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A buddy and I have been debating the caloric expenditures of running hills. After a little research it seems there is a reasonable discrepancy out there about just how much "work" is done when running up and down hills.
There is a an old-school formula out there that most treadmills and exercise calculators use that take your calories burned at a given pace and multiply that by the grade (or incline) to get the marginal increase or decrease in running hills. For example:
[kcals @ 5% incline @ 7mph] = [kcals @ 7mph] + [kcals @ 7mph] x 0.05
To me it seems this equation has a few shortcomings and assumptions:
- Assumes that the relationship between CALORIC EXPENDITURE and GRADE is LINEAR. So going from 20% grade to 25% grade is just as hard as going from 1% to 6% grade.
- Assumes that running downhill is easier than running uphill, and to the SAME DEGREE. So running downhill 15% is just as easy as running uphill 15% is hard. Weird double speak I know.
- BOTTOM LINE IS that if you run in a loop at a steady pace all your uphills will cancel with your downhills and you get no calorie calculation credit for any "hills" that are in the loop, no matter how big. I think most can agree that a hilly run is almost always SLOWER and harder than a flat run (we should get credit!)
What they found is very complex to interpret, however Figure 1 seems to make it most clear to the "rest of us":
- The increase in calories burned going uphill DOUBLED when the grade increased by only 20% (for example going from 10% to 30% grade energy expenditure went from 5 to 10). By the traditional calculation our calories burned would've only gone up by 20%, rather than 200%.
- When running downhill, energy expenditure seems to follow the traditional rule until we reach about a -17% grade. At this point it actually gets HARDER to run downhill than uphill.
So the net result of all this is that when running in hilly terrain we are burning far more calories than our old-school calculators are telling us, even if we run in a loop where the uphills "cancel" the downhills.
To go a step further I took a 1 mile loop near my house where I run up (and down) a big hill. Using the traditional calorie calculation I'd burn about 130 kcals (based on weight and steady pace). If I add in the corrections for hills from this study it bumps my calories up to 220 (about 70% more; note that doing this calculation was tough and used excel, I will spare you for now).
So the challenge is twofold: 1) repeat this study a few more times under varying conditions to validate it, and b) change the fitness calculator world to account for this.
A third challenge is underway and might just be patentable, so I will hold off on unveiling it for now.
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