Best way to measure sweat rate and sodium loss?

Nutrition
1

Any tips on calculating sweat rate and sodium loss?

I seem to ride best when I am chugging 40 oz per hour and getting good sodium. Even in mild weather I am dripping and everything is salt crusted.

I don’t sweat much when not exercising though.

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2

After being frustrated for years and knowing my sodium/hydration was off, I finally did a proper sweat test:

It’s been about 1.5 years and their recommendations have been spot on. Previously I was consuming about 500mg of sodium per hour when I actually needed 1100mg per hour. Additionally, during hot/humid races I was drinking 24oz of water per hour when I actually needed 1+ liters per hour.

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4

This is false particularly related to endurance athletes.

Dr. McCubbin and Costa found no relationship between the change in sodium intake and the change in sweat sodium concentration.

…as long as you’re not doing anything extreme - like completely starving yourself of any salt intake whatsoever (very difficult to do!), or consuming a crazy amount of salt like 9,000mg a day - then your sweat sodium concentration is highly likely to remain relatively stable and it certainly won’t deviate far enough away from your baseline level to warrant any major changes in your hydration or nutrition strategy.

5

I noticed that sweat testing is done to detect cycstic fibrosis?

I think I will ask my doctor to set me up with a test (won’t be insurance covered but that is OK.)

6

Precision Hydration has instructions on how to measure your sweat rate, so you could start tracking that on a spreadsheet.

For sodium loss, I really wanted to try their sweat test, but the closest location is an 8-hour drive away for me, so I ended up trying these Levelen sweat tests. It took a couple weeks to get the results back from the lab, but the tests were pretty straightforward to do and gave me a reasonable ballpark to start experimenting with sodium intake. I’ve been using those figures and the ones from the sweat rate spreadsheet to track my sweat and sodium loss in various conditions for future reference. If it helps, here’s my spreadsheet, if you want to make a copy.