Often, PTs will talk about your knee moving in a “valgus” motion. Valgus is basically the scientific term for being knock-kneed—or having knees that collapse inward mid-stride. Valgus movement puts a ton of pressure on the knee, and is thought to be one of the main causes of patellofemoral pain. While weak glutes and hips can cause the motion, “A flat, over-pronated foot can also cause your knee to collapse into valgus,” says Chao. “Working the small toe flexors in the arch of the foot can help make sure the ankle stays neutral,” he adds.
In bare feet, sit on a chair with your feet resting flat against the floor. “Mash the arch into the floor. Then try to hollow your arch or lift the middle of your foot off the floor without moving the heel or the toes from their position on the floor,” says Chao. ”This is a tricky one that takes some careful control,” he warns, so take your time with the exercise. Hold the hollow for 5-10 seconds before lowering back down and repeating, Aim for 20-30 reps on each foot.