Dehydration & Performance – Part 2

Following up Part 1 of this series, I wanted to give you information on exactly WHAT makes you dehydrated. Let’s take a closer look at what electrolytes you are losing through your sweat and how to replenish them!

Many people think the best way to rehydrate is through water and/or sports drinks. While these are definitely helpful, there are actually many FOODS that can give you optimal hydration.

I planned on posting my Part 2 here on the blog, but it was accepted to the STACK magazine (yay!) so please follow the link below to read on…

Dehydration & Performance – Part 2 on STACK

If you’re interested in making your very own sports drink, try the tart cherry sports drink!

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Dehydration & Performance – Part 1

In January, a new review paper was published on dehydration. It specifically looks at the physiology, assessment and performance effects of many different dehydration research experiments. One reason why I like to read review papers is that they include TONS of research articles while giving you a summary of what every researcher has found up to this point. Nerdy? Yes, I know.

Instead of you reading a thirty page paper, this post is all about what they found and how it can help you as an athlete!


How do you know if you’re hydrated?

This review tells us the best way to get a baseline for comparing hydration is via consecutive daily measures of first morning, postvoid and nude body mass, with providing fluid the night before (1-2L). Without knowing your hydrated body mass, it will be hard to tell if you’re dehydrated before you actually start your workout, race, etc.

Your urine should be a clear color like light lemonade, not like apple juice

What happens when the body is dehydrated and then exercises?

Dehydration reduces the sweating rate for any given body core temperature, decreases heat loss and increases heat storage. Because of this, your heart rate increases and perceived exertion increases during work {aka performance or exercise}.

What is more affected by dehydration – endurance or strength workouts?

Many different research articles show the consequences of dehydration to endurance performance include a shorter time to exhaustion, a reduction in intensity or BOTH. It’s widely known that dehydration as little as 2% body mass can affect performance negatively, and that is mainly due to endurance studies. Dehydration by 2% to 4% body mass produces an added challenge for the body to meet blood flow needs – making the heart work harder – giving you a higher heart rate at a task (running, lifting, swimming, etc) that you have been training for – causing you to quit sooner (reduce intensity or actually quit) – causing you to wonder why you couldn’t perform as well.

Dehydration by 2% to 4% body mass also reduces VO2max. If you’re unfamiliar with VO2max, this is a measurement done in many athletic assessments to determine how well your body is using oxygen and ultimately measures power. This makes sense that dehydration is reducing power overall because they body just cannot work as hard. The table below shows different studies done, the amount of dehydration the athletes experienced and how it affected their VO2max or power or ability to use oxygen by the muscles.


“A reduction in VO2max when dehydrated makes incremental or constant-rate exercise more difficult to sustain or require a slowing of self-paced exercise to achieve a similar sensation of effort” – Source

The findings from this review show that effects of dehydration on strength sports are small. Any definitive mechanism by which dehydration may impair strength is still unknown. One function researchers want to look at more closely is the possibility that dehydration may affect strength through an athlete’s mental ability. Brain volume may actually shrink in response to severe and acute dehydration. For many researchers, it seems unlikely but it hasn’t been looked at enough to determine.

Why would dehydration impair cognition? It’s widely known that dehydration has a negative effect on mood and can cause unpleasant symptoms like dry mouth, thirst and headache. Some studies that have been done report alterations in mood such as tiredness, decreased alertness and others related to mood. The ability to overcome these stressors and maintain an effective level of performance is called cognitive resiliency.

Imagine the sports where cognitive function is extremely important – golfers, baseball pitcher, gymnastics, pole vaulting. Cognitive function is obviously important for everyone, but these sports rely heavily on their mental ability to stay focused.

One endurance example noted is a 12-km race where there are 2 groups of runners: hydrated and 2% dehydrated. The two groups finished at 2% or 4% dehydrated, with the latter group being the ones that started dehydrated. Performance time was 5% slower when completing the race with 4% dehydration and these runners reported a significantly greater perception of effort, thirst, tension, anxiety and fatigue.

Another study measured the impact of dehydration on manual labor workers during an actual work day. Performance was compared between those who consumed fluid and those who did not. They found when workers were dehydrated, productivity during an entire work day of stacking and debarking pulpwood was reduced by 12%.

A progressive decline in timed skills and shooting skills was reported as the level of dehydration increased (1-4%) in male basketball players. Players reported feeling lightheaded and more body fatigue at 3-4% dehydration.

From the many examples noted in this review {there are many more!}, it seems that the impact of dehydration is dependent upon the actual sport, skill or task being studied. Tasks with higher aerobic/endurance such as running or day-long manual labor are significantly impaired by dehydration while strength/power are highly variable.

How do you stay hydrated?

1. Get your “hydrated” body weight. This is the easiest way to measure and know. There are other tools for measuring hydration such as a refractometer which measures specific gravity of the urine (aka you pee in a cup and a strip tests it)… but this takes tools and more time. You can compare your weight while traveling or anywhere you might be.

2. Aim for 0.5-1 ounce per pound of body weight per day in fluids. If you don’t drink much, start with 0.5 ounce per pound.

3. Buy or use a water bottle where you can measure what you’re drinking. See how you feel when you drink what is actually recommended.

4. Avoid drinking too much caffeine, soda or other non-water based beverages. The bottom line is that the body NEEDS water. If you crave soda, try sparkling water. If you hate that, try adding a splash of 100% juice. Drink unsweetened tea. If you drink lots of coffee, start switching between one cup coffee – one glass water. Start where you can and work your way to drinking more water!

5. You will pee. A lot. Get used to it.

SCAN (Sports, Cardiovascular, and Wellness Nutrition) is a group I belong to within the Academy of Nutrition & Dietetics… they have some great fact sheets for posting for yourself, other athletes, etc. Here are links to the hydration fact sheets:

Performance Hydration
Exercise Hydration
Understanding Sweat Loss

This is Part 1 of the hydration series! Please let me know if you have any specific questions you want answered as we go along with this series. Next we will cover electrolytes {what do you really lose in sweat?}, eating foods that help with hydration, and how to hydrate {timing schedule} prior to an event or training session. If you want to read the full review paper, just email me for a copy.

*Photo from freedigitalphotos.net

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