Very good question! My guess is your shoes, are they high tops? If not, then my suggestion is to make a change in your shoes. Also, there are some exercises that you can do to help strengthen your ankles before and after your hike. For instance, depending on your balance, stand flat footed and rock up onto your toes and back down, and repeat this several times, then there's something else you can do is, before and after your up and down exercises, sit and just roll your feet in circles one way, then the other several times!!