Date of Graduation

5-2016

Document Type

Thesis

Degree Name

Master of Science in Kinesiology (MS)

Degree Level

Graduate

Department

Health, Human Performance and Recreation

Advisor

Stavros A. Kavouras

Committee Member

Brendon MacDermott

Second Committee Member

Matthew Ganio

Abstract

Introduction: In dehydrated individuals thirst seems to disappear after ingestion of small amount of water before full rehydration. This phenomenon has been linked to oropharyngeal receptors. However, some researchers suggest that drinking to satisfy thirst is enough for optimal performance. It is well established that water deficit greater than 2% of body weight decreases exercise performance in the heat. No study has ever examined the effect hydration on exercise performance in the absence of thirst via oropharyngeal stimulation. Purpose: The purpose of this study is to examine the effect of dehydration on exercise performance and thermoregulation during exercise in the heat independently of thirst. Method: Five competitive male cyclists (age, 31.6±4.9 y, weight, 74.7±3.7 kg, height, 180.9±4.3 cm, VO2peak, 57.5±28 mL∙min-1∙kg-1) were performed 2 hours cycling in 35°C and 30% relative humidity after that they completed 5K time trial. Two experimental trials were performed: on Dehydration without Thirst (DEH): drinking 25 ml water every 5 min with no infusion in the nasogastric tube, and the other was euhydration not thirst (EUH): drinking 25 ml water every 5 min while infusing in the nasogastric tube enough fluid to match sweat losses. Results: Sweat rate during 5K time trial in the EUH trial (2.2±0.7 L/h) was higher than that in the DEH trial (1.9±0.1 L/h). In the EUH trial, % body weight loss (-0.1±0.3 %) was lower than that in the DEH trial (-2.2±0.2 %) during 2 hours cycling. The finishing time of the 5K in the EUH trial was faster than that in the DEH trial (12.9±0.5 and 13.4±0.5 min). Core temperature at the end of the 5K time trial in the EUH trial was lower than that in the DEH trial (39.0±0.1 and 39.5±0.8 ˚C). Mean skin temperature during the 5K time trial in the EUH trial was higher than that in the DEH trial. In both trials, there was no difference in the degree of thirst. Conclusion: In the EUH group, subjects completed faster the 5K time trial than in the DEH, probably due to lower thermoregulatory strain and better cardiovascular function.

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