some people can do cardio in water if they flare on land. you can walk/run along the bottom or exercise suspended above the pool floor.

you could build muscle strength by lifting weights in water. (water resistance only, foam or actual weights depending on the exercise). i still flare and am very limited but for example if i were to try to do say a bicep curl i can fine tune it to how i feel that day by adjusting the resistance of my hand against the water. on a better day i could keep my fingers closed and on a more flared day i open my fingers (less resistance). its helpful to get initial direction from a pt or similar so the posture is correct.

what i wonder is why many TOSers can jump and do extensive cardio on land while others cant take the force.