercise intensity on physiological responses in men

PURPOSE: This study examined the effect of training status and relative exercise intensity on physiological responses to endurance exercise in humans. METHODS: Seven endurance trained (TR: peak oxygen uptake [VO2peak] = 65.8 +/- 2.4 mL x kg(-1) min(-1)) and six untrained (UT: VO2peak = 46.2 +/- 1.9 mL x kg(-1) x min(-1)) men cycled for 60 min, either at a work rate corresponding to approximately 70% VO2peak or approximately 95% lactate threshold (LT). RESULTS: The work rate and relative exercise intensity (i.e., % VO2peak) for UT 95% LT were lower (P < 0.01) than for all of the other trials. Although the work rate for UT 70% VO2peak was lower (P < 0.001) than for TR 70% VO2peak and TR 95% LT, average heart rate (HR) for the trial was higher (P < 0.01) throughout exercise in UT 70% VO2peak compared with all of the other trials. Plasma lactate and ammonia concentrations were greater (P < 0.01) during exercise in UT 70% VO2peak compared with all of the other trials. There was a tendency (P = 0.077) for plasma hypoxanthine to be greater at 60 min in UT 70% VO2peak compared with the other trials. At no time were any of the plasma metabolite concentrations different between the UT 95% LT, TR 95% LT and TR 70% VO2peak trials. CONCLUSIONS: These data demonstrate that HR and plasma markers of metabolic stress were greater in UT compared with TR when exercise was performed at 70% VO2peak but were similar during exercise at 95% LT.