This is my first post on the Fitness page. I'm doing Mark's beginner exercises, slowly. Most of my exercise is just walking. I walk about a mile 3x a week. For the past 1.5 weeks I haven't walked at all, the weather's been bad, so I've stayed indoors.

Today I went out to walk and only made about 1/4 mi. The tendons on the outside and lower inside of my right leg got really sore very fast. I wore the same tennis shoes I always do. I've never had sore tendons before. What causes it? And what should I do? I'm 75 and don't exercise a whole lot anyway but I do like to walk.