How Many Calories Are You Really Burning?
I got an e-mail from a reader recently asking about the relative calorie consumption of biking versus running. Using typical calculators like the Compendium of Physical Activities, he felt as though there was a big mismatch in effort between the two activities for a given rate of calorie burning. This is a pretty common complaint: nobody every really believes the calorie estimates produced by cardio machines — and with good reason. I wrote a guest post about this topic a couple of years ago for Yoni Freedhoff’s blog, Weighty Matters, and I decided to revisit it for my Globe and Mail column this week.
I looked at three factors that can make your personal calorie consumption deviate from the “average” values you get from cardio machines or online calculators: body shape, fitness, and heat. Two interesting points:
– people with more body fat burn fewer calories (per kilogram of total body weight) than average;
– people with greater aerobic fitness burn fewer calories (per kilogram of total body weight) than average.
This may seem like a contradiction, but it’s worth remembering: fitness and fatness are two different things, though they’re often related.
As for the reader who asked about cycling versus running, the most useful thing I found was this 2005 paper from the University of Cape Town. They looked at estimated energy expenditure based on heart rate for submaximal exercise (basically below lactate threshold), and found that calorie consumption had a linear dependence on heart rate — and interestingly, the same relationship appeared to hold for both running and cycling. This implies that if you cycle at the same heart rate that you run, you’re burning roughly the same number of calories (again, as long as the effort is aerobic). The same relationship doesn’t hold for exercises where you’re too far from vertical, or submerged in water, both of which lower your heart rate.
That’s what the research (at least, that one study) seems to suggest. Does this make sense? I don’t have enough experience cycling with a heart-rate monitor to have an intuitive feeling of whether it’s true. Does perceived effort on the bike and on the run match up at similar heart rates? Anyone have any insight to offer?