Have been a runner since 1971 and have used running as my primary form of exercise. Had to have my left knee scoped in 95 and was able to return to running. Had 12 good years till 2007 when the same knee needed more work. I took that as a sign the I needed to run less and increase my bike riding. After the knee operation I started riding my DF as my exercise. Several months the discomfort lead me to a recumbent which I have been riding since August 07. I've gotten my 'bent' legs and am enjoying the increased distance that is possible on the recumbent.