With the longer runs, my right foot has started hurting about 4 miles into the run. When my foot hits the pavement, it starts with a sharp, mild pain in the ball of my foot that travels down the outside as the rest of my foot hits the ground. It stops hurting a few minutes after I stop running/cool down. I haven't noticed it when I run during the week - only on the longer weekend runs. Any ideas? I'm a 31 year old woman - about 5'4" and 155 lbs. - running about a 12 min. mile.
Thanks!

Runnin Round,
I would guess that on the weekends you are trying to keep up with a group of friends and you are lengthening your stride. This may be irritating your plantar fascia. Try shortening your strides during your long runs. Stop by the tent and have a doctor look at your foot.
Cheers,
Dr. Jake