Originally Posted by PeteHski

I only mentioned elliptical because I happen to have one that measures power output accurately. It's not exactly running, but it is weight bearing, which seemed to be your main argument for running expending more energy.

Nobody is arguing that bicycles are not faster than running! But that doesn't mean energy expenditure is necessarily less per unit time when cycling. As I said earlier, minimum energy expenditure is likely to be higher when running (you can't coast and walking doesn't count as running). But maximum energy expenditure is basically how many watts you can possibly output over a unit of time (not distance). Now I know for sure I can output a higher power on a bike vs running. I've measured both (or at least elliptical vs bike with the same power measuring system). So I expend more energy riding a bike than I do running for any fixed length of time. Of course I will cover much more distance on the bike in that time, but that wasn't the question posed. Or at least that's not how I would interpret it. I presumed the question was all about energy expenditure over a given time duration at maximum effort. If the question really was about energy expenditure over a fixed distance then it's pretty obvious and doesn't warrant any discussion.

Using more muscle groups doesn't necessarily expend more total energy. It all depends how hard those muscle groups are working. For example I use more muscle groups walking than when cycling. But I can easily expend more energy cycling regardless of using less muscle groups.