If you’ve ever had an injury that made it difficult to walk, you may have discovered that putting weight on your bad foot or leg is much easier if you’re standing in a pool. That’s because the buoyancy of the water supports most of the body’s weight and counteracts the effects of gravity. Less weight on the injured limb means less stress on the joints, which translates to less pain.

A special anti-gravity treadmill at Miami Orthopedics & Sports Medicine Institute’s outpatient rehabilitation center in Coral Gables essentially does the same thing, and more — not with water but compressed air.

This treadmill, called the AlterG, is helping many physical therapy and rehab patients regain mobility faster, more easily and more comfortably. After the patient is zipped into the treadmill at the waist, air is blown into the airtight compartment. The physical therapist can control in 1 percent increments what proportion of body weight the patient is bearing — from 20 percent to 100 percent. Then the patient can walk, limp-free, or even run.

See the video here.

“We treat a wide variety of patients with the anti-gravity treadmill,” said Luke Buech, a physical therapist with Miami Orthopedics & Sports Medicine Institute. “Athletes with injuries such as ACL tears, ankle sprains and hip injuries; and older people who are recovering from hip and knee replacements or injuries.”

The benefits are many. For people recovering from injuries, surgery or joint replacements, the anti-gravity treadmill gets them walking sooner — and that weight-bearing activity helps in their recovery. “The muscles will get stronger faster,” Mr. Buesch explained.

Walking on the anti-gravity treadmill also results in a more normal gait. Some people return from an injury or surgery with a limp, which can cause problems to other joints and become chronic.

“If they limp too long, it’s hard for patients to break bad habits,” Mr. Buesch said. “This is a very healthy way to start training the limb.”

For a young competitive runner like Julia Villena, 18, the anti-gravity treadmill allowed her to maintain her fitness while she rested a painful left knee. The treadmill’s built-in video also allowed Mr. Buesch and Ms. Villena to evaluate her foot placement, gait and stride.

The use of the anti-gravity treadmill was part of the physical therapy prescribed by Keith Hechtman, M.D., orthopedic surgeon with Miami Orthopedics & Sports Medicine Institute, after an imaging scan showed that Ms. Villena’s knee cap was shifting higher on her leg than normal, which was likely caused by weakness in her hip and hamstring. Shortly after the track season began in her senior year at St. Brendan High School, she had to slow down.

Mr. Buesch put Ms. Villena on the AlterG after she had rested her knee for several weeks and had done therapeutic exercises to strengthen her hip. She started out jogging at 50 percent of her body weight and, over a few weeks, worked up to running at 70 percent of her body weight. “It’s pretty cool,” Ms. Villena said during one session. “I can run without pain.”

The middle distance runner is set to attend St. Thomas University in the fall on an athletic scholarship. She plans to focus on cross country competition and major in nursing.

“It’s always nice to keep an athlete moving,” Mr. Buesch said. “I didn’t want to shut her down during her season. This allowed her to stay at the competitive level.”