The optimal exercise intensity and modality for maximizing cerebral blood flow (CBF) and hence potential exposure to positive, hemodynamically derived cerebral adaptations is yet to be fully determined. This study compared CBF velocity responses between running and cycling across a range of exercise intensities. Twenty-six participants (12 females; age: 26 ± 8 years) completed four exercise sessions; two mode-specific maximal oxygen consumption (VO_2max ) tests, followed by (order randomized) two incremental exercise protocols (3-min stages at 35%, 50%, 65%, 80%, 95% VO_2max ). Continuous measures of middle cerebral artery velocity (MCAv), oxygen consumption, end-tidal CO₂ (P_ET CO₂ ), and heart rate were obtained. Modality-specific MCAv changes were observed for the whole group (interaction effect: p = .01). Exercise-induced increases in MCAv_mean during cycling followed an inverted-U pattern, peaking at 65% VO_2max (Δ12 ± 7 cm/s from rest), whereas MCAv_mean during running increased linearly up to 95% VO_2max (change from rest: Δ12 ± 13 vs. Δ7 ± 8 cm/s for running vs. cycling at 95% VO_2max ; p = .01). In contrast, both modalities had an inverted-U pattern for P_ET CO₂ changes, although peaked at different intensities (running: 50% VO_2max , Δ6 ± 2 mmHg; cycling: 65% VO_2max , Δ7 ± 2 mmHg; interaction effect: p = .01). Further subgroup analysis revealed that the running-specific linear MCAv_mean response was fitness dependent (Fitness*modality*intensity interaction effect: p = .04). Above 65% VO_2max , fitter participants (n = 16; male > 45 mL/min/kg and female > 40 mL/min/kg) increased MCAv_mean up to 95% VO_2max , whereas in unfit participants (n = 7, male < mL/min/kg and female < 35 mL/min/kg) MCAv_mean returned toward resting values. Findings demonstrate that modality- and fitness-specific profiles for MCAv_mean are seen at exercise intensities exceeding 65% VO_2max .

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