Originally Posted by
Happy Feet
Cover a set distance running or cycling. Your use more energy doing the former. That's it.
Distance is the wrong limit to impose, unless you're determined to make riding look as if it's a less energy-consuming workout intrinsically, which it is not. As has been pointed out repeatedly (and patiently) in this thread, ride and run at a rate of 200 watts for an hour, and you'll have used the same amount of energy.