Nike Free Run (the morning after)

It's the morning after my first run on my Nike Free Run plus. The balls of my feet are tender, nothing major but I can feel they got a work out. I don't remember ever feeling this with my other shoes. I also feel some tenderness in my lower back muscles. No big deal, well worth the experience. It will be interesting to see if my body builds these muscles over time. Also, to be fair I did run six plus miles three times this week. Each run I ended with sprints on the artificial turf field. Full speed one length of the field and jog back to the other end. Continue this over and over for a mile or so. I can't wait to try the Free's on the rubberized 1/4 mile track. That track is a joy to run on, soft and fast! It has been covered in snow for months, snow is gone now.