Spira shoes are a brand of shoe where titanium springs (WaveSpring® Technology) are embedded in the sole of the shoes. The springs are light and small enough that the shoe soles do not look different than any other shoe.
With the springs in the sole, energy that is otherwise lost to ground forces is returned. Many say they immediately feel less pain or stress in the knees and back as well as in their feet.
Another benefit of the Spira shoes is that when the shoe has a spring in the forefoot (some styles only have them in the heel), the shoe acts as a non-flexible forefoot shoe. Shoes that do not flex in the forefoot are of benefit for those with arthritis and other issues at the 1st metatarsal joint.
Image: Spira.com