It takes a lot of practice. I just got back to trying to run. I can bike well and swim but running has always been difficult. I've had a broken back and broken hip which might come into play, but even when I was a kid it was hard. I think it takes more time to build up to. I have seen a difference in my strength from when I first started and biking in between helps. I'm not fast but going for longer periods of time is encouraging. Form is definitely important. I watched an ironman recently and one girl set a new course record for the run. When you watched her, she took really short, marching type steps. My husband introduced me to this and it helps.