Following Evening exercise, blood flow was Conclusion: These data suggest previous studies which identified diurnal variations in postexercise vasodilation responses are likely reflecting central rather than peripheral modulation of cardiovascular responses.
Blood flow and vascular conductance remain elevated up to 2 h after an acute session of aerobic exercise Halliwill et al. This sustained postexercise vasodilation of skeletal muscle vascular beds has been observed after both whole-body exercise e.
Depending on the form of exercise, the underlying mechanisms of sustained postexercise vasodilation can differ. For example, after small muscle-mass exercise histamine is produced and released in the active skeletal muscles and induces vasodilation through interaction with histamine H 1 - and H 2 -receptors McCord and Halliwill, ; Ely et al. Whereas in whole-body exercise, postexercise reductions in sympathetic nerve activity further contributes to this histaminergic vasodilation Halliwill et al.
As most aspects of cardiovascular regulation demonstrate a circadian or diurnal pattern Portaluppi and Hermida, , it is possible the mechanisms that drive sustained postexercise hypotension are impacted by time of day. Circadian variation promotes lower levels of sympathetic activity Grassi et al. Additionally, a greater reactive hyperemia response and fall in total vascular resistance was observed after whole-body exercise in the evening than in the morning de Brito et al.
In contrast, flow-mediated dilation was blunted following afternoon exercise but unchanged following morning exercise Jones et al. 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.
Thus, isolating one of these mechanisms would help to further elucidate which avenues diurnal variation may act through to influence the vascular response to exercise.
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. Therefore, the aim of this study was to compare leg blood flow and vascular conductance after a 1 h session of single-leg dynamic knee-extension exercise, performed in the morning and in the evening. Our hypothesis was that leg blood flow and vascular conductance would be higher after exercise in both the morning and the evening, unchanged in the control non-active leg, and that this rise in blood flow and vascular conductance would be greater after evening, compared to morning exercise.
Ten young healthy non-smoking subjects 5 females, 5 males volunteered for the current study. All subjects were deemed sedentary or recreationally active based on their exercise habits in the previous 12 months as assessed by two self-reported questionnaires Baecke et al.
Females were not pregnant as confirmed by a negative pregnancy test before every study visit. No subjects were taking over-the-counter or prescription medications at the time of the study, with the exception of oral contraceptives. Female subjects were investigated during the early follicular phase of their menstrual cycle. All subjects signed the informed consent prior to participation and the study was conducted in accordance with the latest revision of the Declaration of Helsinki, and was not registered in a database.
Leg blood flow was assessed by duplex ultrasonography using a linear-array ultrasound transducer L probe, Philips iE33, Andover, MA, United States to identify possible anatomical difficulties and to familiarize subjects with the procedure. All subjects underwent a peak single-leg dynamic knee-extension exercise test to volitional fatigue to determine the work rate for the study days.
Workload was increased 3 W every minute until the subject could not keep up the required cadence or range of motion. This exercise model produced volitional fatigue in 6. Subjects reported to the laboratory on two study days, one in the Morning — am. Conditions were randomized and separated by 3 to 7 days. Subjects were instructed to keep similar routines and to abstain from alcohol, caffeine, and exercise for 24 h before each experiment.
Subjects were also required to arrive at the laboratory having fasted for at least the previous 4 h. The testing area had no windows; therefore, luminosity was kept the same for all experimental sessions. After arriving at the laboratory, subjects rested in the supine position for 10 min before the start of measurements. Leg blood flow in each leg and arterial pressure were measured twice 30 min before exercise, and every 20 min during the min after exercise.
Power output was recorded continuously throughout the 60 min dynamic knee-extension exercise. All hemodynamic measurements were performed with subjects remaining quiet and relaxed in the supine position. Heart rate and arterial pressure were recorded in triplicate before every leg blood flow measurement. Hokanson, Inc. Custom ultrasound software was used to capture the forward and reverse Doppler-shifted signals from the ultrasound system.
Recordings were subsequently analyzed with an intensity-weighted algorithm to determine mean blood velocity following standard methods for quantification Buck et al. Velocity measurements were assessed at an average depth of 1. Average femoral artery diameter was determined by automated edge-detection software Vascular Research Tools 5 — Version 6. The normal distribution of data was confirmed by Shapiro—Wilk test.
The average of measurements taken prior to exercise was defined as baseline for heart rate, arterial pressures, leg blood flow, and leg vascular conductance. We used a two-way for heart rate and arterial pressures or three-way for leg blood flow and leg vascular conductance repeated-measures ANOVA with a priori contrasts to analyze differences in session Morning vs. Evening , condition Active Leg vs. Inactive Leg , and time Pre vs.
This approach allowed examination of both linear and quadratic relationships across time, and tested whether or not the relationships differed between the sessions, as demonstrated previously Romero et al. Subjects matched a physical activity level corresponding to recreationally active. No subject was classified as an extreme chronotype, as 1 was classified as E-type favor eveningness , 4 as M-type favor morningness , and 5 were intermediate not favoring either chronotype.
Pre-exercise mean arterial pressure and heart rate were similar between morning and evening experimental sessions, as shown in Table 2. Table 2. Central hemodynamics pre- and post-exercise performed in the morning and the evening. While exercising, heart rate Morning: Evening: Table 2 shows heart rate and mean arterial pressure pre-exercise and during recovery from exercise.
Figure 1 shows leg blood flow and leg vascular conductance pre-exercise and during recovery from exercise, comparing the Active Leg to the Inactive Leg during recovery from exercise in the Morning and Evening. Figure 1. Leg blood flow upper panels and leg vascular conductance lower panels pre-exercise and during min of recovery from exercise in Morning left panels or Evening right panels sessions, showing both the response in the Active Leg and the Inactive Leg.
Prior to exercise, blood flow and vascular conductance did not differ between Active Leg and Inactive Leg or between Morning and Evening sessions. Following Morning exercise, blood flow was Figure 2 depicts how these net effects the percent change in blood flow or vascular conductance between the Active Leg and the Inactive Leg referenced to the pre-exercise values for both legs vary across the 2-h time-course of recovery, as well as how they compare between the Morning and Evening sessions.
Figure 2. Measurements were performed at baseline, and then at 3 hr, 24 hr, 72 hr, and 7 days postwounding. At 3 hr, flow at the center of the back wound had increased to Flow at the perimeter of the back wound rose as well, but not as high as at wound center, to twice the baseline level 4.
Flow values at control sites on the back did not increase from baseline. Flow at the center of the paw wound rose from 7. There was only a very small increase in the basal temperature wound response at the paw perimeter.
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