In this studio, I wanted to create something that would allow people to run faster and more efficiently, while also being conveniently portable and unpowered. I came up with two ideas for how to do this, and worked on the first in the previous studio. In this studio, I worked on the second idea. This is a modified cast which uses leaf springs to capture energy when the wearer is about to push off the ground and release it for the push off. When running, there is a small amount of negative work for the ankle when the runner shifts forward past the foot, causing the ankle to unflex. Then there is a large amount of work for the ankle when it must flex to push the foot off the ground and propel the runner forwards. The leaf springs capture this negative work by resisting when the ankle unflexes, and push back when the ankle flexes. They are designed to only resist when the ankle unflexes past a 90 degree angle with the leg, and thus do not strain the wearer when they are standing.