title: Mild hypohydration decreases cycling performance in the heat.
abstract: BACKGROUND
  Hypohydration exceeding 2% of body mass decreases exercise performance. However, the effects of mild hypohydration (<2%) are not clear.
  
  
  OBJECTIVE
  The aim of this study was to determine the effects of mild hypohydration on cycling performance during a simulated-hill circuit course in a warm environment (32.5°C ± 0.5°C).
  
  
  METHODS
  Ten trained male cyclists (age, 30 ± 7 yr; mass, 78.4 ± 9.5 kg; height, 1.80 ± 0.01 m; V˙O2max, 52.4 ± 3.3 mL·min·kg; and Powermax, 355 ± 29 W) performed a cycling circuit three times on a laboratory ergometer consisting of 5 km at 50% of maximum power output and 5 km at an all-out pace, followed by a 5-min rest every 5 km. Subjects started the performance test either euhydrated (EUH) or hypohydrated (HYP), by 0% ± 0% and -1.0% ± 0.1% of body mass, respectively.
  
  
  RESULTS
  Mean speed at the first, second, and third 5-km simulated-hill cycling was higher in the EUH (28.1 ± 3.1, 27.7 ± 3, and 27.0 ± 3.6 km·h) than that in the HYP trial (27.0 ± 2.9, 26.1 ± 3.7, and 25.9 ± 3.6 km·h) (P < 0.05). Mean power output at the first, second, and third 5-km simulated-hill cycling was greater in the EUH (284 ± 55, 266 ± 53, and 254 ± 58 W) than that in the HYP trial (272 ± 56, 250 ± 61, and 240 ± 57 W) (P < 0.05). Gastrointestinal temperature at the end of the first, second, and third 5-km simulated-hill cycling was greater in the HYP (38.3°C ± 0.4°C, 38.4°C ± 0.2°C, and 38.6°C ± 0.2°C) than that in the EUH trial (38.1°C ± 0.3°C, 38.1°C ± 0.3, and 38.3°C ± 0.3°C) (P < 0.05). Overall, sweat sensitivity during the circuit course was greater in the EUH (115 ± 58 g·°C·min) versus HYP trial (67 ± 19 g·°C·min) (P < 0.05). Furthermore, RPE and heart rate were similar and near maximal between trials (P > 0.05).
  
  
  CONCLUSIONS
  The data showed that mild hypohydration decreased cycling performance, possible by inducing greater thermal and cardiovascular strain.
authors.affiliation: Department of Nutrition and Dietetics, Harokopio University, Athens, Greece.
authors.forename: Costas N
authors.initials: CN
authors.lastname: Bardis
authors.forename: Stavros A
authors.initials: SA
authors.lastname: Kavouras
authors.forename: Lena
authors.initials: L
authors.lastname: Kosti
authors.forename: Marietta
authors.initials: M
authors.lastname: Markousi
authors.forename: Labros S
authors.initials: LS
authors.lastname: Sidossis
mesh_terms: D000328:Adult; D054874:Athletic Performance / Q000502:physiology*; D001642:Bicycling / Q000502:physiology*; D001831:Body Temperature; D003681:Dehydration / Q000503:physiopathology*; D005080:Exercise Test; D006339:Heart Rate; D006358:Hot Temperature; D006801:Humans; D008297:Male; D005082:Physical Exertion / Q000502:physiology*; D013546:Sweating; D013894:Thirst; D055815:Young Adult