- Is that what happens when you work REALLY HARD on one day??? Your - weight goes up???? You're kidding...really????
Yes, that's what happens. When you work out, you lose water by sweating, causing your body to dehydrate. Muscles are one of the places your body stores water, so they dehydrate, too. (Dehydration can also be caused by other things than working out, such as sauna, ovulation, kidney problems or just not drinking enough.)
When you drink after of during the workout, the water goes to rehydrate your dehydrated muscles. However, your body likes to play it safe, so it will not only replenish the water you lost but add some more.
So instead of just passing through, some of the water you drink after a workout will remain in your body, and obviously affect your weight. So even if you burned, say, 5 oz of fat during a really hard workout, your body might retain a litre of water, and next morning you might weigh 2 lbs more than the day before.
Luckily, water retention is not a bad thing. The excess water will come out in a day or two.