Medical device maker Alter-G, has an interesting concept for physical therapy: Anti-gravity. Based in Menlo Park, Calif., it offers a special treadmill, called the G-Trainer, that uses air pressure to give patients the feeling of weightlessness as they are moving. And it just landed $8 million in second-round funding to continue growing its operations and market penetration.

The anti-gravity environment is said to allow patients to extend their range of motion while taking strain off joints and other potential injuries. For these reasons, it can also be used to enhance normal performance, not just treat existing damage, the company claims.

Currently targeted at athletes, the technology — which can “lower” body weight to 20 percent — is in use in several collegiate, sports and fitness programs in the U.S., Europe and Asia. The company lists NCAA teams at Stanford, USC and UC Berkeley among its clients, as well as the Arizona Diamondbacks, the Golden State Warriors and the Oakland Raiders.

The investment round was provided by Versant Ventures. It raised $2.5 million in first-round funding last June from Frog & Peach Investments, Astrolabe Ventures and Funk Ventures.