Everything You Need To Know About Hydration
We all know hydration is important! It’s been ingrained into us for most of our lives and if you’re in the sporting world then it’s probably a little bit more important to you too.
This blog is going to ultimately expand on why it’s important, where we obtain our fluid from, where we lose it and what happens when those losses outweigh the gains!
Then we’ll dive into how to combat these, tackling issues with popular recommendations for hydration, educating you on how to measure your own hydration status at home and how to create your very own hydration plan with not just how much to drink but what to take in, when to do it and why! This is designed to be your one stop shop for all things hydration so pour yourself a glass of water and let’s dive in.
Hydration, Dehydration and Performance
Before we dive into dehydration and the impact it has on the body, we first need to contextualise where fluid comes from and how it is lost. To do this we’re going to use the concept of daily water balance. Daily water balance is quite simply the balance of fluid gain vs fluid loss in the body across one day. Below is an image representing this with estimated amounts of fluid loss and gain for an average SEDENTARY male.
As you can see, most fluid is lost from urine then from the skin via sweat, followed by water produced by respiration and finally the fluid that is present in faeces! On the flip side, we obtain most of our water through drinks (no surprises there), then through food and finally some is produced via metabolic processes in the body.
Now, it’s important to note that these values are estimations for a sedentary male and both loss and gain of fluid are highly variable and totally dependent on you, your activity level, the climate you live in and many other things. For example, athletes, like most of you reading this, will lose significantly more sweat via both sweat and respiration than this example above.
They will likely drink more fluids to combat this too. But it should highlight the importance of an individualised hydration plan tailored to you! Ok sweet, water balance ticked off. Let’s now look at what happens when fluid gain outweighs fluid loss.
I am of course meaning dehydration and we’re going to look at it in the context of exercise performance. The fact of the matter is that dehydration decreases performance. It’s been shown to reduce power output, time to fatigue and aerobic capacity.
This decrease in performance is seen at 2% losses of body mass and has even been shown to reduce performance by 30%.
It’s also highly likely that a drop in performance would be seen at losses of less than 2%. These drops in performance are down to a number of things! Here are just a few of the potential reasons dehydration impairs performance:
Reduction in blood volume and thus impaired oxygen transport
Decreased sweat rate and decreased heat dissipation that lead to an increase of core temperature
Increased rate of muscle glycogen use so you fatigue quicker.
This is why it’s so important to have a hydration plan in place, and what’s more a personalised hydration plan as blanket recommendations often don’t take into account the variation in different sports, climate and athletes! All of which can have a profound effect on your fluid loss.
Why it is important to monitor hydration
Before we dive into how to put together a tailored nutrition plan, we first want to look at why we actually need one. You’d think, with our bodies being so good at homeostasis, they’d just send signals in the form of thirst to get us to drink right?!
And for the most part you’re spot on! Our kidneys regulate our fluid intake, they are triggered to either retain or excrete water depending on the blood plasma Osmolality (the concentration of solutes in the blood). On top of this the brain of course has something to say!
When there is insufficient water in the body, the blood volume and osmolality is reduced but as well as stimulating the kidneys retain water, decreases in blood pressure and osmoreceptors in the hypothalamus also stimulate the thirst centre, increasing thirst and leading to us drinking more.
Simple right?!
Well as with hunger, there are a number of things that can interfere with this thirst sensation and when we are training and losing water at a faster rate than usual, this process may not be able to keep up with the water loss which is why thirst sometimes isn’t enough and we need to have a hydration plan in place!
A Framework For Hydration Success
Here we’re going to outline a framework for hydration success and pick apart general recommendations to leave you with a hydration plan that means dehydration is a rare occurrence!
The framework that we’re going to be following is a 3 step plan as follows!
Ensure you go into training adequately hydrated
Prevent dehydration whilst training
Replenish what is lost (not just in fluid)
A huge part of the first step will ultimately be measuring your own hydration status. How can you know you're hydrated if you don’t know what it looks like?! Well lucky for us there are several ways that you can measure your hydration status and there are advantages and disadvantages to all of them. Some measures look at total body water by using either an isotope dilution method which is thought to be the gold standard of hydration status or bio impedance. Now bioimpedance is cheap and non invasive but there are several confounding factors that can interfere with the results. You can also measure hydration status using blood plasma markers but these require blood samples and are intrusive
Seen most of us probably don’t have the access or the need to use things like this. This is where the wonderfully available resource of urine comes in handy. The colour of your urine is a relatively good indicator of how hydrated you are, as a rule of thumb, the darker it is the more dehydrated. Here’s a chart below to help guide you but be aware that the toilet water may dilute the colour of your urine!
So to complete the first step of the framework, you want to go into training sessions with pale coloured urine and not being thirsty! Thirst is not a bad measure of hydration status for most of the time, but when exercising the mechanisms that bring about thirst are often too slow to keep up with the water loss.
If you have a session planned and based on urine colour you may be dehydrated then you want to aim to consume around 6-8ml of fluid per kg body weight within the 2 hours before exercise.
For example for myself, a 75kg man, this is around 450-600mls fluid pre exercise.
Preventing dehydration in training
so we’re all set up for pre exercise and step one of our framework has been ticked off. Next step is all about preventing dehydration whilst training, specifically preventing 2% body mass loss from water! To do this it’s a pretty good idea to have an estimate as to how much weight you lose per hour when training. This is when a sweat test can come in handy. All you need is yourself and some reliable scales and you’ll be able to estimate your sweat rate.
Simply weigh yourself before a training session, monitor the amount of fluid you’ve drunk and then weigh yourself after. It’s safe to assume that any weight lost in that training session is from sweat and so you can use the numbers to estimate your sweat rate.
You can then use this information to guide the amount of fluid you need to drink in a training session.
Post exercise, it’s important to try and replenish what is lost, and if excessively dehydrated if excessively dehydrated, it is recommended to consume 1.5L of fluid per kg of body weight loss.
It’s important to note here too that it may not be practical to take in the estimated amount you lose, chugging 1.5L in an hour session is likely going to leave you feeling pretty uncomfortable, with this it would be worth aiming for an amount that is feasible and stops you from losing that 2% body mass we mentioned earlier
It’s important here to not necessarily just use water though, overhydration can potentially become an issue. Hyponatremia is something that occurs when blood plasma sodium levels drop dangerously low. This can happen when sodium has been lost in sweat and not replaced.
Attempting to rehydrate with just water and not replacing sodium can lead to even lower sodium levels, this can then lead to headaches, nausea and in some extreme conditions death. This is why it’s important to consider other aspects of hydration that aren’t just fluid!
Electrolytes are salts and minerals that can conduct electrical impulses, there are a number of these in the body but key ones are sodium, potassium, chloride and magnesium. These electrolytes play a number of roles, some in muscle contraction, others in helping maintain water balance.
They are lost in sweat, and it is thought that a loss of electrolytes like sodium can lead to muscle cramping due to the role they play in muscle contractions. It’s very hard to know without testing, how much of each electrolyte you lose in sweat.
The good news for most of us is that for exercise lasting less than an hour you probably don’t need an electrolyte beverage, but for longer and hotter sessions it could definitely be worth looking into.
Below is a link to a hydration plan that you can use and a quiz from precision hydration, it will help you figure out how high your sodium losses might be and offer advice as to how to get that sodium in!
Personalised hydration plan
First step is to figure out your sweat rate. A simple little test for fluid loss is to weigh yourself before and after a workout.
We can assume that the weight change here is predominantly due to fluid loss and thus you can consume enough fluid to bring yourself back to baseline. Other recommendations include:
Before exercise
Drink about 6-8ml of fluid per kg bodyweight around 2 hours pre exercise
E.g A 75kg man, 450-600ml fluid pre exercise.
If this is water, consider a salty snack. Or go for a drink with carbs and electrolytes in.
During Exercise
Let’s use that sweat loss baby
E.g. A 75kg man PRE Exercise, weighs in at 73.5kgs post-exercise having consumed 500ml water. Estimated fluid loss is around 2kg, let's assume fluid density of 1kg/L, and that I worked out for 2 whole hours….the rate of fluid loss is 1L/Hour. Thus aim to consume around this much during exercise.
This may not be possible due to the sheer volume of fluid causing gastrointestinal upset so a compromise can be made.
It is recommended to include sodium in this hydration fluid if exercise lasts longer than an hour.
Post exercise
If excessively dehydrated, it is recommended to consume 1.5L of fluid per kg of bodyweight loss.
In the example above, 3L of fluid should be consumed to restore to baseline.
AGAIN THIS MAY NOT BE POSSIBLE! It’s about finding the balance between the numbers and the athlete to optimise hydration as best you can.
Tonicity
Outside of electrolytes and water, the type of fluid also comes into play here. We’ve briefly touched upon it a little bit when talking about hyponatremia, but the big word to think about when deciding what kind of fluid is appropriate when is tonicity.
Tonicity essentially refers to the concentration of a solution relative to the blood.
There are 3 types of solution when it comes to tonicity, hypertonic, isotonic and hypotonic.
Let’s look at these individually, and unpack when you’d use them and for what.
Starting with perhaps the most common, isotonic.
Isotonic is a bit of a buzz word in sports nutrition and you see it on sports drinks pretty much everywhere, it essentially means a fluid that has a similar concentration of solutes than the blood. They tend to have around a 6-8% carbohydrate concentration and theoretically, they deliver a reasonable amount of energy and clear the gut promptly. They can be useful for shorter duration high intensity exercise for when carbs are needed potentially a little sooner than hydration! Because of the carb content they can still cause some gastric upset and sometimes the carb contents of certain ”isotonic drinks” are higher than stated so that they become Hypertonic.
Which leads nicely on to hypertonic beverages.
These bad boys are normally formulated with a LOT of carbohydrates and are great for high intensity activities. They deliver a large amount of calories and carbohydrates quickly and efficiently, as it’s easier to chug a coke than to smash a loaf of bread! Alas these beverages are not great at hydrating you. When you drink them, the concentration of carbs in the intestinal lumen becomes so high that water ends up leaving the bloodstream and entering the intestine to allow for absorption of nutrients. This is why it’s best to stick to coca cola when you’re just in the need for energy and NOT for hydration.
Finally we have Hypotonic.
These are beverages that have a lower concentration of solutes than the blood. This means that the water in them is absorbed into the bloodstream faster than the other solutions. But because of the low concentration of solutes and carbs they do not deliver a huge amount of fuel. These are perfect for when hydration is the goal. Most solutions used for rehydrating are designed to be hypotonic but with a small amount of carbohydrate and electrolytes in them to ensure you replace electrolytes and don’t end up suffering from hyponatremia!
Final thoughts
So there we have it! Your one stop shop to hydration, the key points we want you to take away from this are ultimately that dehydration is BAD (duh) and should be avoided at all costs, to avoid dehydration you ultimately need a personalised hydration plan that follows a 3 step approach around being hydrated before training, hydrating sufficiently during the session to limit water losses and then to replenish what is lost afterwards!
Don’t forget the importance of electrolytes and remember when which tonicity of beverage is useful and you can’t go too far wrong.
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