Calorie Burn Accuracy

First time using the F7XSS paired to the rowing machine on Wednesday.  Obeservation:

Garmin calculated 943 calories burned, compared to Concept2 PM5 calculated 1807.  Note that I was wearing my Garmin HR strap (which I do for all rowing sessions, weight training, and HIIT workouts) and was paired to both the FENIX7 and the Concept2 ERG.  Average heart rate was within 3bpm between Garmin and Concept2 for the duration of the row, yet Garmin FENIX 7 estimates half the calories burned.

All other metrics collected by the FENIX7 were accurate, to include stroke rate, distance covered, 500m split pace, and power.  Attached image is the same rowing session from each data source (Garmin FENIX7 on left | Concept2 PM5 on right).

Anyone else noticing this with fitness equipment paired directly to the watch?

  • I've noticed that the calories burned on the indoor row activity on the Garmin 7x are low compared to what they should be. I'm not doing 30km in a session (thats impressive!) and don't have the PM5 but I did a 5k row yesterday and it only recorded it at 258 calories doing a 2:03 / 500m pace

  • 5K @ 2:03 is definitely more than 258cals.  Are you using a heart rate strap while rowing, or just the wrist-based OHR on the F7?

  • Just the HR monitor on the watch itself. 

  • With 152w average power (and at low, 120 bpm hr) the ~950-1000 calorie / 2 hours would be roughly correct if it were a bike ride. To burn 900-1000 kcal / hour almost all in efforts needed and that would cause a hr around the lactate threshold. 

  • Except that this activity is a row, not a bike ride.  Also, I'm using the Garmin HR chest strap, so you are suggesting that the HR data being received by the Concept2 rower is being incorrectly increased?  All of my rowing sessions using the same HR strap and rower average ~900 calories per hour over the last 5 years.

  • I row and ride too. On the bike calories are measured from the power if powermeter is attached. On the erg, pm5 watt data is not used by Garmin. Calories calculated from hr only. But believe me, with 120 avg hr you can't burn 900 kcal/hour (except if your max hr is 125). 

  • I'm not sure what you mean by watt data not being used by Garmin.  It's clearly listed in the metrics for each rowing activity with values for Average, Max, and Normalized.  I find it very hard to believe that only 943 calories were burned in 2+ hours of rowing, especially given that the recorded HR on both the PM5 and the Fenix7 were between 120-132bpm for the last hour.

  • I think so as well. We're so used to inflated calorie burn numbers that we forget to think of what these numbers actually mean. 900 calories per hour is massive and not something that the average non-professional sporter churns out regularly, and certainly not with such low HR. But there's a way to test it.
    Use a good TDEE calculator, like this one here: exclude the workout calories (thus only BMR), do this a few times per week, track all calories you eat with a food scale in grams, and eat back all calories that the concept gives you for a month. With a difference of 900 calories per workout, 3x per week over a month you might potentially gain 3lbs. Or not. Then you might have an idea which one is more correct (assuming water weight fluctuations are not too big)

  • I mean that this data in a rowing activity is not used by Garmin for calculating the calories. Garmin estimates it from your HR and the HRV. In stead of this the Concept PM5 estimates the burned calories from the measured power and this is usually way overestimated. Enough to tell 2 numbers: 900 kcal/hour @ 120 avg heart rate. If you know the ususal efforts/power numbers you can/should easily tell that it is too high/not possible. If it were 250 Watt for 1 hour @ 170 BPM hr, 900-1000 kcal/h would be realistic. But it is just my opinion. You can calculate with that number which you want.

  • I'm a bodybuilder and also doing vigorous bikerides a few times a week. At my peak form with 300W FTP, at my lactic threshold hr (167) I can burn 1100 kcal. I don't tell /hour because I am not able for that pace for more than 1 hour. And I am at athlete level with 58-60 VO2max with more than the average muscle mass.