Most people regulate their hydration status exceptionally well on a day-to-day basis. However, when exercise is thrown into the equation, hydration status can be drastically altered and many athletes ignore simple physiological signs that could indicate dehydration. Mild dehydration of 2-3% can negatively affect both physical and cognitive performance, ultimately leading to a decrease in sports performance. In addition, many athletes begin training and competition in a dehydrated state, which can decrease training quality and intensity, increase the amount of stress on the body, and impair the immune system.
Hydration status can be measured quickly, easily and relatively accurately using a combination of the following methods. If two (or all three) methods indicate dehydration, you are most likely dehydrated and should undertake a rehydration strategy.
1. Urine Colour and Frequency
Assessing your urine colour provides a quick snapshot of your hydration status. Urine of a dark yellow (apple juice) colour indicates dehydration, whereas clearer (lemonade colour) urine indicates you are adequately hydrated. However, caution needs to be taken if you have drunk within the hour prior to urination, as the colour may not represent your hydration status. Urine frequency also provides a good measure of hydration status, if you are urinating regularly throughout the day you are likely to be hydrated, whereas if your urine frequency is low and you haven’t urinated in several hours, you are likely to be dehydrated.
2. Thirst Perception
Thirst occurs after dehydration is present, and therefore if you are thirsty, you are already dehydrated and should consume fluid. As your perception of thirst increases (you become more thirsty), the severity of dehydration increases. However, you need to be cautious, as the absence of thirst does not mean you are not dehydrated. Additionally, thirst can be alleviated without you returning to euhydration (normal hydration status).
3. Body Mass
- Monitoring Daily Fluid Balance: You should maintain a stable day-to-day body mass when weighed first thing in the morning (prior to breakfast). If your body mass is over 1.5% below previous measures this may indicate dehydration. Over the long term, changes in muscle and fat mass need to be considered for this measure to be accurate.
- Monitoring Acute Changes In Hydration Status: Rapid changes in hydration status can be calculated by quantifying the difference between pre-exercise and post-exercise body mass. Consume 150% of this difference over the 2-3 hours post exercise to return to euhydration. (Use the following equation to work out your fluid needs post exercise. The pre and post exercise body mass values are in kilograms).
(Pre Exercise Body Mass – Post Exercise Body Mass) x 1.5 = ……….. L
About the Author
Mark Funnell holds a BSc (Honours) degree in Sport and Exercise Science and an MSc in Sport and Exercise Nutrition from Loughborough University. He is currently working as a Performance Nutritionist for the England and Wales Cricket Board with both the England Women’s Academy and Midlands Regional Disability Cricket squads. Additionally, Mark is a graduate member of the Sport and Exercise Nutrition Register (SENr), an ISAK Level 1 Anthropometrist and a UK Anti-Doping advisor.