Mild hypohydration impairs cycle ergometry performance in the heat: A blinded study. (12th February 2019)

• Record Type: Journal Article
• Authors: Adams, J.D.; Scott, Dylan M.; Brand, Natasha A.; Suh, Hyun‐Gyu; Seal, Adam D.; McDermott, Brendon P.; Ganio, Matthew S.; Kavouras, Stavros A.
• Is Part Of: Scandinavian journal of medicine & science in sports. Volume 29:Number 5(2019)
• Page Start: 686
• Page End: 695
• Publication Date: 2019-02-12
• Subjects: cycling -- heat stress -- time trial -- water intake; Sports medicine -- Periodicals; Sports -- Physiological aspects -- Periodicals; Sports -- Periodicals; 617.1027
• DOI: 10.1111/sms.13386
• Languages: English
• ISSNs: 0905-7188

Abstract

Abstract : The aim of the present study was to observe the effect of mild hypohydration on exercise performance with subjects blinded to their hydration status. Eleven male cyclists (weight 75.8 ± 6.4 kg, VO2peak : 64.9 ± 5.6 mL/kg/min, body fat: 12.0 ± 5.8%, Powermax : 409 ± 40 W) performed three sets of criterium‐like cycling, consisting of 20‐minute steady‐state cycling (50% peak power output), each followed by a 5‐km time trial at 3% grade. Following a familiarization trial, subjects completed the experimental trials, in counter‐balanced fashion, on two separate occasions in dry heat (30°C, 30% rh) either hypohydrated (HYP) or euhydrated (EUH). In both trials, subjects ingested 25 mL of water every 5 minutes during the steady‐state and every 1 km of the 5‐km time trials. In the EUH trial, sweat losses were fully replaced via intravenous infusion of isotonic saline, while in the HYP trial, a sham IV was instrumented. Following the exercise protocol, the subjects' bodyweight was changed by −0.1 ± 0.1% and −1.8 ± 0.2% for the EUH and HYP trial, respectively ( P < 0.05). During the second and third time trials, subjects averaged higher power output (309 ± 5 and 306 ± 5 W) and faster cycling speed (27.5 ± 3.0 and 27.2 ± 3.1 km/h) in the EUH trial compared to the HYP trial (Power: 287 ± 4 and 276 ± 5 W, Speed: 26.2 ± 2.9 and 25.5 ± 3.3 km/h, all P < 0.05). Core temperature ( T re ) was higher in the HYP trial throughout the third steady‐state and 5‐km time trial ( P < 0.05). These data suggest that mild hypohydration, even when subjects were unaware of their hydration state, impaired cycle ergometry performance in the heat probably due to greater thermoregulatory strain.