I'm a bit perplexed and before I abandon all trust in my HRM I'm hoping someone can give me a reasonable explanation for this.

I have a Garmin FR60 with heart rate monitor and bike sensor kit. I'm riding on a MAG trainer in my kitchen.

On Sunday I cycled 42:50 minutes, a distance of 18km, average speed of 25kmh and an average heart rate of 117. Average Cadence of 74, max of 107. My Garmin worked that out to be 784 calories.

On Wednesday I turned up the resistance a bit, I did 48:09 minutes, a distance of 11.5km, average speed of 14.4kmh and an average heart rate of 137. Average cadence 74, max of 118. It felt like harder work with a few more sprints but the Calories for this was 342.

I looked into how Garmin works and apparently for the FR60 with Heart Rate strap it's a simple heart rate/age/weight calculation.

Any ideas for the discrepancy in calories burnt?

HR doesn't equate to Calories.

Did the age or weight values get changed?

I thought the harder you worked the higher your heart rate. The higher your HR the more calories burned. At least given we are talking about the same person, weight, age, etc. Not true? Then what does equate? I'm confused.

It sounds like your Garmin is calculating your calories based on distance and time rather than HR. Could that be true? Maybe there's a setting where you tell it to use HR vs. distance - time calculations?

Can you also choose an activity on your watch? Was it maybe set to cycling on one day and running on another?

The first number of 784 is by the way totally wrong for sure. It would amount to a biker in the low to mid racing categories going all out for 43 minutes.

The second number sounds much more reasonable.

Go ahead and abandon all trust in the calories your HRM shows, because it's next to useless.

Further investigation. I've done 3 rides this week:
48mins 11.5km avg HR: 137 Calories: 342
42mins 18km avg HR: 117 Calories: 784
40mins 12.5km avg HT: 130 Calories: 447

The watch has stayed the same, all are logged by Garmin as "cycling" - I didn't touch it in between times.

According to calculators off the internet:
Based on hr/time/weight/age the calories for these 3 rides should be : 703, 489, 543
Based on time/speed/weight/age the calories should be: 428, 771, 440

So it does look like the calorie estimate is coming from the time and distance rather than the Heart Rate.

What's the point of the HRM then if it doesn't even use it!

mr_pedro - I'm no racer, I'm at the other end of the scale 240lbs and pretty out of shape.

How would Garmin know about your "speed" when it is a GPS and it clearly sees that you're stuck in one point (on top of your trainer in your kitchen)?

It's got a sensor on the back wheel that measures distance - it also measures cadence with a sensor on the pedal arm - it's all very clever - except it's clearly rubbish at working out calories based on heart rate which I would have thought would be more accurate - what if I'm coasting down hill it's going to think I'm burning millions of calories.

Took a look at the manual for FR60. First of all, I was wrong, it is not a GPS, it's just a heart rate monitor / sensor receiver watch. It also says that it calculates calories based on HR if it does not detect a speed sensor.

Using HR is not a sure solution. Two different people with different fitness levels would burn different amounts of calories at the same HR. It might make more sense for the watch to assume that you're outside riding on a flat road if it receives data from a speed sensor. This way it will calculate calorie burn based on what it thinks it would cost you to push through the air at that speed.

That said, it does not seem to be doing a very good job at THAT, either, since there's no justifiable way for it to report the burn of 1100 calories/hour riding at 25 kmh. Whatever other assumptions it makes, it should be reporting something in 500..700 cal/hr range at that speed and your weight.

I would suggest to turn off the speed/cadence sensor if you want to keep getting calorie counts. I can't guarantee that numbers it reports will be any closer to reality.

I already expected you were no racer , that is why burning 1000+ cal/hr is a very big overestimation.
Without being to scientific about it I expect you to be able to do between 350 and 550 cal/hr at a pace that makes you sweat and breathe hard.

There are a couple of things wrong with your calculations. Lets concentrate on 1 figure, eg:



The average speed was 25.7 km/h, on a flat with no wind this requires 130W and for 42 minutes that gives you something like 315 Cal, not 771. So I don't know what you are using to calculate calories based on speed on the bike, but it seems wrong.
Another problem is that doing 25.7 km/h on the trainer might not be the same effort as doing it on the road, which is what the calculators are assuming, but it could be that your trainer has been calibrated to give a realistic resistance based on speed.

I guess this is the key - estimating calories using the sensor is fairly pointless because my trainer is nothing like being on the road.


I just used a couple of generic calorie calculators off the internet - I tried a few they all seem to use the same formula as they came out the same.

+1

You'd be better off just assuming you burn 500-600 calories per hour.

Endomondo says I burn around 600-700 calories for a 30km/1hr ride (manual entry) For a real on the road gps tracked ride at 28kmh average it comes out at around 700-800 calories. . My exercise bike says I burn around 500 calories for the same time/distance. They are estimates but I take 400-500 calories an hour as a good guess.

Quit trying to get around it - it doesn't work. Two riders - same age, fitness, etc. - can have a 30 bpm difference. The HR of the same rider changes depending on humidity, hydration, time of the ride, amount of riding in the last week, amount of sleep, stress level at home or work, and on and on. HR cannot give you Calories.

I'm surprised some legal shark hasn't picked up on this for a class action suit - millions of Garmin buyers have been lied to. Should be some big money in it.

If you weigh about 240 you're about the same as me.

I reckon that road cycling burns something in the region of 40 calories per mile, maybe increasing that to more like 50 if I'm pushing hard. The extra calories there represent the extra work to maintain a higher speed or go up bigger hills. I use the figures purely as a guideline if I'm thinking of what, if any, food I might need to take with me. As a rule of thumb I reckon I should be able to ride about 50-60 miles without taking on any food at all but will be hungry at the end of it.

If you're on a trainer then I'd round down a little as you're not dealing with any wind resistance. Since I like nice round numbers so I can multiply in my head I'd guesstimate a figure more like 30 calories per mile and not increasing it as you go faster as you don't increase wind resistance.

Doesn't even need to be two different riders. I reckon my HR jumped by 20-30bpm when I got buzzed by a jackass driving a truck with a dumpster on the back of it, despite my effort going right down as I got out of its way.

here is a nice read about the different ways in which Garmin devices calculate calories: https://www.dcrainmaker.com/2010/11/h...on-garmin.html

Agreed. I am sure my polar is a liar. I'm going with this.

^^^+2. I've used a HR calorie formula I tweaked for me based on a week of riding with a power meter. Although it's reasonably accurate and my calorie burn varoes up a down a bit, using an avg of 600 cal/hr is close enough for practical purposes. I typically average 80% of my max HR on my rides.

I have a puzzle of my own.

I wonder why Garmin and Strava disagree about my calories burned even with a power meter?

For the last 3 activities, Garmin Connect reports 994, 583, and 1654 calories. This is consistent with what was shown on the screen of the unit at the end of the ride.

For the same 3 activities, Strava reports 1279, 655 and 2136 calories. There's no apparent pattern.

* Activity 1: Garmin: 994, Strava: 1279, weighted avg power: 122 W, moving time: 3:07, avg speed: 12.1 mph
* Activity 2: Garmin: 583, Strava: 655, weighted avg power: 158 W, moving time: 1:15, avg speed: 13.7 mph
* Activity 3: Garmin: 1654, Strava: 2136, weighted avg power: 168 W, moving time: 3:29, avg speed: 15.4 mph

Trust the Strava data. For calculating caloric expenditure you should be looking at total work measured in kJ and multiplying by 1.0 or 1.1 to get calories. Weighted avg power is NP and not useful in calculating calories. I believe Strava uses a factor of 1.12 to go from kJ to calories.

Garmin connect doesn't calculate avg power properly and reports moving avg power excluding zeros which happen when coasting. Their total work seems to be accurate so you could just look at the work in kJ and use that number as calories. I don't know how they come up with the calorie number on their site (probably HR based) but it's not correct.

The site reports the same number that was displayed by the unit. I don't think it's HR based: it does not increase when coasting. Next time I'm riding, I'll note the kJ figure and compare it with all the others.

It looks like it will try to use HR if available. Try a ride without your HR and it will likely be more accurate. From Garmin's support site:


https://support.garmin.com/support/s...00000000000%7D

Some math:

.0539 Cal/watt/min + 1.23 Cal/min is the calorie burn formula used by a popular exercise equip manufacturer. The first part converts your measured power output to Cal (or Kcal). The second part is how much you burn (an average) just sitting on the bike being alive.

An ESTIMATE of the power needed for an average cyclist to be effective at riding outdoors and climbing hills is 1 watt per lb of rider/bike weight. So a 175 lb bike/rider would need to produce an average of 175 watts while riding.

Lets assume a 45 min ride:

.0539* 175 * 45 + 1.23 * 45 = 479 Cal

This is based on MEASURED watts. To make this kind of calculation based on HR is marketing.
Two people, one fit, one not. Will their HRs be the same for the same amount or power output? No.
Two people, both fit, same age, same size. Will their HR be the same for the same power output? No.
Two people, same HR, same measured power output. Both same fitness level? No. One could be trained athlete, other could be a beginner about to stroke out.
Same person, different days- will their HR be the same for the same power output? No. It can vary based on sleep, training load the days before, stress, etc.
And in all of these cases, calorie burn is based on power output.

Pick up a good book on HR zone training, and use your HR monitor to help you determine your training zones and improve fitness, and forget about watts and calories unless you have a power meter (and race, IMHO).

And no idea why your Garmin would show such a high number for that one session...

Pulled most of this from an indoor training instructor forum.