I'm currently resting my ankle, was doing circuit training and went over on my ankle. Put down to a twisted ankle and thought nothing of it and cracked on with things. Month later and still having trouble, went to the Dr's and found out I have strained the tendons and I need to stay off it for a week or 2.
Ouch! Fortunately it was just over-use in my case. I think it was doing a fast paced 2 miles on the treadmill then a 3 mile run around town 20 minutes after which caused it (in new minimalist shoes which I wasn't used to!)