Eric's Arcana and RiderX

It’s not uncommon for people to ask how many calories they burn per mile, and if you do a few web searches, you’ll find numbers in the 35-50 cal/mile range.

Or rather, you’ll find *estimates* in that sort of range.

The problem being that the amount of calories you burn depends drastically on how hard you are riding. And if you are riding for 30 miles, you could get anywhere from 1000 calories to 1500 calories, which is a pretty big difference, if you care about how many calories you are burning.

You can also use an online calculator to figure out your calorie burn. If plug my numbers on this, I get the following values in cal/hour:

Now, that’s a purely flat ride. And there are obviously some aero calculations in there that may not be particularly accurate.

Another option is to use a heart rate monitor. My polar 720i claims to be able to compute the calorie burn for a ride. It knows my weight, my age, and my base HR. It also knows my altitude and speed, which could be very useful to compute calories, but AFAICT, it doesn’t use that in the calorie calculations.

On a recent ride, it claimed that I burnt 1110 calories in a 26.2 mile ride with 1445 feet of climbing, which comes out to around 42 cal/mile. How does that compare with the calculator above? Well, 1445 over 26.2 miles averages 1% over the whole climb – plug that in, and it gives an estimate of 1104 calories.

Which is really quite a bit closer than I expected.

When I was suffering up the climb to Sunrise on Ramrod, I was wondering how many calories I was burning. Given that it’s a climb and the speeds are slow, the amount of energy expended on climbing vs the energy expended overcoming air resistance is pretty high.

Here’s what the Polar says about that climb:

Duration: 95:30
Distance: 13.4 miles
Elevation Gain: 2820 ft (really 3000 feet, but the polar was low on the altitude of the top).
Calories: 1146 (85 cal/mile)
Speed: 8.4 MPH

The speed calculator suggests only 905 calories, for a paltry 68 cal/mile.

My bicycle climbs wattage calculator figures the following:

Wattage(Climb): 134 watts
Wattage(Rolling): 10 watts
Wattage(Aero Drag): 14 watts
Wattage(Total): 160 watts

Now, 160 watts is 138 Kcal/hour. But humans are only about 25% efficient at converting food calories into work, so that means the food calorie expenditure is 552 Kcal/hour, and the overall expenditure = 95.5/60 * 552 = 878 calories total (66 cal/mile).

Interestingly, that’s very close to the online calculator.

So, at least for that climb, if I’m of normal efficiency, the polar calorie estimation is perhaps 50% high. If I was dehydrated (and I was, a bit), that would tend to push the HR higher than normal.

Now, of course, the real way to figure out calories burned is with a power meter, but I haven’t taken that step. yet.

Another climb showed up with Polar=603 calories (97 cal/mile), calculator=465 cal (75 cal/mile), website = 446 cal (71 cal/mile).

What does that all mean? Well, it means that cal/mile calculations aren’t really worth much – which really isn’t a surprise to me. It also means that the online calculator does a pretty good decent job on pure climbs.

It also means that the polar seemed to drastically overestimate calories on pure climbs, but it seemed to be okay on normal rides.