Pool therapy can be very helpful in a rehab program. It unloads the joint while strengthening the muscles. The legs become nearly weightless while still getting resistance. Pool therapy helps reduce swelling while encouraging greater motion with less pain.
An underwater treadmill works best for someone who has had knee surgery. There is a down side to water therapy. The drag of water may change the way a person walks. Muscles aren't activating the way they would on dry land so the training effect isn't quite the
There's no harm in asking your friend to consider water therapy as an option. A doctor's approval may be needed. Pool therapy may have to wait if there are stitches, staples, or open wounds of any kind.