Blood-brain barrier integrity may be threatened by exercise in a warm environment

Abstract
Seven active men were recruited to examine changes in the serum concentration of S100β, a proposed peripheral marker of blood-brain barrier permeability, following prolonged exercise in temperate (T) and warm (W) conditions. Subjects were seated immersed to the neck in water at 35.0 (0.1)°C (T) or 39.0 (0.1)°C (W) for 30 min. Subjects then entered a room maintained at either 18.3 (1.8)°C (T) or 35.0 (0.3)°C (W) and completed 60 min of cycle exercise at 60% peak oxygen uptake. Serum S100β concentration was elevated after exercise in the W trial (+0.12 (0.10) μg/l; P = 0.02) but not after the T trial ( P = 0.238). Water immersion and exercise elevated core temperature by 2.1 (0.5)°C to 39.5 (0.3)°C at the end of exercise in the W trial compared with a 0.9 (0.2)°C increase during the T trial ( P < 0.001). Weighted mean skin temperature was higher throughout the W trial compared with the T trial ( P < 0.001). Heart rate ( P < 0.001) and blood glucose ( P < 0.001) and lactate ( P < 0.001) concentrations were elevated to a greater extent during exercise in the W trial than in the T trial. Ratings of perceived exertion ( P < 0.001) and thermal comfort ( P < 0.001) were markedly higher throughout the W trial than in the T trial. The results of this study demonstrate that serum S100β was elevated after water immersion and prolonged exercise in a warm environment, suggesting that blood-brain barrier permeability may be altered.