Examining the effects of moderate intensity exercise and high intensity interval training on cerebral blood flow and neurovascular signalling factors during cycling

Introduction: Exercise is thought to induce beneficial effects on the cerebrovasculature through the stimulation of shear stress and cyclic strain, but the optimal exercise regimen to maximally activate these pathways is unknown. AIM: To compare moderate intensity cycling (65% VO2max for 30-minutes), clinical HIIT (4 x 4-minute bouts at 85%HRmax) and all-out HIIT (4 x 30-second sprints) on cerebral blood flow velocity (CBFv), partial pressure of end-tidal carbon dioxide (PETCO2) and representative markers of shear stress and cyclic strain: vascular endothelial growth factor (VEGF) and derivatives of nitric oxide (NO), nitrite (NO2) and nitrate (NO3). METHODS: Eight physically active (6 male, 2 female) participants completed the study. CBFv was measured as an index of cerebral blood flow using transcranial Doppler ultrasound, whilst total NO2/NO3 and VEGF concentrations were quantified from blood plasma. RESULTS: Moderate intensity cycling and clinical HIIT significantly increased CBFv (by ~19 cm/s and ~10 cm/s, respectively) and PETCO2 (~18 mmHg and ~9mmHg, respectively) compared to all-out HIIT (CBFv, p = 0.03, np2 = 0.7; PETCO2, p<0.01, np2 = 0.97). However, increases in CBFv did not translate to significant elevations in total NO2/NO3 for moderate intensity exercise (~19%), whilst clinical and all-out HIIT significantly elevated total NO2/NO3 (by 23% and 26%, respectively) (p<0.01, np2 = 0.9). No exercise protocol significantly up-regulated VEGF (p=0.08, np2 = 0.38). CONCLUSION: Clinical and all-out HIIT are likely to produce the best outcomes for the cerebrovasculature based upon their capacity to significantly elevate total NO2/NO3