With walking, the effort by the ankle extensor muscles (shin muscles, pointing the toes up) is twice as much as the knee extensors muscles (quad muscles) and 25% more when running. Without strength in those ankle extensor muscles we lose ankle mobility. Without ankle mobility our knee extensors must activate more which adds additional stress on the knee. Ankle strength is the key to maintaining ankle mobility and in keeping optimal biomechanics. Without it, injuries increase and performance suffers!