I have leiden's factor v. I had a DVT in my thigh two monthsago. I take 8mg Coumadin (warfarin) daily and adjust it per my pt. Cani use treadmill for 1 hour per day, pretty fast?

Yes. Keeping fit is important. Swelling can be an issue. If no swelling and no pain, keep it up. Swimming can be a good and better exercize due to position and no dependent legs.
Check with Dr. The answer depends on the size and location of the blood clot and the chances of it breaking off and traveling to the lung. Swimming and walking are safer alternatives until the clot in your leg completely dissolve and anchors to the wall of the vein. Check with your doctor.