Has anyone been tested to learn their actual sweat rate and then used that info to tailor their hydration - quantity and type - needs? I would like to hear about your experience and how this helped you.
I am consistently losing a ton of fluid from sweating, even in cooler weather (but high humidity) and then cramping. I would like to get some scientific testing to determine how much and what types of fluid & supplements that can help me overcome this.
Also, any idea how much you sweat when swimming in a wetsuit in 70degree water for a 70min swim? Trying to learn how much I am fluid I am losing when I the water prior to getting on the bike.
Weigh yourself naked before and after a workout. The difference is sweat loss. Repeat for all sports and under a variety of conditions and you will have a good idea where to start for hydration.
If you’re looking for simple volume lost, you can do what the previous poster suggested. I did it all summer and found it was fairly consistent when graphed on a simple temperature-rate graph. When measuring, don’t forget to record the current temperature and humidity. Knowing you lose 500mL/hour when it is 10C out doesn’t tell you anything about your performance at 35C. I also found it varied widely between sport to sport.
Interesting points:
-Apparently the highest recorded rate is around 3.5L/hr
-I got up to 2.5L/hr on some hot days
-When you’re expecting to lose 2.5L/hr, it’s really hard to plan enough hydration for a 70.3. It’s hard to find 5L of space on a bike frame.
-Somewhere I found someone claim the stomach can only absorb 1L/hr of fluid
If you’re looking for quantities of salts lost, that’s probably much harder to figure out. Even if you got it lab tested, you’d have to get tested at various levels of exertion, distance, temperature, etc to get a full picture of your electrolyte loss in a given environmental situation.
Edit: You could maybe determine electrolyte mass loss by somehow collecting every drop of sweat lost in a workout, then measuring what’s left behind after it evaporates. You could maybe accomplish this on a trainer on a rubber mat. It’d be something like:
0) Weigh yourself naked
Full-on sodium analysis, which I learned about at the eLoad booth at Interbike this weekend. You courier in a sealed sweaty patch, and they come back with your concentration details and a recommended sodium intake plan.
Edit: You could maybe determine electrolyte mass loss by somehow collecting every drop of sweat lost in a workout, then measuring what’s left behind after it evaporates.
I’m interested in getting more quantitative about hydration/nutrition also since I went to the hospital w/hyponatremia after my last half. Now wrt the collect sweat idea, I’d suggest taking a few samples during a workout and then measuring the conductivity. I just did a quick search and saw some conductivity probes for under $50. That’d be much easier and more accurate. Even better using ion chromatography, although one of those may be harder to come by and more pricey
Weigh yourself naked before and after a workout. The difference is sweat loss. Repeat for all sports and under a variety of conditions and you will have a good idea where to start for hydration.
This except don’t drink, eat, or pee between weighings. You can load up on fluids beforehand. An hour workout should be no trouble to get in without drinking.
My sweat rate doesn’t vary much between running and riding, moderately warm weather (85 and medium humidity) I go almost exactly an ounce a minute. Hard to take in that much without gut issues on long course.
Right. If you take in fluids during your workout count those. I.e. if you weight the same before and after a 1 hr session, but drank a 24oz bottle, you sweat rate is 24 oz/hr. The hard part is remembering not to pee before you weigh when finished.
Thanks to all of you. In my last IM I lost 13lbs from weigh in the day before to med tent after the bike so I clearly have some issue going on. I will review all of these links. I hope to determine not only fluid but somehow figure out the amount of sodium, potassium, etc to take it to compensate for the loss.
