Inspired by the other thread about sprinting. I have only anecdotal stories, but for the past few years I have been training for running both track and cross country. During the summer months while building a base for cross country I ride/race mountain bikes. I am training for the 8k, and I am coming of a track season where I focus on the 800/1500.
I started when I was young and wasn't particularity fast, in both running and cycling, but as I improved as a runner, I could ride bikes way better. I can defiantly say that cycling has improved my running and vice versa. I really only have one benchmark race, which is a 40 mile mountain bike race that I have consistently done for the past 6 years. The first few years that I competed, I didn't see much improvement. This previous two years, I have gotten a lot faster as my times dropped in running. Last summer I competed the race in 3:30, with very little riding and a very strenuous running schedule. That week of the race, I still ran 50 miles.
This year I took some time off in the winter, so I am getting back into the swing of training, I think that I won't race too much this summer.
Does anyone else train for biking by running more that biking? Once I start getting into more competitive races I assume I will not have the same success.
Running helps me with my base and sprints can help with LT and LA clearance, but to be serious about cycling, running should probably be minimal.
OTOH, running keeps my weight down better than cycling, which helps my cycling as much as riding Lightweight carbon wheels.