Sports sweatpants to help you run faster
Put elastic strips on the outside of the knees and ankles of sweat pants. This will store some of the energy when you land as you are running, because when you hit the ground your knees and ankles flex. Then it will be easier to take the next step. The contraction of the elastic would help you push off from the ground better, because you extend your knees and ankles to push yourself off the ground to take your next stride. You should be able to run faster. It might also take some of the strain off your knee and ankle joints, because it would cushion your landings.
It would be important to anchor the sweatpants in place so they don't ride up or down as you run. You could anchor them below by making them fit over the foot like a stocking and anchor them above with suspenders. You also wouldn't want to make the elastic too stiff or the person couldn't bend their legs properly. If you could just store maybe 40% of the energy when they hit the ground in the elastic it should be enough to make it significantly easier for them to push off the ground for the next stride.
Reward: A pair of these sweatpants