I’m a runner, and I’m always having to take grief from people (especially my wife) who happily point out that you’ll get the same benefit walking three miles as you will running the same distance, and you won’t risk crippling arthritis of all your major body parts. So the other day I had a flash! Going back to high school auto mechanics and some hot-rod magazines, I explained to my wife that since I’m exerting the same force to move the same mass the same distance, I’m doing the same amount of work–but since I’m doing it twice as fast, I’m exerting two times the power and probably using twice the calories. My wife is pretty bright, though: she pointed out that if I run and exert twice the power in half the time, and then sit on my butt desperately trying to catch my breath for the other half of the time, then average power exerted is a wash. Is she right? Does running have any calorie advantage over walking, or am I really being that dumb (not like it would be the first time)? –Peter Prout, Winchester, Virginia
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- However, this assumes that running and walking are equally efficient means of locomotion. Generally speaking they’re not–running requires substantially more energy per unit of distance. Several factors contribute to this. Shall we start with entropy and the second law of thermodynamics? Eh, maybe not. How about aerodynamic drag, which increases with the square of the speed? Probably not something you need to worry about unless you’ve really been hitting the steroids. Here’s something a little more relevant: Analyses of the biomechanics of walking v. running suggest that walking is a more efficient gait except at higher speeds. The crossover point is somewhere around five miles per hour, varying with the individual. At that speed, walking and running are equally efficient. Below the crossover point, running is less efficient, apparently because you lose energy absorbing the impact of the ground with your bent knees. Above it, walking falls behind because of the awkwardness of the racewalking gait. Gait is the critical issue, incidentally–running speed is irrelevant. Subtracting out the energy required just to keep you breathing, you’ll use about the same amount of juice finishing the marathon in two hours or four.
Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.
