The influence of a mild thermal challenge and severe hypoxia on exercise performance and serum BDNF

Aim: To examine the isolated and combined effects of severe hypoxia and a mild thermal challenge on performance, physiological measures, cognition, and serum brain-derived neurotrophic factor (BDNF). Methods: Nine trained male athletes (age: 23 ± 3 years; W_max: 333 ± 45 W) completed four experimental trials (CON: 15 °C/0 m, ALT: 15 °C/3800 m, TEMP: 25 °C/0 m, ALT + TEMP: 25 °C/3800 m) in a double blind, randomized, cross-over design. Subjects cycled for 30 min in a self-paced test starting at 75 % W_max, their goal was to ‘perform as much work as possible in 30 min.’ Power output, heart rate, blood lactate, pulse oximetry, core and skin temperature, thermal sensation, ratings of perceived exertion, reaction time (RT), and BDNF were assessed. Results: The amount of work produced in 30 min was reduced by temperature (F(1,8) = 7.1; p = 0.029; 360 ± 19 kJ in 15 °C; 344 ± 18 kJ in 25 °C) and altitude (F(1,8) = 94.2; p < 0.001; 427 ± 24 kJ at sea level; 277 ± 15 kJ at altitude), yet there was no interaction effect. Altitude increased mean RT (F(1,8) = 8.0; p = 0.022; 281.9 ± 9.4 ms at sea level; 289.3 ± 10.0 ms at altitude) and RT variability (F(1,8) = 8.5; p = 0.020; 44 ± 3 ms at sea level: 50 ± 4 ms at altitude). Exercise increased BDNF (F(1,8) = 15.2; p = 0.005; PRE: 21.8 ± 1.3 ng/mL; POST: 26.5 ± 2.1 ng/mL). Conclusion: Exercise capacity was significantly reduced due to an increase in altitude (3800 m; −34.3 %) or a 10 °C increase in ambient temperature (−3.2 %). The combination of both stressors showed to be additive (−38.0 %). Altitude induced an increase in RT and RT variability presenting a deterioration in cognitive functioning during acute hypoxia. Exercise significantly increased BDNF, but no effect of altitude on the BDNF concentration was observed.