Purpose: Thoracic extension and hyperextension are prominent features of elite butterfly swimmers. As an elite butterflyer breathes, they often hyperextend their thoracic spine which decreases frontal drag. Directions: Simply, put a double tennis ball on the thoracic spine and gently rock back and forth on the ball. This will mobilize the thoracic spine in extension. Perform ten mobilizations at one segment, then move up, towards the cervical spine.