Karlsen, Anders2; Nybo, Lars5; Nørgaard, S J3; Jensen, M V3; Bonne, Thomas Christian6; Racinais, S2
1 Integrated Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, Københavns Universitet2 Athlete Health and Performance Research Centre, Aspetar, Qatar Orthopaedic and Sports Medicine Hospital, Doha3 Institut for Idræt og Ernæring, Københavns Universitet4 Department of Exercise and Sport Sciences, Faculty of Science, Københavns Universitet5 Integrated Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, Københavns Universitet6 Department of Exercise and Sport Sciences, Faculty of Science, Københavns Universitet
The aim of this study was to determine the time course of physiological adaptations and their relationship with performance improvements during 2 weeks of heat acclimatization. Nine trained cyclists completed 2 weeks of training in naturally hot environment (34 ± 3 °C; 18 ± 5% relative humidity). On days 1, 6, and 13, they performed standardized heat response tests (HRT-1, 2, 3), and 43.4-km time trials in the heat (TTH-1, 2, 3) were completed on days 2, 7, and 14. Within the first 5-6 days, sweat sodium concentration decreased from 75 ± 22 mmol/L to 52 ± 24 mmol/L, sweat rate increased (+20 ± 15%), and resting hematocrit decreased (-5.6 ± 5.4%), with no further changes during the remaining period. In contrast, power output during TTHs gradually improved from TTH-1 to TTH-2 (+11 ± 8%), and from TTH-2 to TTH-3 (+5 ± 4%). Individual improvements in performance from TTH-1 to TTH-2 correlated with individual changes in hematocrit (assessed after the corresponding HRT; r = -0.79, P < 0.05), however, were not related to changes in performance from TTH-2 to TTH-3. In trained athletes, sudomotor and hematological adaptations occurred within 5-6 days of training, whereas the additional improvement in performance after the entire acclimatization period did not relate to changes in these parameters.
Scandinavian Journal of Medicine and Science in Sports, 2015, Vol 25, Issue Suppl. 1, p. 240-249