This is my first post on the forum, and I wanted to start by thanking Steve and Scott for the fantastic resources they are making available. I don’t think there is anything else out there that teaches recreational / amateur athletes the science behind training in such a clear and methodical way and it has certainly been eye opening for me.

My question concerns the “transferability” of one’s aerobic fitness over different activities. Or to put this another way, the extent to which the aerobic capacity one has in one activity (e.g running) overlaps with the aerobic capacity one has in another (e.g. cycling). I ask because running is my main sport, but I cannot do more than a few miles a week currently owing to a knee injury. I am able to cycle however and am enjoying going out on long Z1/Z2 rides. Ideally I would like to build up my base through cycling, while slowly increasing the running milage as my knee recovers – so that my running engine is much the same as before I got injured. But I was wondering how much crossover there is – i.e. whether there is ultimately a cap on the benefit I can get training this way, so I would be better off waiting and building up running-specific fitness as my knee recovers.

Any thoughts would be much appreciated.