When using this waterpower bag when exercising you will immediately feel the unforgiving properties. The entire weight of the water swishing back and forth in the response of a slight tilt as you may be trying to raise above your head will even cause your smallest muscles to begin working together as your larger muscles are forced to work harder to maintain balance. This device can humble the most avid trained athlete. . Come visit our store to see more. Make sure to use the code FIRSTORDER for a 10% discount.