Long distance runners who run outside on hard pavement are particularly prone to overuse injuries such as plantar fasciitis and Achilles tendonitis. Runners who experience these types of overuse syndromes are often forced to stop running until the injury heals which can decrease their fitness level. Fortunately, there's an alternative way for runners to get a good workout that won't aggravate their injuries. It's called deep water running, and, and the name implies, it involves running in deep water.
Deep water running is performed by putting on a flotation device and running in deep water such as a pool in much the same manner as running is done on the ground. While wearing the flotation device, running movements are carried out using short, fast strides. The water adds resistance which increases the intensity of the workout, yet the legs never touch the ground, so injured limbs aren't stressed. Just as on land, deep water running can be done at a controlled, sustained pace; or interval training can be used where periods of intense "running" are mixed with slower, recovery periods. Most deep water running coaches say that people who run in water regularly increase their speed on land.
There really are few disadvantages of deep water running other than the fact that you need to find a pool with deep water and it can be inconvenient to get wet. Although the heart rate doesn't increase as much with deep water running, the workout can be just as intense if interval training is done. It can be used by runners who aren't injured as a way to add diversity to their workout and reduce the wear-and-tear of running on hard surfaces. Deep water running can seem more tiring at first due to the water resistance, but over time the body adjusts and water running becomes easier.
You only need access to a pool and a flotation device. One of the most popular devices is the AquaJogger which keeps you suspended at shoulder height in deep water. Some community colleges and many YMCA's have pools that the public can access for swimming and "running". Always start slowly and gradually work up to longer and more intense intervals. Many world class runners use deep water running as a break from their regular running routine. It's a nice alternative to have available when the joints and tendons need a little break. Keep this form of exercise in mind as a way to challenge yourself or simply to rest sore, aching feet and ankles.