So last night, prior to 12 mi run, I weigh myself. Then after run I weigh again, and find that I lost 9.5 lbs. This was in 92*F, about 49% Humidity, and took 1:26 at 7:12 pace.
Is this much loss normal? Is it fair to assume that this was all sweat loss. How should I turn this into data to help with nutrition planning for longer events like 1/2IM?
Yes, I lose 6-8 on a 10 mile run in hot weather.
Holy moly. Do you drink at all? (I never loose more than 2-3 pounds.)
Alex
Ok…but how to make good use of this? Should I try to turn it into lbs per hour of sweat loss and convert to oz? How much can your body replace in an hour?
In my experience, I can drink and absorb up to 32 oz per hour.
Alex
In my experience, I can drink and absorb up to 32 oz per hour.
If I run a 7 miler and drink about 16oz of water at the midpoint I could get back to my house and be anywhere from 2-4lb dehydrated. Of course I’m running in a sauna here in Floriduh, but it’s critical for me to drink a lot on long training runs. I make sure that I stop by my house to step on the scale every 10 miles (or 50ish on the bike) to keep track of hydration. If I am more than 2-3lb down I’ll stop for 5 minutes and rehydrate. I find on the bike I can drink a full NXT bottle (32oz?) every 10-12 miles and that keeps me on track for a normal finishing weight for any distance. 64oz per hour on the bike…that’s a LOT of sweating!
“64oz per hour on the bike…that’s a LOT of sweating!”
i recently had my sweat rate measured on the bike. HR never got above 130. temp was 85. humidity about 60. sweat rate was 68 oz/hour.
on long bike days (4-6 hour rides), i end up having to stop and hydrate for 10-15 minuts about every 2 hours. either that or i have to ride really really slow.
If you sweat a lot (I do), that’s probably pretty normal.
I did 5m easy this am, it was cool (mebbe 70) but very humid, and I lost 3 lbs (factoring in the 16 oz of water I drank beforehand, but after weighing myself) in 37+ mins. So that’s approx 48 oz of sweat. Yuk.
I’d recommend that for runs longer than say 1hr in the heat and/or humidity, that you invest in an Amphipod or Fuel Belt (or Camelbak, or waistpack, or whatever works for you) so you can carry some water with ya.
You don’t hafta replace every last drop of fluid during a run or ride, just make sure the deficit doesn’t become too large, because that’s when performance can start to decline. If I had to drink enuff to cover my actual fluid loss during exercise, I’d get a hernia carrying all of that water.