Do your knees hurt every time you break into a trot? If so, Walter Dandy's RunBike may be for you. It's a modified bike frame that carries about 1/3 of your weight while you get a cardiovascular workout.

A 210-lb. runner can head down the road putting just 130 lbs. on his shoes. Users say it's like running on a trampoline.

Dandy created the RunBike for himself in 2001 because running had just become too painful.

To get into the RunBike, you drop the frame sideways and step in, connecting up the rubber harness. "It takes much longer to put on your running shoes than it does to get in the bike," Dandy says, noting that you don't need to wear any safety equipment.

While the bike steers itself about 95 percent of the time, you steer it like a bike for sharp turns. Dandy says he doesn't know of anyone falling in it because your feet are always on the ground.