Comment by bagacrap

wouldn't efficiency correlate to effort? pretty sure the "effort" is the feeling of burning calories. If an elite athlete can run for an hour and burn 2000 calories in that time, they will beat a less elite athlete who can run for 1900 calories in an hour, all else equal. Put them on bicycles or a rower and they'll be able to burn the exact same number of calories (assuming sufficient training in the target exercise medium) because the limiting factor is their body's ability to process oxygen, not the exact form factor of the exercise.