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1228mg/l – The sodium content in my sweat. What does that mean and how do I use it to optimize my hydration and salt intake strategy?

200mg/l is the lowest measured and 2300mg/l is the highest, with an average of 950mg/l. It puts me in the middle of the category high in regards to sweat content. How many litres I sweat per hour is another crucial factor and duration of the effort the third.

With this knowledge, I can much more accurately estimate the needed salt intake during races and longer training efforts. We do not need to replace the lost salt in a ratio of 1-1, so there is normally no need to take salt in sessions lasting shorter than two hours.

Duration is the easiest factor to predict with high accuracy, at least for an experienced triathlete like me with roughly 30 Ironman distance races completed. For others it might be less accurate predictions so have a buffer in your plan in regards to salt. It does not hurt run performance to carry a few more salt tablets than needed when crossing the finish line. Having too few salt tablets can definitely hurt your performance.

Sweat rate is trickier than the looks of it. Testing your sweat rate is easy:

1. Measure your weight before a training session without clothes
2. Measure your weight after a training session dry without clothes
3. Record the fluid intake, duration of the session and if you pied during the session (300ml is a good average estimate of a pie if you are not willing to measure it).
4. Use this information to calculate how much sweat you lose each hour.

Note that you can also do this on your local gym if you just bring a scale. If you weight your training clothes in both dry and wet conditions on a kitchen scale you don’t need to get naked in front of everybody 😉

What makes the estimation of sweat rate more complicated is obvious; it varies hugely with intensity, air temperature, humidity and sun vs cloud. At maximum sweat rate, I peak at around 3 litres/hour. If the conditions are colder it can be 1,2 litres/h for the same effort. Testing the sweat rate in different conditions is the only way to find out. More about sweat rate testing can be read in this blog post by Precision Hydration, which includes a spreadsheet to help you do the calculations.

Knowing the salt content in my sweat + an good estimation of my sweat rate + the duration = good hydration and salt intake strategy.

Looking back at my previous races and the salt intake it is clear that my intake was too low. About 500mg sodium each hour in hot races (typically two salt capsules each hour) as recommended by the suppliers of the salt capsules, always from well-known brands. In a race like Kona that would be an intake of 500mg/h x 9 h = 4500mg. If I estimate an average sweat rate of 1,5 litres/h with would a total fluid loss of 13,5 litres. With my sweat salt content that would say a total sodium loss of 13,5 + 1228mg/l = 16578mg. A total deficit of 12078mg(!).

With this knowledge I increase the intake to 1500mg/h in hot races, mixing PH1500/H2Pro1500 in my water, with the aim to drink 1 litre per hour during the bike. During the run, I will eat SweatSalt capsules at the rate of 6 per hour. In colder races, I will still use PH1500/H2Pro1500 in my water, but with less water intake it would also mean less salt, matching up to a lower sweat rate and net total salt loss. 4 SweatSalt capsules per hour would probably be sufficient.

Optimizing your hydration and salt intake is a never-ending process. The most important thing is to start with a good plan, execute the plan and adjust according to the outcome.

Do you find this interesting? There are many places you can perform an advanced sweat test and the list can be found in this link. If you live in Norway and would like to have a test please let me know. Currently, there is no possibility to perform such a test, but if the interest is high enough we can get a sweat rate machine.

If products from Precision Hydration looks tempting you can always use the promo code ALLAN15 to get 15 % off your order.