How does hydration impact our bodies
Hydration is the process of causing something to absorb water. Our bodies store water in two different compartments; in our bodies cells, which gives them size and structure, and in the blood.
Water in the blood is particularly important for athletes - we need blood to be circulating when we’re training to fuel our muscles, take away waste, and dissipate heat. If you start a training session well hydrated it maximises blood volume, which will reduce fatigue and help you maintain performance for longer.
Put simply, training performance is influenced by how hydrated you are. Similarly, so is recovery. Without enough fluid the reactions in the body slow down, impacting the rate at which your muscles recover and tissues heal.
What is sweat?
We have a lot of water in our blood plasma and that is where sweat comes from. Sweat serves as the body’s coolant, protecting it from overheating.
As humans we’re exceptionally good at losing heat through sweat. The more we sweat the more water we need to consume. When we start sweating during training we’re in a fighting battle against fluid and electrolyte loss.
Sodium is the main electrolyte we lose when we sweat. It is an electrolyte that plays an important role in fluid balance in the body - and therefore our performance. Sodium helps maintain your blood plasma volume by signaling to your kidneys to retain more of the fluid you consume.
Every person loses sodium in their sweat (sometimes we see salt on our skin) but individual differences vary, it can be up to 10x difference. Your body can’t make or store much sodium.
If we have a small sodium deficit post training that’s fine, we’ll probably replace that through a balanced diet. If we sweat for a long period of time we run the risk of diluting our sodium levels down. This results in a contraction of plasma volume and we may need to replenish it through supplementation.
Sweat is an important element of our physiology, which if understood can help us create more effective hydration strategies. Everybody sweats at different rates, due to a variety of factors. The important thing is to understand your body, how it responds to training, and take note of what happens.
There are two things to understand
What is your sweat rate? Are you a light, medium or heavy sweater?
What is your sweat concentration? How much sodium (salt) do you lose in your sweat?
How can we measure our sweat rate and concentration?
If you want a basic idea of your sweat rate and sodium concentration you can take note of the following over a period of time and start to spot patterns:
How much do you sweat during a training session? Take note of the type of session, how hydrated you were going into it, what the conditions were etc.
For sodium levels, how salty do you think your sweat is? Do you get white marks on your clothes, stinging in your eyes, crusty sweat?
Think about previous problems you may have had with hydration. Any muscle cramping, dizziness or do you struggle to perform in the heat?
If you’re interested to know more you can do a scientific sweat test, check out Precision Hydration, or use their spreadsheet to calculate your sweat rate more accurately by weighing yourself pre and post training (1kg lost = 1 litre of fluid).
What to do with the data?
There is simplicity to the 1 litre out 1 litre in, however 100% sweat loss replacement hasn’t been proven effective. It often requires drinking beyond the body’s natural thirst instincts, which can be dangerous.
Our bodies can tolerate quite a bit of dehydration during training, providing we went in well hydrated. The exact amount you need to replace is individual, and will likely vary day to day.
What might impact your sweat rate?
Body size - the bigger you are the more you’ll sweat
Fitness response - the fitter you are, the better developed your sweat response, therefore the more you sweat
Exercise intensity - the faster you are moving the more quickly you’ll sweat
Metabolic rate - the higher your metabolic, the more you’ll sweat
Environment - temperature and humidity will have a big impact on your sweat rates
Acclimatisation - if you aren’t used to heat then your body will have a bigger sweat response