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/Mentor

Kavouras, Stavros A.

Committee Member

Mauromoustakos, Andronikos T.

Second Committee Member

Ganio, Matthew S.

Third Committee Member

McDermott, Brendon P.

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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