RG3's underwater treadmill
Interesting story about the underwater treadmill that RG3 is using for rehab. It's an interesting idea, you get the running motion but with less weight on the knee. Buried somewhere in the story, the company claims that Adrian Peterson used one for rehab last year, which is pretty significant if true (I don't have any reason to doubt them but I don't think Peterson has publicly said he used one).
These are actually very common and have been around for a long time. They even use them for animals, there being three of them to treat injured dogs in the Atlanta area.