Sweat Test - 2PorNot2P

[Deleted User]

Just wondering about the protocol and interpretation here.

For my 2+ hr trainer ride today I did the following:

Empty bladder, weigh in at 167.5lbs (scale only accurate to 0.5lb)

Rode 2hr 10min, drank 3.5x 24oz bottles = 5.25lbs + 2 GU gels (negligible)

Weighed in again at 167.5lbs

Emptied bladder

Weighed in again at 166.5lbs



On the one hand I ended at same weight and was hydrated enough to have to pee.

On the other, apples to apples post urinating I'm down a pound so perhpas needed that extra 1/2 bottle?



Not a major issue over 2hrs but concerned it could lead to a more significant deficit over long course.

Eventually I can test that later in the season but wondering how to adjust now, if any.



Thanks for everyone's 2 cents!

Mark Maurer

David, it sounds like you nailed it. The same thing happened to me last year when I did my sweat test, i.e., I weighed the same after as before. So I continued to take in fluids at the same rate that I did on the test and it worked fine for me. I would also weigh myself before most long rides and then again afterwards just to check things. It's a little more tricky that way especially since there's usually some food involved and perhaps a nature stop on the ride, but if it's close then I don't worry about it.

The other factor that you mentioned was the scale being accurate to 0.5 lbs so you could be off by +/- so the 1 lb difference after peeing could actually be 1.5 lbs or 0.5 lbs.

Mark Maurer

David, it sounds like you nailed it. The same thing happened to me last year when I did my sweat test, i.e., I weighed the same after as before. So I continued to take in fluids at the same rate that I did on the test and it worked fine for me. I would also weigh myself before most long rides and then again afterwards just to check things. It's a little more tricky that way especially since there's usually some food involved and perhaps a nature stop on the ride, but if it's close then I don't worry about it.

The other factor that you mentioned was the scale being accurate to 0.5 lbs so you could be off by +/- so the 1 lb difference after peeing could actually be 1.5 lbs or 0.5 lbs.

tim cronk

David, Factoring in the couple variables you lost roughly 2.5 lbs per hour so that puts you at 1.5-1.75 bottles per hour...Sounds reasonable and a good place to start... You dont always have to do an official test but like Mark said its not a bad idea to weigh before and after a ride do a little math just to check things... I have a friend who sets up a transition in his driveway for the brick run when done riding which includes a scale... Bit anal but its easy enough to do... Things to keep in mind going forward are how similar the sweat test conditions were to race day specially if on a trainer ? Temperature, Humidity , Wind (fans) , and Intensity are huge variables.... Many people will do a much higher intensity ride on a trainer with negligible cooling effects than they will ever do on an IM and get a much higher sweat rate!

[Deleted User]

Thanks guys -

As I've mentioned elsewhere here, this is something I'm going to be measuring, adjusting, learning, etc throughout the season as last time (IMWI 2011) I totally blew it.

Seems like I'm at a good starting point for now but to Tim's point, will need to get a better sense of how to adjust for various conditions. WI was much hotter than expected and I underdrank my plan, not to mention didn't really adjust it for the hotter temps in the first place.

Thanks gents.

Shaughn Simmons

David, for a long course event also consider how much sodium you are losing per hour based on your sweat rate and supplement your fluid intake if applicable using only buffered electrolytes like Salt Stick...

salty sweat

high sodium sweat losses can further increase your risk of developing hyponatremia. fit and acclimatized triathletes usually have less than 900 mg of sodium per liter of sweat. while higher sodium sweat losses are usually seen in unfit and unacclimatized individuals, some highly trained triathletes may be salty sweaters with losses exceeding 1400 mg per liter. if one of these salty sweater triathletes also has a high sweat rate, their losses multiply and they can lose significant amounts of sodium during a half or full ironman triathlon. while lab testing indicates that sodium losses range from 460 to 1800 mg sodium per liter sweat, chances are your only indicator of high sodium losses is white salt rings and streaks on your clothing and skin.

clearly salty sweaters need to replace sodium losses to maintain safe blood sodium levels. even dehydrated triathletes can develop hyponatremia if they have high enough sodium sweat losses over a long race. look at the sodium content of the sports drinks, gels, and other products that you consume during racing. some triathletes will need to veer closer to higher sodium sports drinks, and others may even want to carefully supplement with sodium tablets. salt tablets should be stored in a waterproof case or bag to prevent disintegration and should be taken with eight ounces of fluid. generally one or two salt tablets per hour is sufficient (amounts per tablet vary). excess salt intake without adequate fluid intake could irritate your stomach, and result in bloating and nausea. experiment with these products in training. high sodium sports drinks are probably the most convenient strategy and also provide fluid and carbohydrates when racing.

http://www.usatriathlon.org/about-m...42109.aspx