Sorry that I wasn't more descriptive earlier. I have been running track since 7th grade. I seriously injured my quadricep in a hurdle accident in HS. I also tore my achilles tendon while doing the triple jump 2 yrs ago. Plus I have the unfortunate gift of getting the genes for bad knees. It isn't at the point where I am going to give up running. I was just recommended by my Dr. to take it easier and find something that isn't so bad on my kness. I was up to running like 50-60 miles a week, so I want to cut that down in half and take up biking. Hope this clears up the issue.