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.