I finally understand where this myth is coming from. John Walker of The Hacker’s Diet (and so much more) is the source. Under “What, Me Exercise?” he lists various activities and the calories burned. Bicycling gets 300/hr while jogging gets 700/hr. Now, if you don’t put out any effort and spend a lot of time coasting along, then, yes, you may as well walk for your exercise. The Final Sprint offers this:
The standard comparison is that one mile of running equals four miles of cycling, but that’s lousy science. Although running requires the same amount of energy per mile at any speed (110 calories per mile), riding is affected by wind resistance so the faster you ride, the more energy you use. So you have to compare running and cycling at different cycling speeds.
Which makes a ton of sense. Now, take this “activity calculator” and compare 90 minutes of cycling at around 13mph (~1100 calories) to 90 minutes of running at 6mph (~1400 calories). We’re not accounting for hills here (which changes things considerably) so this doesn’t reflect the actual number of calories being burned on my ride, but it’s a good estimate. Still, the comparision of 1400 to 1100 isn’t quite as dramatic as John Walker’s chart would have you believe. It is only a quarter more calories instead of double the amount. Come on, people! Trust, but verify! The Hacker’s Diet is a great resource, the excercise portion, at least, has some funny numbers. (I know, he probably got his numbers from somewhere else and that source is wrong, but two people I know who’ve read John Walker’s book have claimed running burns “a lot more” calories than cycling, so I suspect the book is the source of their misinformation.)