Andy did promise he'd be posting pics of funny outfits during his rehab so perhaps this is the first in a series.
I'm sure it is. Can't wait for more.
Also doing gentle exercises in water will be very good for his back, which is why hydrotherapy is frequently used to treat a variety of conditions where joints and/or muscles are involved, especially painful ones, because
When submerged in a body of water such as a bath or a pool, there is a kind of weightlessness, as the water relieves your body of much of the effects of gravity. Water also has a hydrostatic effect and has a massage-like feeling as the water gently kneads your body, while water, when it is moving, stimulates the touch receptors on the skin, increasing blood circulation and releasing tight muscles.
Also the water will be warm. Many years ago I used to go what passed for swimming in nearby baths, and always went on the day children suffering from celebral palsy had been for therapy earlier. Lovely!