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Calculating Calories Burned

Old 12-06-15, 12:15 PM
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Andrew539
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Calculating Calories Burned

I know this is probably a popular question but I am rather new to riding and want to make sure I am understanding everything.

So when I first bought my bike I purchase a cheap $40 computer to try out. When riding it shows me burning a fair amount of calories per mile. This computer calculates calories based on distance and speed.

Since winter is approaching I purchased an indoor trainer that came with a Powertap sensor. The sensor relays the information to my iPad. This does not give me the calories burned but rather the power exerted. I know this is a more accurate way to calculate calories burned but the number do not make sense when compared to the original computer.

When riding outdoors I was averaging 15 mph(mountain bike) and burning about 50 to 75 calories per mile. I just performed a 30 min workout on the indoor trainer and my power output was 118kj. Which if I did the calculation right, which I don't think I am, it was about 44 calories burned. Compared to the other computer this doesn't make sense to me. I keep reading that 1kj is roughly 1 cal. And that would make sense but the online calculators keeps saying I burned 44 cal.


If someone could please help me understand this I would greatly appreciate it.
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Old 12-06-15, 12:32 PM
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thin_concrete
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Why can't you move the speed/distance sensor to the rear wheel so you can continue getting this information?
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Old 12-06-15, 01:07 PM
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When I use online calorie calculators, they all estimate that I burn approximately 50-60 calories per mile at my pace (17mph). When I use my Garmin Edge without a HRM, it approximates roughly the same. When I use the HRM, the Garmin calculates about 25-35 calories per mile. Strava also calculates roughly the same.

Based on my effort and fatigue -- and comparing it to running, which Garmin & Strava both approximate 120-140 calories per mile -- I'm guessing Garmin w/HRM & Strava are closer to an accurate count than the online calculators.
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Old 12-06-15, 01:08 PM
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The online calculator could be wrong. Like a lot of tools on the Internet, it doesn't mean that it is accurate.
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Old 12-06-15, 01:16 PM
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Originally Posted by Andrew539 View Post
...... If someone could please help me understand this I would greatly appreciate it.
Every hobby has the potential to turn the hobbyist into a bean-counter.... and there isn't anything wrong with that. I am sure both calculations are about equality as accurate. As I doubt a trainer uses as much energy as actually riding a bike. I have two apps that give two different calorie results for cycling.... I always just pick the lower number.
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Old 12-06-15, 01:28 PM
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On many levels, it just does not matter much. That is, most folks counting calories (I have been doing it daily for 18 months), are doing it for weight loss or management. And, what matters is whether or not you are hitting your goals. When I was younger, I could out exercise virtually any calorie count of food. Nowadays, I need a lower calorie count of food and I cannot out exercise bad eating habits, especially given my knees....
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Old 12-06-15, 01:53 PM
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If you go by the math, 118kJ is 28Cal. The conversion is 0.24Cal/kJ. The kicker is that the human body is only about 25% efficient in converting Calories to useful work, so if your power meter says you exerted 118kJ, your body actually burned 4 times as much energy due to its inefficiency. So, the 28Cal suddenly becomes 28*4Cal=112Cal. This is where the approximation that 1kJ expended by your body is approximately 1Cal burned by your body.

If you have a power meter this is going to be the most accurate measurement of calories burned. If the power meter says you expended 118kJ, then you burned about 118 or so Calories. This is a close approximation and it depends on your own bodies' efficiency.
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Old 12-06-15, 02:00 PM
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That definitely help. I just wanted to make sure I was understanding what I was reading in different articles. I appreciate the help.
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Old 12-06-15, 04:32 PM
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Originally Posted by CeeDotA View Post
When I use online calorie calculators, they all estimate that I burn approximately 50-60 calories per mile at my pace (17mph). When I use my Garmin Edge without a HRM, it approximates roughly the same. When I use the HRM, the Garmin calculates about 25-35 calories per mile. Strava also calculates roughly the same.
Garmin is pretty good with the HRM. Most people seem to think 30 calories/mile is realistic
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Old 12-06-15, 04:59 PM
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Most calorie counters overestimate calories burned.

I have found that the following is a much more accurate assumption for me:

100 calories for every 5 kilometres cycled outside.


Therefore, at 20 km/h, I would burn 400 calories/hour. If I happened to pick up speed, I'd burn more in an hour.

Being that riding a trainer is easier than riding outside (although it may not seem that way because of the boredom factor), I estimate about 350 cal/hour when I ride the trainer.


If you do a bit of a search, you'll discover that 40 calories/mile is a common calculation, although more recently there is some thought that 40 calories/mile is a bit high, and that 30 calories/mile is probably closer to accurate.

40 calories/mile works out to about 25 calories per kilometre or 125 calories for every 5 kilometres cycled.
30 calories/mile works out to about 18.75 calories per kilometre or about 94 calories for every 5 kilometres cycled.

So my assumptions are right in that ballpark ... and because one of the reasons I cycle is to lose weight, or these days, maintain my weight, I'd rather estimate calories burned on the low side.

Last edited by Machka; 12-06-15 at 05:03 PM.
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Old 12-07-15, 10:53 AM
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Seattle Forrest
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Originally Posted by Andrew539 View Post
I know this is probably a popular question but I am rather new to riding and want to make sure I am understanding everything.

So when I first bought my bike I purchase a cheap $40 computer to try out. When riding it shows me burning a fair amount of calories per mile. This computer calculates calories based on distance and speed.

Since winter is approaching I purchased an indoor trainer that came with a Powertap sensor. The sensor relays the information to my iPad. This does not give me the calories burned but rather the power exerted. I know this is a more accurate way to calculate calories burned but the number do not make sense when compared to the original computer.

When riding outdoors I was averaging 15 mph(mountain bike) and burning about 50 to 75 calories per mile. I just performed a 30 min workout on the indoor trainer and my power output was 118kj. Which if I did the calculation right, which I don't think I am, it was about 44 calories burned. Compared to the other computer this doesn't make sense to me. I keep reading that 1kj is roughly 1 cal. And that would make sense but the online calculators keeps saying I burned 44 cal.


If someone could please help me understand this I would greatly appreciate it.
Then you burned approximately 118 kCal.
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Old 12-07-15, 11:08 AM
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andr0id
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Originally Posted by hayden52 View Post
If you go by the math, 118kJ is 28Cal. The conversion is 0.24Cal/kJ. The kicker is that the human body is only about 25% efficient in converting Calories to useful work, so if your power meter says you exerted 118kJ, your body actually burned 4 times as much energy due to its inefficiency. So, the 28Cal suddenly becomes 28*4Cal=112Cal. This is where the approximation that 1kJ expended by your body is approximately 1Cal burned by your body.

If you have a power meter this is going to be the most accurate measurement of calories burned. If the power meter says you expended 118kJ, then you burned about 118 or so Calories. This is a close approximation and it depends on your own bodies' efficiency.
A power meter that uses some type of strain gauge such as a PowerTap hubs, Vector Pedals or Stages crank set are going to give you fairly accurate information. They are not laboratory instruments so they will not be perfect.

I have a PowerTap hub and my experience is that most of the computers that guess your calories based on heart rate, age and weight overestimate a lot.

Example, I have a 4 mile circuit I ride on a regular basis and depending on wind, I do that route in between 12:30 and 13:30 minutes and the kj per lap is between 150 and 160. 4 laps is always about 600 kj +/- 20 kj and has been for a year.

I used a different rear wheel without the PT and road the same 4 laps at 13:00 average and my Garmin told me it was 1100 Calories. There is no way that could be correct.

It's going to depend some on your age and fitness, but if a guess type calories calculator tells you you're burning more that 600-700 calories/hour, it is likely lying. Well, you could be cycling up Mt. Everest or beating Lance Armstrong on a time trial, in which case, maybe it's telling the truth.

Originally Posted by Machka View Post
If you do a bit of a search, you'll discover that 40 calories/mile is a common calculation, although more recently there is some thought that 40 calories/mile is a bit high, and that 30 calories/mile is probably closer to accurate.
An out and back ride for 20 miles at 19/20mph will set me back about 600-650ish calories, so that is in line with your values. Road bike, riding hoods, moderate wind and hills.

Last edited by andr0id; 12-07-15 at 11:13 AM.
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Old 12-07-15, 01:49 PM
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FWIW, the stationary bike at the gym registers about 36 cal/mile at load #11 out of 25. My cadence is 105-110, but the calories appear to be distance, not speed, related.

My Cannondale CX on rollers at home seems a greater workout, based on heart rate and sweat production (even with a cooler room and closer fan than at the gym). Cadence at home is 90-100.
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