Yesterday it was around 80 degrees and sunny. I ran for 10 miles, most at around 6:45 pace with 4 miles at 5:30 pace and I ended up losing 8 pounds. To me that seems like a lot, but I don't know, this is the first time I've really been keeping track of my weight.
I'll lose anywhere from 1-2 pounds in sweat for every two to three miles (or 0.3 to 1 pounds per mile), depending on how hot and humid it is. Mind you I'm only 5'7" and 145-147 pounds. I imagine sweat rate would be different for everyone, and might vary with height and weight, I dunno.
I'm 6'5" and was 163.5 after my run yesterday. Don't know if that helps.
What you want to pay attention to more than the amount of weight that you lose is whether or not you gain it back by the next run. It's ok to lose 8 pounds, but you need to make sure to get hydrated again after.
Varies a great deal among individuals. Two guys we had as subjects, were of same height and weight and both raced a 25k within 1 minute of the same time under the same conditions. Both also consumed 1 liter (2.2 pounds) of fluid during this race. One ended up weighing 8.8 pounds less at the end of the run and the other weighed 3 pounds less. You should keep your own log of pre- and post-run weights during various runs under different weather conditions; this will give you an idea of how much to drink during runs. ACSM says to try not to lose more than 3% of your body weight, but that may be a conservative amount for many runners. That heavy sweater I referred to above lost 5.5% and was still feeling OK. However, at his sweat rate (and not consuming more than he did), he probably could not have completed a marathon -- he was losing fluid at a rate of 200 ml per km of running, or 1 liter every 5k. In a 42k race that's 18 pounds, but of course he could replace several pounds of it during the run.
I lost 9 lbs on a 90 minute run. I usually lose about 5 lbs an hour working out but will lose a little more if the workout is very hard.
As you get in better shape, your sweat rate will go up which will allow you to dissipate heat better and run faster for a longer period of time.
As said before, just make sure you rehydrate back to your original weight before your next workoout.
I drop 5-12 lbs depending on the run. I sweat like a pig and put it right back on after drinking enough.
rippy cripple wrote:
As you get in better shape, your sweat rate will go up which will allow you to dissipate heat better and run faster for a longer period of time.
I have to disagree with the sweat rate going up as you get in better shape. I used sweat rediculous amounts just sitting around doing nothing. Then I lost a bunch of weight, and I run much faster; now I sweat about a quarter of what I used to. It would make sense to sweat less if you have less mass to cool off.
For me, it also depends strongly on how heat-acclimated I am. In the spring when it starts warming up, I sweat like crazy; after maybe a month I'm back down near my cool-weather levels. In spring, I can lose 10 lbs. on my long run, but then I had a run last summer where I went for 2 hours in 96F heat, felt fine, and had water left over at the end.