Time-of-Day-Dependent Effects of Aerobic Exercise on Carotid Hemodynamics in Sedentary Adults

Abstract

Aerobic exercise (AE) modulates vascular function through hemodynamic responses, thereby influencing cardiovascular health and risk, with the circadian rhythm system playing a crucial role. This chronobiological study investigated diurnal variations in exercise-induced hemodynamic changes in the common carotid artery. In a randomized crossover trial, twenty-two sedentary adults completed eight AE interventions (one per laboratory visit day), with each session performed at one of eight evenly distributed time points (from 06:00 to 20:00). Vascular ultrasound imaging and hemodynamic parameter calculations were performed both pre- and post-exercise. Compared to other time points, AE at 06:00 and 18:00 induced a greater and more sustained increase in mean flow rate and wall shear stress (WSS). Moreover, AE at 06:00 was associated with a smaller increase in oscillatory shear index and a larger decrease in peripheral resistance compared to other time points. Exercise-induced hemodynamic responses exhibited significant temporal variations. These findings emphasize the importance of exercise timing in optimizing vascular benefits for sedentary individuals.

Keywords: aerobic exercise; circadian rhythm; exercise timing; hemodynamics; vascular health.

Figure 1

The experimental protocol for each aerobic exercise (AE) session. Each participant completed eight exercise interventions that started at different times (06, 08, 10, 12, 14, 16, 18, and 20 AE) and were separated by at least 60 h from the previous one.

Figure 2

Effects of AE on blood pressure and arterial elasticity at different time points. Response of systolic blood pressure (SBP) (a) and its post-exercise changes (b) to chrono-exercise; Response of diastolic blood pressure (DBP) (c) and its post-exercise changes (d) to chrono-exercise; Response of apparent elastic modulus (EM) (e) and its post-exercise changes (f) to chrono-exercise. * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 3

Effects of AE on diameter at different time points. Response of the mean values of diameter (D_mean) (a) and its post-exercise changes (b) to chrono-exercise; Response of the maximum values of diameter (D_max) (c) and its post-exercise changes (d) to chrono-exercise; Response of the minimum values of diameter (D_min) (e) and its post-exercise changes (f) to chrono-exercise. * p < 0.05, ** p < 0.01.

Figure 4

Effects of AE on blood supply at different time points. Response of the mean values of center-line flow velocity (FV_mean) (a) and its post-exercise changes (b) to chrono-exercise; Response of the maximum values of center-line flow velocity (FV_max) (c) and its post-exercise changes (d) to chrono-exercise; Response of the minimum values of center-line flow velocity (FV_min) (e) and its post-exercise changes (f) to chrono-exercise; Response of the mean values of flow rate (FR_mean) (g) and its post-exercise changes (h) to chrono-exercise; Response of the maximum values of flow rate (FR_max) (i) and its post-exercise changes (j) to chrono-exercise; Response of the minimum values of flow rate (FR_min) (k) and its post-exercise changes (l) to chrono-exercise; The negative values of FR_min represent retrograde FR. * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 5

Effects of AE on wall shear stress at different time points. Response of the mean values of wall shear stress (WSS_mean) (a) and its post-exercise changes (b) to chrono-exercise; Response of the maximum values of wall shear stress (WSS_max) (c) and its post-exercise changes (d) to chrono-exercise; Response of the minimum values of wall shear stress (WSS_min) (e) and its post-exercise changes (f) to chrono-exercise; The negative values of WSS_min represent retrograde WSS; Response of oscillatory shear index (OSI) (g) and its post-exercise changes (h) to chrono-exercise. * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 6

Effects of AE on vascular resistance at different time points. Response of dynamic resistance (DR) (a) and its post-exercise changes (b) to chrono-exercise; Response of peripheral resistance (PR) (c) and its post-exercise changes (d) to chrono-exercise; Response of pulsatility index (PI) (e) and its post-exercise changes (f) to chrono-exercise. * p < 0.05, ** p < 0.01, *** p < 0.001.