before you go trying magnets, try ice for the first 24-48 hours, then use heat on your injury. I have two reusable icepacks that can be microwaved and used as heat packs also. They come with their own stretchy velcro bandage. You can get them at any pharmacy/drug store. Great for anything that ails me after a tough tennis match. Sure it's not as magical as magnets, and you guaranteed not to see unicorns while using them, but they work for me, and countless other people in sports.
When somebody gets plastered in football, you don't see them getting in a magnetic closet do you? No, they use ice.