Evening but Not Morning Aerobic-Training Improves Sympathetic Nerve Activity and Sympathetic Baroreflex Sensitivity in Treated Hypertension: A Randomized Clinical Trial

Background: A previous study demonstrated that the blood pressure (BP)-lowering effect is potentiated when aerobic exercise training is conducted in the evening than in the morning in medicated people with hypertension. Additionally, this greater reduction in BP occurred concomitantly with a greater decrease in sympathetic vasomotor modulation evaluated by BP variability, which suggests a greater effect of evening training on sympathetic autonomic regulation. However, this hypothesis still needs to be using direct measures. Objective: To compare the effect of 10 weeks of aerobic training conducted in the morning (MT) with the same training conducted in the evening (ET) on muscle sympathetic nerve activity (MSNA) and sympathetic baroreflex sensitivity (BRS) in treated hypertension. Methods: This randomized clinical trial was conducted in a single-center with a parallel-group design. Twenty-three older patients with treated hypertension (12 males, 67±6 y) were randomly allocated into training in the MT group (7-10 AM) (n=12) or in the ET group (5-8 PM) (n=11). The aerobic training consisted of cycling 3 times/week for 45 min at moderate intensity. Before and after 10 weeks of training, sympathetic BRS was evaluated across the extensive range of the reflex arc by eliciting rapid changes in BP induced by sequential bolus injections of nitroprusside for 1 min followed by phenylephrine for 2 min (modified-Oxford technique). We continuously record beat-to-beat BP (finger photoplethysmography), heart rate (electrocardiography), and MSNA (fibular nerve microneurography). Sympathetic BRS was quantified the weighted negative linear regression slope between diastolic BP (3 mmHg bin) and MSNA burst incidence [(bursts/100 heartbeats)/mmHg]. Two-way mixed ANOVAs were employed with significance set as P≤0.05. Results: Systolic BP decreased after ET but not after MT (-13 [95% CI = -25 to -2] vs. -1 [95% CI = -8 to +6] mmHg, P=0.04), respectively, while diastolic BP decreased similarly in both groups. MSNA incidence decreased greater after ET than MT (-12 [95% CI = -16 to -9] vs. -3 [95% CI = -10 to +4] bursts/100bpm, P=0.01). Sympathetic BRS improved only after ET but not after MT (-0.8 [95% CI = -1.3 to -0.3] vs. 0 [95% CI = -0.7 to +0.7] bursts/100bpm/mmHg, P=0.01). Conclusion: In older adults with hypertension receiving antihypertensive medication, 10 weeks of aerobic training conducted at both times of day decreases diastolic BP while only the aerobic training conducted in the evening improves systolic BP, MSNA incidence, and sympathetic BRS. FAPESP: 2018/05226-0; CNPQ 304436/2018-6; OHSU Fellowship for Diversity in Research. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.