Originally Posted by Happy Feet

Paraphrasing for emphasis.
I totally agree with this. The machine takes away much of the auxillary action of dynamically maintaining balance, countering and supporting more weight upright.

On a bike (unless one is standing and mashing) the weight and balance is supported by three points (hands, pelvis, feet) and not thrown that far off of the COG (center of balance). Running, all weight and balance is supported by the feet only and many muscle groups from there up have to act to maintain balance while the body is thrown farther off of its COG.

How that is expressed specifically is up for debate I suppose but it demonstrates the main sentiment expressed that running gives a more intense workout in a shorter time.

Per hour spent in the activity I find recovery time from running greater because it is higher impact. For example, when cycling commuting to work I ride one hour per day. This I can do indefinitely. At my age, if I ran one hour every day I would soon need a recovery period. As it is I alternate cycling and trail running to achieve this effect.