" How does lifting weights enhance running economy and endurance? Other studies have shown that it works by increasing the stiffness of the leg when the foot hits the ground (Dumke et al. 2010). The legs function as springs during running. Physics teaches us that a stiffer spring loses less energy when it lands and bounces higher. Your legs will do the same thing if you strengthen them in the gym. "

― Matt Fitzgerald , Racing Weight: How to Get Lean for Peak Performance