today i did a 3hour ride that was just over 60miles over a fairly hilly route. i wear my garmin 305 in my back pocket just to keep track of distance and a polar hr monitor to keep track of my HR. i try to use that to judge my output rather than mph with the garmin(if its in my pocket and i cant pay attention to the mph i ride much more smooth) when i got done with the ride the garmin(on bike setting) said i burned over 5500 calories while my polar watch said about 2800. pretty big difference, is one more accurate than the other? they are both set to my age weight sex and height.
maybe someone that knows a bit more about this can chime in, i have no idea how much power levels go up as body mass goes up, which would deff effect cal burned.
Something in the settings of the Garmin is off. It might be in “run” setting which would line up roughly with 60 miles run (~90 cals/mile which is a bit low, but more in line than what that distance would be cycling).
The polar is off as well, but but will always be off because it’s doing ballpark estimates based on averages of populations rather than off what you yourself do.
3 hour ride @ ~200 watts will burn roughly 2100 calories, which also makes an assumption for efficiency. I don’t know if this is the wattage you rode at, but that might give you an idea of ranges.
The Polar sounds much more in the ballpark (if you could burn 5.5kkal in three hours of training you should tell Alberto you’re taking his jersey next year). What may be screwing the Garmin up are the downhills. Garmin’s have never been that good at determining grade%…and the computer probably thinks that you’re working pretty hard to go 30-40mph when it’s reading 0% grade.
A power meter would be much more accurate, but even those have to make a guestimate for your metabolic efficiency (usually 22-25%).
My Forerunner 305 was never right. I wish it was but it’s not even been close. The best part is that it calculates calories burned and you don’t even have to wear a heart rate monitor.
I’ve noticed the same thing with my Garmin. I even input my weight (145), age (23), cycling mode…all that. I rode 120 miles (~6 hours) and it told me I burned about 8000 calories. I sure hope it’s wrong!! However, I probably ate that much in PB and Nutella afterwards so maybe I should hope it’s right.
Is calorie burn independent of heart rate, and only determined by power output? As I get fitter, I can ride faster at a lower heart rate, so my Polar (HR only) says I’m burning fewer calories. But, I assume that if I had a power meter, it would be saying I’m putting out more power.
So am I burning more calories because I’m making more power or fewer because my heart rate is lower?
2800 is a lot closer. That would be 933kcal/hr, or roughly 220W (which would be in the right range for 20mph).
The Garmin implies that you were pushing over 400W, which at 20mph translates to the world’s worst aero position ;P.
Note: If you are in my AG (40-44) then the Garmin number is absolutely correct and you need to start eating that many additional calories to make sure you are fully refueled.
So am I burning more calories because I’m making more power or fewer because my heart rate is lower?
Are you doing more work going faster or less?
Can I go faster while doing less work assuming all other variables (same bike, same wind, etc) stay constant? I don’t have a power meter, but I can tell you that a 40 mile ride I used to average 20mph for with an average heart rate of 150, I can now do at the same speed with an average heart rate of 135. Does this not indicate an increase in power output?
Is calorie burn independent of heart rate, and only determined by power output? As I get fitter, I can ride faster at a lower heart rate, so my Polar (HR only) says I’m burning fewer calories. But, I assume that if I had a power meter, it would be saying I’m putting out more power.
So am I burning more calories because I’m making more power or fewer because my heart rate is lower?
For aerobic level riding there is a pretty linear relationship between mechanical work done (average power x duration) and total energy metabolised*.
Since the relationship between HR & power is somewhat variable, I’d suggest HR is a significantly less reliable an indicator of energy metabolised.
to an extent it depends on how much your gross metabolic efficiency may change during a ride (there are a few factors to consider, such as fuel substrate utilisation ratio, variability of effort/lots of neuromuscular power efforts, duration/fatigue, environmental/temperature and no doubt others). On the whole though, GME isn’t going to change much in a trained cyclist ride to ride or season to season.
It depends how much faster you are going. If you have lost weight, some portion of the speed increase could be due to reduced weight (rolling resistance) and body mass (frontal area/drag)
I would guess that as you have become fitter, you are able to do more work and that is the reason for the majority of your speed increase.
A power meter could tell you for sure. Some time at analytic cycling could provide an increased degree of confidence compared to guessing.
You’ve discovered a known flaw in how HRMs calculate calorie expenditure.
having quit smoking almost 4 weeks ago, my heart rates have come down considerably at any given effort level. haven’t gained or lost weight, position on the bike hasn’t changed, but a 19mph ride used to be ~150bpm and is now ~130bpm. HRM says i’m burning fewer calories, but i’m doing exactly the same amount of work, so wouldn’t calorie expenditure be the same since the actual wattage required to complete X distance with Y elevation change at Z speed (with all bike/rider factors constant) is the same?
