Under-water balance boards were developed for physical therapy and are used also for recreation. Besides the general advantages of aquatic therapy over non-aquatic therapy (the use of the smooth resistance of water instead of the jerky resistance of weights and the avoidance of burdening an injured joint with excessive weight– in this case, the weight of the patient's own body), aquatic balance boards have the specific advantage over non-aquatic balance boards of saving a patient who slips off of a board from the impact of falling and crashing into a floor. Slipping off of an aquatic balance board is safe as long as the user knows to avoid inhaling while underwater and knows how to tread water.