Despite standard care, 25%-50% of patients with clots in the deep veins of the arms and legs progress to chronic post-clot problems resulting in significant disability, loss of productivity, and healthcare costs. Reverse flow in the veins from an organizing clot is the primary cause of post-clot problems. Veins with early clot breakdown have a lower incidence of reverse flow. The investigators have observed that clot breakdown is enhanced by increased blood flow and that moderate arm and leg exercise result in increased venous blood flow. Hence, the investigators predict that a supervised exercise program in patients with deep vein clots could increase leg vein blood flow, accelerate clot breakdown, and decrease the risk of post clot problems. The primary hypothesis is that increased blood flow across the clot (induced by supervised exercise) will increase clot breakdown and decrease severity of post clot problems. The investigators are conducting a randomized clinical trial of standard therapy compared to progressive exercise training in patients with leg deep vein clots.