Abstract
Post-exercise hypotension (PEH), calculated by the difference between post and pre-exercise values, it is greater after exercise performed in the evening than the morning. However, the hypotensive effect of morning exercise may be masked by the morning circadian increase in blood pressure. This study investigated PEH and its hemodynamic and autonomic mechanisms after sessions of aerobic exercise performed in the morning and evening, controlling for responses observed after control sessions performed at the same times of day. Sixteen pre-hypertensive men underwent four sessions (random order): two conducted in the morning (7:30am) and two in the evening (5pm). At each time of day, subjects underwent an exercise (cycling, 45 min, 50%VO2peak) and a control (sitting rest) session. Measurements were taken pre- and post-interventions in all the sessions. The net effects of exercise were calculated for each time of day by [(post-pre exercise)-(post-pre control)] and were compared by paired t-test (P<0.05). Exercise hypotensive net effects (e.g., decreasing systolic, diastolic and mean blood pressure) occurred at both times of day, but systolic blood pressure reductions were greater after morning exercise (-7±3 vs. -3±4 mmHg, P<0.05). Exercise decreased cardiac output only in the morning (-460±771 ml/min, P<0.05), while it decreased stroke volume similarly at both times of day and increased heart rate less in the morning than in the evening (+7±5 vs. +10±5 bpm, P<0.05). Only evening exercise increased sympathovagal balance (+1.5±1.6, P<0.05) and calf blood flow responses to reactive hyperemia (+120±179 vs. -70±188 U, P<0.05). In conclusion, PEH occurs after exercise conducted at both times of day, but the systolic hypotensive effect is greater after morning exercise when circadian variations are considered. This greater effect is accompanied by a reduction of cardiac output due to a smaller increase in heart rate and cardiac sympathovagal balance.
Highlights
Aerobic training decreases systolic/diastolic blood pressure (BP) in normotensive, pre-hypertensive and hypertensive individuals [1]
The main finding of this study is that, aerobic exercise conducted both in the morning and evening produced post-exercise hypotension (PEH), the hypotensive effect of exercise was greater for systolic BP after morning exercise when circadian variations of BP were taken into account
This greater morning systolic PEH occurred due to a decrease in cardiac output (CO) secondary to a blunted increase in heart rate (HR), which was mediated by a lower sympathovagal balance increase after exercising at this time of day
Summary
Aerobic training decreases systolic/diastolic blood pressure (BP) in normotensive, pre-hypertensive and hypertensive individuals [1]. A single session of aerobic exercise produces post-exercise hypotension (PEH), i.e. a clinically relevant decrease in BP after exercise [2]. Previous studies [5,6,7,8] that calculated PEH as post-pre values and compared morning and afternoon exercise, reported PEH only after exercise conducted in the afternoon, suggesting that morning exercise has no hypotensive effect. Exercise may have the same or even a greater hypotensive effect in the morning, but that effect may have been masked by the morning circadian rise in BP. This effect can be detected if an appropriate time control condition is included in the experimental design. The first objective of this study was to compare the magnitude of PEH after exercise sessions performed in the morning and evening, controlling for circadian changes observed in control sessions (no exercise) executed at the same times of day
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