My husband has a long term health condition. Until 18 months ago he was active, climbing, kayakiing, working. Now he struggle to walk. More then 30 mins will mean he has to have a sleep. On a bad day he cant,t walk 10 mins. Last time he tried swimming he struggled to maitain his head above water. (despite being a white water kayaker.) What excercise/ ways of being active can he do. He is getting fat. (To be blunt.)