Cognitive function and blood-brain barrier permeability during exercise in the heat: Effect of fitness and bovine colostrum supplementation

•Cognitive executive function was not impaired during intense exercise in the heat.•Neither fitness or blinded bovine colostrum supplementation affected performance.•Moderately fit subjects had less cerebral deoxygenation than fit counterparts.•Blood-brain barrier integrity maintained, despite combined exercise+heat strain.

We investigated whether fitness and bovine colostrum supplementation modulates cognition and cerebrovascular function during exercise in the heat in this placebo-controlled, double-blind study. Seven highly-fit (HF, V̇O2peak 64±4 mL kg−1 min−1) and eight moderately-fit (MF, 46±4 mL kg−1 min−1) men completed two randomised, 90-min exercise bouts (30 °C, 50% RH) after 7-d of bovine colostrum supplementation (COL: 1.7 g kg−1 d−1) or placebo (CON: cornflour). Multi-mode exercise consisted of: 15-min fixed-load cycling at 50% heart rate reserve (HRR; Cycle1), 30-min fixed-speed running (80% HRR; Run1), 30-min time trial (Run2), then repeating cycling (Cycle2). Heart rate, end-tidal PCO2, cerebral oxygenation, a marker of blood-brain barrier integrity ([S100ß]), cognition (Stroop test) and perceptions were recorded at rest, Cycles1 and 2, and 5 h post-exercise. MF had less cerebral deoxygenation during exercise (MF: −5±14, HF: 8±7 μM L−1), but [S100ß] was unchanged across fitness and colostrum supplementation. Hypocapnia was evident from Cycle1 to Run2 with end-tidal PCO2 decreasing from 36±5 to 31±5 mmHg in both trials. Response time to simple and complex tasks decreased during exercise by ~83 and ~301 ms, compared to rest in both fitness groups in both trials. The time difference between complex and simple tasks (i.e. decision-making time) also decreased from 724±200 (Rest) to 552±326 (Cycle1), 565±148 (Cycle2) and 515±216 ms (post-exercise; pooled results). We conclude that fitness per se does not modulate cognitive executive function or blood-brain barrier permeability during comparable, relative-intensity exercise in the heat, and that colostrum supplementation had negligible effect on performance, cognitive or cerebrovascular functioning.