When the forefoot can rotate properly and invert the force pushes your knee outward and lifts the arch from collapsing. Most individuals in western society have very weak intrinsic foot muscles and poor forefoot rotation from wearing shoes and walking on flat surfaces. Our foot was designed for contour and mobility, not shoes and flat floors so as a result most have feet are very weak. This simple exercise is designed to strengthen forefoot inversion and supination. When a foot is weak it collapses into what is called pronation and often arch support are given which only makes the problem worse. Strengthen the foot not buttress the foot.