Dose-response relationship of endurance training for autonomic circulatory control in healthy seniors
ABSTRACT Aging results in marked abnormalities of cardiovascular regulation. Regular exercise can improve many of these age-related abnormalities. However, it remains unclear how much exercise is optimal to achieve this improvement or whether the elderly can ever improve autonomic control by exercise training to a degree similar to that observed in healthy young individuals. Ten healthy sedentary seniors [71 +/- 3 (SD) yr] trained for 12 mo; training involved progressive increases in volume and intensity. Static hemodynamics were measured, and R-wave-R-wave interval (RRI), beat-to-beat blood pressure (BP) variability, and transfer function gain between systolic BP and RRI were calculated at baseline and every 3 mo during training. Data were compared with those obtained in 12 Masters athletes (68 +/- 3 yr) and 11 healthy sedentary young individuals (29 +/- 6 yr) at baseline. Additionally, the adaptation of these variables after completion of identical training loads was compared between the seniors and the young. Indexes of RRI variability and baroreflex gain were decreased in the sedentary seniors but preserved in the Masters athletes compared with the young at baseline. With training in the seniors, baroreflex gain and resting BP showed a peak adaptation after moderate doses of training following 3-6 mo. Indexes of RRI variability continued to improve with increasing doses of training and increased to the same magnitude as the young at baseline after heavy doses of training for 12 mo; however, baroreflex gain never achieved values equivalent to the young at baseline, even after a year of training. The magnitude of the adaptation of these variables to identical training loads was similar (no interaction effects of age x training) between the seniors and the young. Thus RRI variability in seniors improves with increasing "dose" of exercise over 1 yr of training. In contrast, more moderate doses of training for 3-6 mo may optimally improve baroreflex sensitivity, associated with a modest hypotensive effect; however, higher doses of training do not lead to greater enhancement of these changes. Seniors retain a similar degree of "trainability" as young subjects for cardiac autonomic function to dynamic exercise.
- SourceAvailable from: Mark Rakobowchuk
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- "Alternatively, Goldstein and colleagues (Goldstein et al. 2011; Rahman et al. 2011) suggest LF power reflects baroreflex function and cardiac autonomic modulation by these sensory neurones (Rahman et al. 2011). Young apparently healthy (Iwasaki et al. 2003; Komine et al. 2009) and older participants (Monahan et al. 2001; Okazaki et al. 2005) display improved baroreflex function with training and our observation of increased absolute LF power complements this work. Whether a greater dose of interval exercise that induces high metabolic stress eventually causes an unfavourable regulation of HRV and baroreflex as noted in athletes (Iellamo et al. 2002) requires detailed study. "
ABSTRACT: Traditional continuous aerobic exercise training attenuates age-related increases of arterial stiffness, however, training studies have not determined whether metabolic stress impacts these favourable effects. Twenty untrained healthy participants (n = 11 heavy metabolic stress interval training, n = 9 moderate metabolic stress interval training) completed 6 weeks of moderate or heavy intensity interval training matched for total work and exercise duration. Carotid artery stiffness, blood pressure contour analysis, and linear and non-linear heart rate variability were assessed before and following training. Overall, carotid arterial stiffness was reduced (p < 0.01), but metabolic stress-specific alterations were not apparent. There was a trend for increased absolute high-frequency (HF) power (p = 0.10) whereas both absolute low-frequency (LF) power (p = 0.05) and overall power (p = 0.02) were increased to a similar degree following both training programmes. Non-linear heart rate dynamics such as detrended fluctuation analysis [Formula: see text] also improved (p > 0.05). This study demonstrates the effectiveness of interval training at improving arterial stiffness and autonomic function, however, the metabolic stress was not a mediator of this effect. In addition, these changes were also independent of improvements in aerobic capacity, which were only induced by training that involved a high metabolic stress.Arbeitsphysiologie 09/2012; 113(4). DOI:10.1007/s00421-012-2486-6 · 2.30 Impact Factor
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- "Recent studies in rats have shown that aerobic training, either through swimming exercises (Souza et al., 2009) or motorized treadmill (Rossi et al, 2009), promoted a decrease in LF oscillations and an increase in HF oscillations, thus suggesting a reduction in the cardiac sympathetic influence and the augmentation of the cardiac vagal influence. In human beings, similar results were found after an aerobic physical training program, both in healthy (Sloan et al., 2009; Okazaki et al., 2005) and hypertensive individuals (Pagkalos et al., 2008). However, none of the studies, either experimental or clinical, has compared the influence of the daily duration of aerobic physical training on cardiac autonomic adaptations in different approaches evaluated. "
ABSTRACT: The present study has investigated in conscious rats the influence of the duration of physical training sessions on cardiac autonomic adaptations by using different approaches; 1) double blockade with methylatropine and propranolol; 2) the baroreflex sensitivity evaluated by alternating bolus injections of phenylephrine and sodium nitroprusside; and 3) the autonomic modulation of HRV in the frequency domain by means of spectral analysis. The animals were divided into four groups: one sedentary group and three training groups submitted to physical exercise (swimming) for 15, 30, and 60min a day during 10 weeks. All training groups showed similar reduction in intrinsic heart rate (IHR) after double blockade with methylatropine and propranolol. However, only 30-min and 60-min physical training presented an increase in the vagal autonomic component for determination of basal heart rate (HR) in relation to group sedentary. Spectral analysis of HR showed that the 30-min and 60-min physical training presented the reduction in low-frequency oscillations (LF=0.20-0.75Hz) and the increase in high-frequency oscillations (HF=0.75-2.5Hz) in normalized units. These both groups only showed an increased baroreflex sensitivity to tachycardiac responses in relation to group sedentary, however when compared, the physical training of 30-min exhibited a greater gain. In conclusion, cardiac autonomic adaptations, characterised by the increased predominance of the vagal autonomic component, were not proportional to the duration of daily physical training sessions. In fact, 30-minute training sessions provided similar cardiac autonomic adaptations, or even more enhanced ones, as in the case of baroreflex sensitivity compared to 60-minute training sessions.Autonomic neuroscience: basic & clinical 01/2011; 159(1-2):32-7. DOI:10.1016/j.autneu.2010.07.006 · 1.37 Impact Factor
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- "Heart rate variability measures showed no dose– response between the more fit groups in our study and other cross-sectional data show a negative dose– response (Buchheit et al., 2005, 2006). Longitudinal studies have shown that 3 months of moderate exercise is sufficient to increase heart rate variability indices and that longer-term, more intense training results in no further gains (Iwasaki, Zhang, Zuckerman , & Levine, 2003; Okazaki et al., 2005). The lack of a dose–response between exercise levels and heart rate variability indices appears to be a reproducible physiological phenomenon. "
ABSTRACT: Heart rate variability estimates cardiac autonomic modulation, but the relationship between habitual physical activity and heart rate variability remains unclear. The aims of this study were to compare RR-interval and heart rate variability indices in individuals of different habitual physical activity levels, and examine the relationship between habitual physical activity and heart rate variability. Ninety-two healthy volunteers (47 men, 45 women; mean age 23.1 years, s = 2.1) were divided into tertiles according to the Baecke Questionnaire score. Standard heart rate variability indices were derived from 5-min resting RR-interval recordings with paced respiration (0.25 Hz). Between-group differences and the relationship between habitual physical activity and heart rate variability were assessed. More active participants (tertiles 2-3) had longer RR-intervals than those in tertile 1 (P < 0.05). Participants in tertile 2 had higher root mean squared differences of successive normal RR-intervals than those in tertile 1 and a higher standard deviation of normal RR-intervals than those in tertiles 1 and 3. There was a positive linear relationship between habitual activity and RR-interval. Differing RR-interval lengths were found in subgroups of young individuals according to level of habitual physical activity. More active individuals showed resting bradycardia without evidence of enhanced cardiac parasympathetic modulation. The mechanism linking habitual physical activity and RR-interval length appears to be independent of physiological mechanisms that can be measured by heart rate variability.Journal of Sports Sciences 08/2008; 26(11):1171-7. DOI:10.1080/02640410802004930 · 2.10 Impact Factor