Hydrating

When exercising we sweat, even if sea swimming. Sweating is essentially dehydrating. Sweating is a very individual thing. Heavy athletes, athletes going fast or hot conditions will cause higher levels of sweating whilst lighter athletes, athletes moving slower and/or cool conditions will cause 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 salty sweaters. Using the information set out here, you can make an informed assessment on 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 water and salt, mainly. 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. Sweating less than 1l/hr is regarded as 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, try remain within 2-4% of your original body weight in order to maintain performance. That said, drinking without the salt added could be very dangerous. Spend some time getting dialled in with how much salt you need in your water so it is close to fine art on the day of your endurance challenge. 

Approximately 1000mg of sodium per litre of water is average for most athletes. To gauge how much table salt to add to your water, 1000mg sodium looks like just under half of a level teaspoon of table salt.

At the lower end, the not sweaty athletes would need close to 500mg/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 and could assume the correct amount of sodium per hour based on how much of a salty sweater you are - note that in the winter you are likely to lose more salt/l water and in the hotter summer you will actually loose 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 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 salt.

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

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

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

There are some devices coming to market that you can wear to measure how much salt is in your sweat. However, it isn’t known to be completely accurate so the better estimate would be the breakdown above. That said, in the very near future it is likely that a device like this could be very accurate and helpful. Once you know your salt water ratio, it is unlikely to change. There is some really useful information on the Precision Hydration website (but they don't mention you could use table salt and water). 

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 = 1litre of water - but don't forget to account for the weight of water and energy you take on during. 

Example: you weigh yourself at 70kg (weighed naked). You do a race pace effort for 1hr on the bike and consume 1L of fluid, no food. After the session you weigh (naked again) yourself and you are 69kg. You need to account for the 1kg you added to yourself by drinking the 1L of fluid so you have basically sweated 2kg, that's 2L of fluid per hour. Two hours in similar conditions at that intensity would require 4 litres... Use the five categories from above to assess how much sodium in the range of 500-2000mg per litre you need. 

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

If you are still always unsure on how much fluid you will need due to an unknown ride or weather conditions for example, you could split the two by taking on salt tablets and drinking pure water separately. This could be usful in hot conditons when a little more water could be usful. Or cold conditions when additional salt is better. But be carful to always have both. If you have a good idea of how much water you need you could add an electrolyte tablet or some salt to your water. Proper electrolyte tablets tend to contain a very small amount of potassium and calcium which you also loose in sweat and and the loss contributes to cramping and fatigue so if hydrating with water and table salt, consider these micronutrients in your fuelling.

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. Do not allow yourself to get too thirsty, it will bring on fatigue!