Effectiveness of short-term heat acclimation for highly trained athletes

• DOI: 10.1007/s00421-011-2153-3
• Publication Date: 2011-09-13T14:34:59Z
• Authors: Andrew T. Garrett; Rob Creasy; Nancy J. Rehrer; Mark J. Patterson; James D. Cotter
• Keywords: Plasma volume; Male; Fever; Performance; Acclimatization; 612; Body Temperature; Young Adult; 03 medical and health sciences; 0302 clinical medicine; 616; Fluid regulation; Humans; Plasma Volume; Aldosterone; Exercise; Dehydration; Elite; 16. Peace & justice; Athletes; Exercise Test; Physical Endurance; Heat-Shock Response; Body Temperature Regulation

Effectiveness of short-term acclimation has generally been undertaken using untrained and moderately-trained participants. The purpose of this study was to determine the impact of short-term (5-day) heat acclimation on highly trained athletes. Eight males (mean ± SD age 21.8 ± 2.1 years, mass 75.2 ± 4.6 kg, VO(2peak) 4.9 ± 0.2 L min(-1) and power output 400 ± 27 W) were heat acclimated under controlled hyperthermia (rectal temperature 38.5 °C), for 90-min on five consecutive days (T(a) = 39.5 °C, 60% relative humidity). Acclimation was undertaken with dehydration (no fluid-intake) during daily bouts. Participants completed a rowing-specific, heat stress test (HST) 1 day before and after acclimation (T(a) = 35 °C, 60% relative humidity). HST consisted 10-min rowing at 30% peak power output (PPO), 10 min at 60% PPO and 5-min rest before a 2-km performance test, without feedback cues. Participants received 250 mL fluid (4% carbohydrate; osmolality 240-270 mmol kg(-1)) before the HST. Body mass loss during acclimation bouts was 1.6 ± 0.3 kg (2.1%) on day 1 and 2.3 ± 0.4 kg (3.0%) on day 5. In contrast, resting plasma volume increased by 4.5 ± 4.5% from day 1 to 5 (estimated from [Hb] & Hct). Plasma aldosterone increased at rest (52.6 pg mL(-1); p = 0.03) and end-exercise (162.4 pg mL(-1); p = 0.00) from day 1 to 5 acclimation. During the HST T(re) and f(c) were lowered 0.3 °C (p = 0.00) and 14 b min(-1) (p = 0.00) after 20-min exercise. The 2-km performance time (6.52.7 min) improved by 4 s (p = 0.00). Meaningful physiological and performance improvements occurred for highly trained athletes using a short-term (5-day) heat acclimation under hyperthermia control, with dehydration.