Geospace Air Kicks Anti-Gravity Running Boots; Multiple Sizes - Small, Medium, Large Available in Small, Medium, or Large sizes depending on user weight Comes in Black and Red (Small and Medium Size) or Gray and Blue (Large Size) New, improved wider boot design is ergonomically shaped for comfort. The new AIR KICKS model is adjustable to fit right over virtually ANY SIZE athletic shoe, including YOUTH 2-7, WOMEN 3 - 15.5, MEN 6-14. Powered by patented JUMPING JAX T-Spring technology, which utilizes heavy-duty, rubber T-Springs to capture and then transform downward energy into longer, low-impact strides that are gentle on the ankles, knees and back. Extended range of Replacement T-Springs available (sold separately) for changes in user body weight.