I stretch in the pool as I find it easier, even working on sitting straight in a bath tub with legs relatively straight will stretch you back and glutes a bit , after a long period of shoulder injury I'm trying to get more flexibility, knee is problematic currently due to job and overweight. Maybe the swimming has aggravated it I don't know more likely kneeling and ladders and mostly stood up all day at a bench for 20 years. Did a extremely short weight session which was demoralising, found I couldn't curl due to elbow and definitely couldn't start a squat due to knee , so sauna bit of swim an