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Passive dehydration reduces muscle thickness after resistance exercise.
Casey R Appell1, Nigel C Jiwan1,2, Yasuki Sekiguchi1
1Department of Kinesiology and Sport Management, Texas Tech University, Lubbock, TX, USA.
Journal of Sports Sciences
|January 27, 2025
Summary
Dehydration significantly impacts fluid balance during resistance exercise in trained men. While dehydration reduces total body fluid and muscle thickness, it may help maintain plasma volume post-exercise.
Area of Science:
- Exercise Physiology
- Sports Science
- Human Physiology
Background:
- Dehydration significantly impacts plasma osmolality, affecting whole-body fluid balance.
- Fluid shifts within muscles during resistance exercise (RE) can be influenced by hydration status.
Purpose of the Study:
- To investigate the effects of dehydration on the changes in whole-body fluid balance induced by resistance exercise in resistance-trained (RT) men.
Main Methods:
- Fourteen RT men underwent two identical RE sessions: one in a euhydrated (EUHY) state and one in a dehydrated (DEHY) state induced by 24-hour fluid restriction.
- Measurements included total body fluid, urine osmolality (Uosmo), urine specific gravity (USG), plasma osmolality (Posmo), hematocrit (HCT), and muscle thickness, with plasma volume change (%ΔPV) calculated from HCT.
Main Results:
- Dehydrated conditions resulted in significantly lower total body fluid (2.6% less) and muscle thickness (13.0% less) compared to euhydrated conditions.
- Plasma osmolality, urine osmolality, and urine specific gravity were significantly higher in the dehydrated state throughout the study.
- Plasma volume decreased by 12.5% five minutes after resistance exercise compared to pre-exercise levels, regardless of hydration status.
Conclusions:
- Dehydration during resistance exercise alters whole-body fluid balance in trained men.
- Greater fluid retention and intramuscular fluid efflux observed during dehydration may contribute to maintaining plasma volume after exercise.
- These findings highlight the complex interplay between hydration status, fluid shifts, and exercise performance.
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