Theoretically, if I exercise 3,500cal off per day, will I lose 1lb per day?

It would definitely be unhealthy to exercise that much -- that's like running 35 miles a day! In running a marathon (26.2 miles), athletes generally "hit the wall" at around mile 22 -- that's because the body can only store about 2,200 calories worth of glycogen for energy. People eat during races in order to have their glycogen replenished. But it would defnitely be unhealthy to stay in such a glycogen-depleted state, and you'd have a massive buildup of the stress hormone cortisol -- which, oddly enough, causes the body to store fat. Having too much cortisol would probably reduce the calorie burn too. Interesting question though.

Theoretically you have to have a deficit of 3500 calories to lose a pond - that is 3500 calories less than you body needs depending on your metabolism, etc. If you eat enough calories to make up for the exercise, then you wouldn't lose the weight. And doing 3500 calories worth of exercise in one day is a LOT of exercise!! The most I have ever done in one day is probably about 1500 calories worth of exercise, and I found that was really pushing it for me.

I do understand your frustration. It seems to take so long to lose the weight. Try decreasing your caloric intake a little and also drinking more water, lots of water. Making these two slight changes in addition to the exercise may speed up the process.

For me eating an orange or two everyday seemed to speed the process along - they are high in water and fibre with relatively low calories and they suppress hunger and are high in nutrients.

The two links I've included may be helpful to you. They help keep me on track. Good luck with it.

If you could keep up that level of exercise, I guess so. But I think that probably you'd start losing muscle and really harming your body.

Don't forget that building muscles increases your base metabolism. The more muscle you have, the faster you'll get thinner. Notice I didn't say "lose weight" because muscle is more dense than fat. (Eventually you will lose weight as well.)

That's the theory, but it depends on your calorie intake as well. You could also build muscle. Don't forget water weight either. The scale is deceiving.