title: Time course of natural heat acclimatization in well-trained cyclists during a 2-week training camp in the heat.
abstract: 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.
authors.affiliation: Athlete Health and Performance Research Centre, Aspetar Orthopaedic Sports Medicine Hospital, Doha, Qatar; Department of Nutrition, Exercise and Sport Sciences, Section of Human Physiology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Karlsen
authors.forename: L
authors.initials: L
authors.lastname: Nybo
authors.forename: S J
authors.initials: SJ
authors.lastname: Nørgaard
authors.forename: M V
authors.initials: MV
authors.lastname: Jensen
authors.forename: T
authors.initials: T
authors.lastname: Bonne
authors.forename: S
authors.initials: S
authors.lastname: Racinais
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D054874:Athletic Performance / Q000502:physiology*; D001642:Bicycling / Q000502:physiology*; D001833:Body Temperature Regulation / Q000502:physiology; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D006813:Humidity; D008297:Male; D013997:Time Factors
keywords: Individual response; cycling time trial; heat response test; plasma volume expansion; self-paced exercise; sweat rate; sweat sodium concentration