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Morning Versus Evening Aerobic Training Effects on BP in Treated HTN
Study Questions:
Are the hypotensive effects of aerobic training in hypertensive people greater when exercise is performed in the evening versus the morning?
Methods:
A total of 50 sedentary men with medication-controlled hypertension was randomized into 3 intervention groups: morning aerobic training (MT), evening aerobic training (ET), and control. The MT and ET groups participated in progressive cycle ergometer exercise at moderate intensity, up to 45 minutes per session, and the control group engaged in stretching exercises for 30 minutes, half the participants in the morning and half in the evening. All groups participated in 3 sessions per week for 10 weeks. Pre- and post-intervention measurements included clinic and ambulatory blood pressure (BP), heart rate (HR), electrocardiogram, and other hemodynamic parameters such as cardiac output (CO) (by Ficke method) and stroke volume (CO/HR). Also, indices of autonomic modulation, such as low- and high-frequency components of HR variability (cardiac sympathovagal balance), total variance of systolic BP, and cardiac baroreflex sensitivity, were calculated before and after the 10 weeks by spectral analysis of HR and BP.
Results:
The groups were comparable in age, anthropometrics, baseline BPs, chronotypes, and types of antihypertensive medications. As expected, exercise capacity increased in both aerobically trained groups. There was no change in weight in any group. Clinic systolic BP decreased in ET only, differently from MT and control, at both morning (-5 ± 6) and evening (-8 ± 7) assessments. Ambulatory systolic and diastolic BP were unchanged in all 3 groups. However, asleep diastolic (-3 ± 4) and 24-hr BP (-3 ± 5) decreased in ET only, differently from MT and control. CO did not change in any group, whereas stroke volume increased and systemic vascular resistance (SVR) decreased in ET only compared with control. Resting HR decreased in both MT and ET compared with control. Both ET and MT decreased vasomotor sympathetic modulation and increased baroreflex sensitivity compared with control, with greater changes in ET compared with MT.
Conclusions:
In medication-controlled hypertensive men, aerobic training in the evening reduced clinic and ambulatory BP due to decreased SVR and vasomotor sympathetic modulation. Aerobic training performed in either morning or evening reduces SVR and increases baroreflex sensitivity, though effects are greater with ET.
Perspective:
Aerobic training any time of day is beneficial, especially for people with hypertension. However, for hypertensive men the benefits may be greater with evening training, though this may not apply to women. The hypotensive effects of exercise are greater with higher BPs, so morning dosing of antihypertensive medications may attenuate hypotensive effects of MT. Perhaps most importantly, previous research has demonstrated an 8% reduction for stroke risk and 5% reduction for coronary artery disease risk with a mere 3 mmHg decrease in clinic systolic BP, so the results seen with ET in this study have beneficial morbidity and mortality implications.
Keywords: Hypertension, Antihypertensive Agents, Exercise, Heart Rate, Blood Pressure, Blood Pressure Monitoring, Ambulatory, Baroreflex, Stroke Volume, Cardiac Output, Vascular Resistance, Electrocardiography
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