I was also a competitive runner who had to stop running due to injuries (although I am much, much older than you ) When I first started to cycle, I wasn't that thrilled about it. In fact, I was angry because my real passion (running) was "taken away from me" and I was forced to find another physical activity to take its place. But the more I rode the bike, the more I fell in love with it. For me, it's probably the only activity that comes close to replacing my real love - running. Hopefully, your stress fractures will heal and you will run again someday but until then...enjoy your bike! If you're like me, you'll find that the transition from running to biking is pretty easy. The few times that I've tried to run, I feel like a slug Have fun with it!!