On one long ride that lasted roughly 3.5 hours, where I averaged 17.1 miles per hour, totals fell out like this:
- MyFitnessPal gives me a calorie burn rate of 644 calories per hour for fast cycling (16-20 mph average). The program credited me with a calorie burn of 2,254 calories.
- Strava data for the same file credited me with 1,663 calories. Strava's site says that the calorie number is based on power output. The power meter is the best tool, assuming it is calibrated and accurate. Strava does an estimated power based on your body and bike weight data if you don't currently have a power meter.
- GarminConnect (again based on the powermeter) gave a calorie burn of 803 calories for the same ride – obviously a huge difference between the three systems.
Which of the calorie burn numbers was accurate?
Depending on the site or the equipment, such as the exercise bike or treadmill in the gym, calorie burn is estimated by one or more of the following factors: heart rate, age, gender, workout speed, elevation gain, weight and moving time. Some sites or devices use their own scaling factors in addition to the hard data.
If a system uses only heart rate or age, I believe most of the time calorie burn is overestimated. I base this belief on past experience tracking calories and comparing calories consumed with those burned.
If a system uses only power output or heart rate, I believe calorie burn is underestimated. This is most apparent in mountain biking. While my heart rate might not be high on some of the trail sections (I don't run a power meter on the mountain bike), I'm putting out a lot of work to maneuver tricky sections of the trail. That is, a good deal of strength is needed for downhill riding and this effort isn't always captured by heart rate. Short, high effort exertions on the trail don't drive high heart rates, but come at a high physical cost.
More: Workout Placement Can Improve Recovery
All systems are estimating calorie burn in one way or another. No system is 100 percent accurate. If you are basing your calorie budget off of one particular system and are not shedding excess pounds, more than likely you – or your exercise system – are overestimating how many calories you're burning in your workouts. Or, you could be overeating.
With some patience and data collection, you can get a pretty good idea of calories burned during exercise to determine a rough number of calories burned per hour for your rides. Additionally, you can do your own calibrations for easy rides or increase it for really tough rides.
The bottom line is that you shouldn't blindly believe that you burned 800 calories during an hour of indoor or outdoor cycling and then eat to match that number in celebration of your calorie-burn accomplishment.
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