Suspends body vertically in the water at shoulder level for an effective, low-impact workout. Resilient, closed-cell foam won't absorb water, dries quickly and resists chlorine-damage. Patented, contoured design supports and strengthens lower back. Narrows at waist for comfort and freedom of movement. Features quick-release buckle and custom-woven elastic belt. Tones abdominal muscles due to continual use of abdominal muscles to maintain correct posture