The independent and combined effects of aerobic exercise intensity and dose differentially increase post-exercise cerebral shear stress and blood flow.

ABSTRACT

This research examined the impact of aerobic exercise intensity and dose on acute post-exercise cerebral shear stress and blood flow. Fourteen young adults (27 ± 5 years of age, eight females) completed a maximal oxygen uptake ( V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_2}\max }}$ ) treadmill test followed by three randomized study visits treadmill exercise at 30% of V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_2}\max }}$ for 30 min, 70% of V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_2}\max }}$ for 30 min and 70% of V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_2}\max }}$ for a duration that resulted in caloric expenditure equal to that in the 30% V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_2}\max }}$ visit (EqEE). A venous blood draw and internal carotid artery (ICA) ultrasound were collected before and immediately following exercise. ICA diameter and blood velocity were determined using automated edge detection software, and blood flow was calculated. Using measures of blood viscosity, shear stress was calculated. Aerobic exercise increased ICA shear stress (time P = 0.005, condition P = 0.012) and the increase was greater following exercise at 70% V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_2}\max }}$ (∆4.1 ± 3.5 dyn/cm2) compared with 30% V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_2}\max }}$ (∆1.1 ± 1.9 dyn/cm2; P = 0.041). ICA blood flow remained elevated following exercise (time P = 0.002, condition P = 0.010) with greater increases after 70% V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_2}\max }}$ (Δ268 ± 150 mL/min) compared with 30% V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_2}\max }}$ (∆125 ± 149 mL/min; P = 0.041) or 70% V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_2}\max }}$ EqEE (∆127 ± 177 mL/min; P = 0.004). Therefore, aerobic exercise resulted in both intensity- and dose-dependent effects on acute post-exercise ICA blood flow whereby vigorous intensity exercise provoked a larger increase in ICA blood flow compared to light intensity exercise when performed at a higher dose.