Purpose: Many short axis swimmers have excessive lumbar lordosis, a likely indicator of weak anterior sagittal plane core strength. This exercise encourages a position of maximally strengthening the anterior sagittal plane, when performed properly. Directions: Have the swimmer lie on their back with a foam roll under their knees and their arms holding onto a heavy medicine ball or bench. Next, have the swimmer posteriorly tilt their pelvis (contract their abdominals) and bring their knees to their chest. Make sure the swimmer doesn't excessively round their upper back while bringing their legs up or arch their lower back as they lower their legs.