Effects of aerobic training on heart rate dynamics in sedentary subjects.

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

Heart rate dynamics after combined endurance and strength training in older men.

PURPOSE: Aging alters cardiac autonomic function, which may contribute to a higher risk of cardiac events. Spectral measures of HR variability (HRV) and fractal-like behavior of HR are considered as markers of a healthy heart. The present study examined the effects of combining endurance and strength training compared with endurance or strength training alone on HR dynamics and physical fitness in older previously untrained men aged 40-67 yr. METHODS: Subjects were randomized into endurance training (E, n = 23), strength training (S, n = 25), combined endurance and strength training (ES, n = 29), or control group (C, n = 16). Short-term fractal scaling exponent (alpha1) and spectral HRV were analyzed from maximal aerobic cycling tests and during supine rest, and leg extension one repetition maximum strength was measured. RESULTS: Aerobic capacity and maximal strength increased in the training groups performing endurance and/or strength training, respectively. Only ES showed a decrease after training in fractal HR behavior during exercise, and the difference was significant between groups (P = 0.019). During supine rest, alpha1 only decreased significantly (P = 0.039) in ES from 1.18 (SD = 0.20) to 1.11 (SD = 0.21). The decrease in alpha1 at rest from 1.21 (SD = 0.19) to 1.11 (SD = 0.22) also approached significance (P = 0.061) in E. Changes in spectral measures of HRV were minor during the study period and only occurred during exercise. CONCLUSION: Fractal HR dynamics were improved more by combining strength training with endurance training in our older men compared with endurance training alone, although strength training alone produced no changes in fractal HR behavior. The synergistic effect in fractal HR behavior occurred regardless of changes in aerobic capacity.

Estimation of maximal heart rate using the relationship between heart rate variability and exercise intensity in 40-67 years old men.

Large interindividual variation in maximal heart rate (HRmax) may not be accounted for by age alone. In order to evaluate a novel method in the prediction of HRmax, this study examined the profile of HR variability (HRV) during exercise in 40-67 years old men (n = 74). R-R intervals were recorded during supine rest and during a graded exercise test by cycle ergometry until exhaustion. A third-degree polynomial function was fitted to the HRV data recorded during exercise to represent the HRV profile of each subject. The instantaneous beat-to-beat R-R interval variability (SD1), high (HF) and low frequency power decreased between all consecutive exercise intensities (P < 0.033). The relationship between HRmax and a variable illustrating the declining rate of HF (HRHF50%) was stronger (r = 0.50, P < 0.001) than between HRmax and age (r = -0.36, P < 0.01). The regression analysis showed that a more accurate estimation of HR(max) was attained when HRV was used in the equation in addition to age: HRmax = 160.633-0.603(age) + 0.441(HRHF50%) (SEE = 9.8 bpm vs. 11.6 bpm in the equation based on age alone). The decline of HRV during incremental exercise seems to be useful for accurate estimation of maximal heart rate.

Heart rate dynamics after controlled training followed by a home-based exercise program.

Daily aerobic training results in autonomic control of the heart toward vagal dominance. The constancy of vagal dominance after controlled training followed by a home-based training program in accordance with contemporary guidelines is not known. We set out here to study whether the vagal dominance induced by 8 weeks of controlled aerobic training is preserved after a 10-month home-based training program. For the controlled study, healthy men were randomized as training (n=18) and control subjects (n=6). The training was started by a supervised 8-week period with six training sessions a week [45 (15) min each] at an intensity of 70-80% of maximum heart rate, followed by a home-based training program for 10 months in accordance with the American College of Sports Medicine recommendations. Cardiovascular autonomic function was assessed by analyzing HR variability over a 24-h period and separately during the night hours (midnight-6 a.m.). Maximal running performance improved during the controlled training 16 (7)% (range 4-31%, P<0.001) and remained 8 (8)% (range -3 to 23%, P<0.001) above the baseline level after the home-based training program. At night, the vagally mediated high-frequency (HF) power of R-R intervals increased during the controlled training from 6.7 (1.3) to 7.3 (1.1) ln ms2 ( P<0.001) and remained higher than the baseline after the home-based training [7.0 (1.3) ln ms2, P<0.05]. The changes in running performance correlated with the changes in HF power at night (r=0.41, P<0.05) and over 24 h (r=0.44, P<0.05) after the home-based training program. Similarly, the changes in body mass index correlated with the changes in HF power over 24 h (r=-0.44, P<0.05) after the home-based training program. The high vagal outflow to the heart after the home-based training is associated with good physical performance and body mass control.

Cardiovascular autonomic function correlates with the response to aerobic training in healthy sedentary subjects.

Individual responses to aerobic training vary from almost none to a 40% increase in aerobic fitness in sedentary subjects. The reasons for these differences in the training response are not well known. We hypothesized that baseline cardiovascular autonomic function may influence the training response. The study population included sedentary male subjects (n = 39, 35 +/- 9 yr). The training period was 8 wk, including 6 sessions/wk at an intensity of 70-80% of the maximum heart rate for 30-60 min/session. Cardiovascular autonomic function was assessed by measuring the power spectral indexes of heart rate variability from 24-h R-R interval recordings before the training period. Mean peak O2 uptake increased by 11 +/- 5% during the training period (range 2-19%). The training response correlated with age (r = -0.39, P = 0.007) and with the values of the high-frequency (HF) spectral component of R-R intervals (HF power) analyzed over the 24-h recording (r = 0.46, P = 0.002) or separately during the daytime hours (r = 0.35, P = 0.028) and most strongly during the nighttime hours (r = 0.52, P = 0.001). After adjustment for age, HF power was still associated with the training response (e.g., P = 0.001 analyzed during nighttime hours). These data show that cardiovascular autonomic function is an important determinant of the response to aerobic training among sedentary men. High vagal activity at baseline is associated with the improvement in aerobic power caused by aerobic exercise training in healthy sedentary subjects.