A spoonful of sugar

We talk about the energy efficiency of walking but do we ever stop to think just how energy efficient we are? There are various calorie calculators on the web that allow you to work this out. ExRx.net is one. Type in a comfortable walking speed (5km/h or 3mph) and you’ll find that someone weighing about 70kg uses up 250 calories per hour. That works out at 50 calories per km. It’s even less than this if you subtract off the energy that we would have used up if we had simply sat still for that same length of time.

Then compare that with the calorific values of some foods. A level teaspoon of sugar contains 15 calories and a heaped one 25 calories. Walking a kilometre thus takes two heaped teaspoons full of sugar. This really does suggest that leisurely walking really isn’t a particularly effective way to lose weight. Not eating two teaspoons of sugar has got to be easier than walking a kilometre. There are 140 calories in a standard 330ml can of coke so that’s fuel for about half an hour’s walking for an adult.

Of course the numbers rise as you get faster but not by that much. 7 km/h (4.4 mph) is a very fast walk but you are still only consuming 60 calories per km – 4 level teaspoons of sugar. You do get more kilometres covered in a given time though so the rate goes up to 420 calories per hour – three cans of coke.

Another way to put these figures into context is to compare the efficiency of walking to car travel. The average car has a fuel consumption of about 10km per litre and a litre contains about 8,000 calories. To drive a km thus takes up about 800 calories, about 16 times the amount it takes to walk the same distance (although the car is considerably heavier and you do go a bit faster!).

Anyway I hope the point is made. Walking is really efficient. When we are thinking about the biomechanical mechanisms underlying walking the real question is should not be “Why does it cost so much?”, but, “How can it cost so little?”

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