Interesting posts in this thread.
As to the Garmin's efficiency:
Originally Posted by
HoustonB
...the exertion level is likely to be slightly over 1,000 calories an hour.
Originally Posted by
HoustonB
To the other poster referring to the Garmin device that computed 3,500 calories for a 3 hour ride - that thing needs some serious calibration.
Isn't 3500 calories / 3 hours somewhat close to 1,000 calories/hour? I'm also 245lbs and just getting into cycling, so I think my body probably isn't so efficient at burning calories yet.
Reason I got the Garmin was to help tone down my workouts and spend more time in the aerobic zone as opposed to the anaerobic to improve that efficiency.
BTW, here's the ride it said I did 3728 calories:
http://i23.photobucket.com/albums/b3.../heartrate.jpg
As to how efficient a bike is over a runner:
I say this is highly dependent on the bike, speed and elevation changes on the bike ride. I can cruise a 45mile ride on the flats at 13-15mph and feel like I hardly worked out (helps to have a nice bike). As for running, I would be completely destroyed if I ran 9 miles right now at a 9:00 mile pace - assuming I could even do it.
Just think about the physics of a high end bike with 100psi road tires, it hardly encounters any friction/resistance traveling 15mph on the flats, so it only takes a small amount of energy to keep it going - it's the miracle of the wheel. Running on the other hand, every time your foot hits the ground you're back down to 0. Increase your speed and climb rate on the bike however, and the resistance goes up exponentially.
So essentially a bike has a much wider range of efficiency than a runner. That is to say, it can either be much more efficient than a runner (9 times?), or only slightly more efficient(3 times?) depending on the factors mentioned above.
Therefore, I think we can say that both Zephyr's and Matchka's examples are accurate.