I'm not sure if this will help while you're in a cast, but if you're looking to get stronger while you're rebuilding your hand/grip strength I would look into isolator fitness (isolator fitness.com). Theyre known for their meal prep bags but they make gear that literally allow you to do virtually any lift without use of your hands. This is only relevant really if you're looking to build muscle strength and mass that goes beyond your grip strength or if you've lost use of your hands due to injury, etc., and while I've always wanted to try them I haven't had a good enough reason to take my hands out of the equation. It costs quite a bit and you'll attract a lot of attention but if it's worth it to you at least you know it's an option. Good luck!