This exercise is similar to swimming except for the fact that it is not done in a pool. It basically focuses on your lower back, strengthens it and makes it firm so that you stand tall.
You can start off by lying down on your stomach on a flat and firm surface. Stretch your body to the maximum extent. While resting your chin on the floor, stretch your arms out in front of your face with your palms facing downwards. This should be the starting position. Now raise your right arm a few inches from the floor and lift your left leg off the floor simultaneously without bending your knees, as far up as you can. Maintain this position for a few seconds and then come to the starting position. Repeat this process with your left arm and right leg. This exercise helps in toning the lower back and prevents slouching. A toned back can stay upright and make you appear taller.