When your foot strikes the ground, the functional stability of the whole kinetic chain relies on a strong and agile base. Yet that base is often neglected in training routines. And while calf strength is important, stretching and mobility are critical as well. “The whole complex needs to work together all the way up the totem pole,” says Nicole Haas, a board-certified orthopedic clinical specialist with a doctorate in physical therapy. If you have stiff ankles or calves, or significant lower-leg asymmetries, that could reverberate up the limb and cause pain in the knees, hips, and back, as well as limit your performance.