Journal of Sports Science and Medicine
Journal of Sports Science and Medicine
ISSN: 1303 - 2968   
Ios-APP Journal of Sports Science and Medicine
Androit-APP Journal of Sports Science and Medicine
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©Journal of Sports Science and Medicine (2013) 12, 197 - 204

Research article
Effect of the Volume of Fluid Ingested on Urine Concentrating Ability During Prolonged Heavy Exercise in a Hot Environment
Hidenori Otani1, , Mitsuharu Kaya2, Junzo Tsujita3
Author Information
1 Faculty of Health Care Sciences, Himeji Dokkyo University, Himeji, Japan
2 General Education Center, Hyogo University of Health, Kobe, Japan
3 Department of Health and Sport Sciences, Hyogo College of Medicine, Nishinomiya, Japan

Hidenori Otani
✉ Faculty of Health Care Sciences, Himeji Dokkyo University, 7-2-1 Kamiono, Himeji, Hyogo 6708524, Japan
Email: hotani@himeji-du.ac.jp
Publish Date
Received: 04-12-2012
Accepted: 19-02-2013
Published (online): 01-03-2013
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ABSTRACT

This study examined the effect of the volume of fluid ingested on urine concentrating ability during prolonged heavy exercise in a hot environment at low levels of dehydration. Seven healthy males performed 105 min of intermittent cycle exercise at 70% maximum oxygen uptake (32°C, 60% relative humidity) while receiving no fluid ingestion (NF), voluntary fluid ingestion (VF), partial fluid ingestion equivalent to one-half of body mass loss (PF), and full fluid ingestion equivalent to body mass loss (FF). Fluid (5°C, 3.4% carbohydrate, 10.5 mmol·L-1 sodium) was ingested just before commencing exercise and at 15, 33, 51, 69, and 87 min of exercise, and the total amount of fluid ingested in PF and FF was divided into six equal volumes. During exercise, body mass loss was 2.2 ± 0.2, 1.1 ± 0.5, 1.1 ± 0.2, and 0.1 ± 0.2% in NF, VF, PF, and FF, respectively, whereas total sweat loss was about 2% of body mass in each trial. Subjects in VF ingested 719 ± 240 ml of fluid during exercise; the volume of fluid ingested was 1.1 ± 0.4% of body mass. Creatinine clearance was significantly higher and free water clearance was significantly lower in FF than in NF during exercise. Urine flow rate during exercise decreased significantly in NF. There were significant decreases in creatinine and osmolar clearance and was a significant increase in free water clearance during exercise in NF and VF. Creatinine clearance decreased significantly and free water clearance increased significantly during exercise in PF. There was no statistical change in urinary indices of renal function during exercise in FF. The findings suggest that full fluid ingestion equivalent to body mass loss has attenuated the decline in urine concentrating ability during prolonged heavy exercise in a hot environment at low levels of dehydration.

Key words: Body fluid, dehydration, heat stress, rehydration, renal function


           Key Points
  • During prolonged heavy exercise in a hot environment at low levels of dehydration, fluid ingestion equivalent to body mass loss results in no changes in urinary indices of renal function.
  • Fluid ingestion equivalent to body mass loss can attenuate the decline in urine concentrating ability during exercise.
  • Ad libitum or voluntary fluid ingestion is ineffective in reducing the decline in urine concentrating ability during exercise.
 
 
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