Spring-loaded shoes are running shoes that have very small, lightweight springs embedded in their soles. The springs act as shock absorbers when runners' feet hit the ground and provide additional uplift in each step.
Developed at the University of Central Lancashire, spring-loaded running shoes were designed to protect runners from the shock waves their legs experience each time their feet hit the ground. Shock-related injuries affect 70 percent of all runners every year, including inflammation of the knee, shin splints and stress fractures.
Adidas brought a shoe designed with the same principle in mind to market in 2013. Rather than using actual springs, the sole of the Adidas shoe features forward-angled blades made of a highly reactive polymer that compresses and releases energy with each step.