This reminds me of the "good cyclist" thread. There is more to it than aerobic capacity. Obviously, a strong runner will have an advantage over a more sedantary person when starting cycling.
The problem I have seen is they have the ability to go fast before they have the matching bike skills.
A very strong and competitive runner I knew crashed himself out of the sport soon after switching to cycling with a brain injury. Several others, friends of mine, have had similar problems. Horrible crashes by men who were very strong but had limited cycling experience.