PAgal - your situation may be different to mine, but I'll tell you what my doc told me.
When I was complaining that I HAD to lift my 2 year old, and the floors weren't going to vaccum themselves....he doesn't even want me to vaccuum.
He says that SCH weakens the amniotic sac, and it's very important to do as little, lifting, bending, squatting etc because, worst case scenarios are, A. Under pressure the blood could get under the placenta, and cause a placental abruption, or I could have premature rupture of membranes, due to them being weakened, and my baby could be born much too early to survive, and under about 24 weeks there would be nothing I could do, they wouldn't try and save it, I would have to just hold him or her until he/she dies.
Now... I take what he says very seriously, I don't care if I put on a few extra pounds, I am resting as much as possible, and eating heaps of protein (supposed to strengthen the sac) until this crisis has past. He is hopeful that it should resolve itself by about 20 weeks.
I think getting a bit out of shape, is worth the sacrifice, but if it ment that much, and I had to pick an excersise to do, I would pick swimming, as it is very gentle and there is less force of gravity
Sorry I hate to sound like the drama queen.. but that speech certainly put things in perspective for me, quicksmart. Maybe wait until you've had your appointment? You may not be in such a serious position, and gentle excersise might be ok.