Years ago I used to run regulary, then I switched to biking exclusively. After an unpleasant and fairly weak century ride this weekend, was thinking maybe I needed to switch off with running again - that my routine pleasure rides just don't provide enough intensity for serious conditioning. So, I went to gym and ran for 40 minutes today, almost effortlessly. I was amazed how easy it was and thinking it must be due to all that riding.

So, has anyone studied mixing running with biking as part of overall training regime, or the benefits of one over the other? Would you say running is the rough equivalent of doing intervals or more agressive riding, but otherwise they are fairly equivalent in terms of getting the benefits and conditioning? Or, is it an apples and oranges comparison?