Purpose: Improving posterior chain strength (glutes and hamstrings) helps increase strength in muscles used during breaststroke, as well as on the start in turn. These muscles also protect the knee during breaststroke, making posterior chain strengthening a staple for knee injury prevention. This is an advanced exercise, only perform if you are progressing from the double leg back extension exercise. Directions: With your partner holding the back of on of your ankles, drape your body over the end of a couch or sturdy table so that your legs are straight and secured. Make sure the neck is in a neutral position and your arms are in the mummy position. Bend at the hips and not the spine, getting a good stretch in the hamstrings. Raise the torso while squeeze the glutes to lockout.