I was also a runner from my days in the military. Used to be my medium of choice to deal with stress and stay in shape. About 4 years ago, I started having trouble with my achilles tendon. 3 years ago, after spending 4 weeks in a boot and applying nitroglycerine topically to the area, I had the tendon surgically repaired. That was the end of my running days. I am now prohibited from running, jumping, or performing any high impact activity. Cycling was one of the few options left, and one that I very much enjoyed. Consequently, I've become a cyclist. I try to ride every day. And I notice no ill effects on my repaired achilles tendon.