I have a deep venous thrombosis near my subclavian vein. what risks do i run when i work my arm too hard?

Probably not much: The clot inside of your subclavian vein should be quite sticky unless it is very new. The chance of dislodging the clot with exercise is not zero, but is very small. The consequence of working your arm may be more swelling which will improve when you raise your arm above the level of your head.

Subclavian DVT: Anticoagulation reduces chance clot will travel, but what was cause? Do you have a central venous catheter? Are you a weight lifter? I am concerned that you may have venous thrombosis from vein compression from thoracic outlet syndrome. Treatment for that may include dissolving clot (thrombolysis) and possible removal of the first rib and Anticoagulation Suggest vascular surgery consult.