Date of Graduation

8-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Kinesiology (PhD)

Degree Level

Graduate

Department

Health, Human Performance and Recreation

Advisor

Stavros A. Kavouras

Committee Member

Andy T. Mauromoustakos

Second Committee Member

Matthew S. Ganio

Third Committee Member

Brendon P. McDermott

Keywords

Exercise Performance, Hydration, Thermoregulation

Abstract

Purpose: The purpose of these studies was to observe the effect of dehydration on exercise performance while subjects were blinded to their hydration status. Methods: Study 1: Seven male cyclists (weight: 71±8 kg, body fat: 14±6%, VO2peak: 59.4±6 ml∙kg-1·min-1) exercised for 2 hours on a cycle ergometer at 55% VO2peak, in a hot-dry environment (35°C, 30% rh), with a nasogastric (NG) tube under euhydrated (EUH-NT) and hypohydrated (DEH-NT) conditions. In both trials, thirst was matched by drinking 25 mL every 5 min. In the EUH-NT trial sweat losses were fully replaced via the NG tube. Following the 2 hours of steady state, the cyclists completed a 5-kilometer cycling time trial at 4% grade. Study 2: Eleven male cyclists (weight 75.8±6.4 kg, VO2peak: 64.9±5.6 mL·kg·min-1, body fat: 12.0±5.8%) performed three sets of criterium-like cycling, consisting of 20 min of steady state cycling at 50% peak power output, each followed by a 5-km time-trial at 3% grade. Subjects completed the protocol on two separate occasions either hypohydrated (HYP) or euhydrated (EUH). In both trials, subjects ingested 25 mL every 5 min during the steady-state and 25 mL every 1-km during the 5-km time-trials. In the EUH trial, sweat losses were fully replaced via intravenous infusion of isotonic saline while in the DEH trial, a sham IV was instrumented. Results: In Study 1, cyclists completed the 5-km time trial faster in the EUH-NT trial compared to the DEH-NT trial (23.2±0.2 vs. 22.3±0.3 km·h-1, P<0.05), while producing higher power output (295±29 vs. 270±26 W, P<0.05). In Study 2, during the second and third time-trials, subjects displayed faster speed in the EUH trial (27.5±3.0 and 27.2±3.1 km·h-1) compared to the HYP trial (26.2±2.9 and 25.5±3.3 km·h-1; both P<0.05). Core temperature (Tre) was also higher in the HYP trial throughout the third steady-state (P<0.05) and continued to be higher throughout the third 5-km time-trial (P<0.05). Conclusions: These data suggest that full fluid replacement, even in a blinded manner, provided a performance advantage by maintaining better hydration state. This benefit seems to be associated with the lower thermoregulatory strain, due to lower core temperatures.

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