Hydrating

When exercising, we sweat, even if sea swimming. Sweating is essentially dehydrating. Sweating is a very individual thing. Heavy athletes, those moving quickly, or those operating in hot conditions, will experience higher levels of sweating. In contrast, lighter athletes, those moving more slowly and/or in cooler conditions, will exhibit lower levels of sweating. Of course, you could be somewhere in the middle (for example, a light, fast runner on a moderate day).

There are also individual differences. Some people are salty sweaters, whilst others are not. Using the information set out here, you can make an informed assessment of how much hydration you may need for your endurance training and challenges. I'm aiming to give you the option to stay fully hydrated for less than a penny per session (but you can spend lots more). Read on...

We sweat mainly water and salt. This means that hydration should contain both water and salt. The Ironman University suggests that the mode fluid loss per hour at IM intensity is between 1 and 1.5 litres. Still, of course, the temperature and location of the race makes a huge difference. Based on the same advice, sweating less than 1 L/hr is considered low. Sweating more than 2L/hr is considered high, and more than 2.5L/hr is very high! However, replacing exactly what you lose during the training session or race is not necessary. Instead, aim to maintain a weight within 2-4% of your original body weight to optimise performance. That said, drinking without the salt added could be very dangerous. Please spend some time dialling in how much salt you need in your water so it is close to fine art on the day of your endurance challenge. 

Approximately 700-1000mg of sodium per litre of water is average for most athletes. To gauge how much sea salt from your kitchen to add to your water, 1000mg of sodium is just under half a level teaspoon of sea salt. If you use sea salt rather than table salt, you also get a trace of key electrolytes such as magnesium, potassium, and zinc, which is much better for you. 

At the lower end, the not-sweaty athletes would need about 500 mg/L. At the upper end, the salty sweaters would require 2000mg/l. You can make a good guess as to how salty a sweater you are by looking at your clothes after training and racing. You will fall into one of the following categories. You could estimate the correct amount of sodium per hour based on how salty a sweater you are. Note that in the winter, you are likely to lose slightly more salt/l water, and in the hotter summer, you will actually lose slightly less salt/l water.

·       Sweating buckets - drenched and covered in white salt after a race or hard, race effort session, of over one hour - have 2000mg sodium p/l or a teaspoon of sea salt.

·       Pretty darn sweaty - still drenched in sweat, less white and salty than the saltiest sweaters though - have 1500mg sodium p/l or 3/4 a level teaspoon of sea salt.

·       Fairly sweaty - not completely drenched but wet all over - have 1000mg sodium p/l or 1/2 a level teaspoon of sea salt.

·       A bit sweaty - a sheen of sweat all over - have 750mg sodium p/l or 3/8 a level teaspoon of sea salt.

·       Not sweaty - people can't really tell you have been exercising - have 500mg sodium p/l or 2/8 a level teaspoon of sea salt.

Some devices, such as the Gatorade GX sweat patch, are available for measuring the amount of salt in your sweat. However, the breakdown above will get you close. Once you know your saltwater ratio, you just need to know how much fluid you need at a given environmental temperature and exercise intensity. Bear in mind that your body can adapt to sweating more or less at a given temperature, but your salt ratio will be much the same.

As the amount of fluid (water with the correct amount of salt in) needed depends greatly on conditions (how hard you go, for how long, how hot or cold it is etc.). To estimate how much fluid you need, it is worth doing a sweat test in training. Weigh yourself before and after - 1kg = 1 litre of water - but don't forget to account for the weight of the water and the energy you take on.  Plug the numbers into the CALCULATOR to see how much body weight you lose and the correct rehydration rate. The key thing with this test is to do it often, all the time if possible, to build up a picture and track your hydration needs.

Keep drinking throughout your training sessions and races. Drink the fluid to thirst as you go. Use sea salt or buy more complex electrolyte tabs to add. But get the amounts dialled in first.

As a general rule, to go with right away, for every athlete, male, female, heavy, light, fast, slow, etc. I suggest taking your water bottle and simply adding a big pinch of salt. Drink to thirst. Please do not let yourself get too thirsty; it will make you feel fatigued!