Deep water is the perfect environment for a nonimpact cardiovascular workout. But it’s also a great option for flexibility and strength training. Because of this, deep-water exercises are popular with everyone from elite athletes looking for cross-training to people rehabilitating injuries or suffering from chronic illnesses such as fibromyalgia and arthritis. Because the exercises are done in water that is over your head, some sort of flotation device is used to keep your head above the water. Along with equipment for flotation, special equipment to enhance resistance is also used for deep-water exercise.