Hygenic's opposing resistance training Thera-Band Aquatic Dumbbells have foam ends and are lightweight but once you get into the water, you will be shocked with the resistance needed to move the weights underwater for an effective aquatic workout. A swimmer incorporating these Hand Bars can tone and strengthen muscles as well as increase range of motion, strengthen lower back, increase back flexibility and strengthen their core abdominal muscles. Water resistance also preserves joint wear and tear.