Proper ankle mobility helps reduce injuries, particularly in the lower legs. But poor mobility can also cause the overloading of muscles up the chain as well. To perform the ankle mobility test from Jay Dicchary’s book, Anatomy for Runners, sit in a chair with your feet flat on the ground. Then slide your hips forward while keeping your feet flat on the ground. If you can get your knees out as far as or just past your toes without picking your heels up off the ground then you have adequate range of motion.
If not, you should spend some time stretching your lower legs after your runs. Dicchary recommends stretching your calves on a slant board or rolled up towel for at least 2-3 minutes at a time in order to increase the length of the tissue. Shorter periods of stretching or active mobility can be helpful for increasing range of motion in an acute sense, but research shows that to actually lengthen the tissue it’s best to hold the stretch for a longer period of time.