Abstract
IntroductionPrevious studies observed diurnal variation in hemodynamic responses during recovery from whole-body exercise, with vasodilation appearing greater after evening versus morning sessions. It is unclear what mechanism(s) underlie this response. Since small muscle-mass exercise can isolate peripheral effects related to postexercise vasodilation, it may provide insight into possible mechanisms behind this diurnal variation.MethodsThe study was conducted in ten healthy (5F, 5M) young individuals, following single-leg dynamic knee-extension exercise performed in the Morning (7:30–11:30 am) or the Evening (5–9 pm) on two different days, in random order. Arterial pressure (automated auscultation) and leg blood flow (femoral artery Doppler ultrasound) were measured pre-exercise and during 120 min postexercise. Net effect for each session was calculated as percent change in blood flow (or vascular conductance) between the Active Leg and the Inactive Leg.ResultsFollowing Morning exercise, blood flow was 34.9 ± 8.9% higher in the Active Leg versus the Inactive Leg (p < 0.05) across recovery. Following Evening exercise, blood flow was 35.0 ± 8.8% higher in the Active Leg versus the Inactive Leg (p < 0.05). Likewise, vascular conductance was higher in the Active Leg versus the Inactive Leg (Morning: +35.1 ± 9.0%, p < 0.05; Evening: +33.2 ± 8.2%, p < 0.05). Morning and Evening blood flow (p = 0.66) and vascular conductance (p = 0.64) did not differ.ConclusionThese data suggest previous studies which identified diurnal variations in postexercise vasodilation responses are likely reflecting central rather than peripheral modulation of cardiovascular responses.
Highlights
Previous studies observed diurnal variation in hemodynamic responses during recovery from whole-body exercise, with vasodilation appearing greater after evening versus morning sessions
Vascular conductance was higher in the Active Leg versus the Inactive Leg (Morning: +35.1 ± 9.0%, p < 0.05; Evening: +33.2 ± 8.2%, p < 0.05)
Flow-mediated dilation was blunted following afternoon exercise but unchanged following morning exercise (Jones et al, 2010). These initial observations are consistent with diurnal variation in exercise responses, but difficult to interpret as vascular responses to whole-body exercise are regulated by multiple mechanisms, such as baroreflex resetting (Halliwill et al, 1996b), sympathoinhibition (Halliwill et al, 1996a; Forjaz et al, 1999), and histamine dependentvasodilation (Lockwood et al, 2005b; McCord and Halliwill, 2006; Romero et al, 2015; Ely et al, 2017)
Summary
Previous studies observed diurnal variation in hemodynamic responses during recovery from whole-body exercise, with vasodilation appearing greater after evening versus morning sessions. This information may contribute to understand the vascular response to a stimulus at different times of day, which may guide therapy strategies or administration of medications Along these lines, we have previously shown that a standardized small muscle-mass exercise protocol using single-leg dynamic knee-extension is an effective model to test for changes in local blood flow and vascular conductance in response to exercise (Barrett-O’Keefe et al, 2013; Romero et al, 2015), and might be sensitive to detect diurnal variation in the histaminergic component of sustained postexercise vasodilation
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