Concept2 Forum

I have a Polar H10 Heart strap and use the Polar Flow App. Of course, the PM5/Ergdata also picks up my heart sensor. In a 30 minute row, the calculated calories burned are always less on the Polar Flow app than on the PM5/ErgData by about 40-50 calories. I understand that we're not talking about absolute measurements here, but I was just curious as to which is more accurate. If I'm recording or tracking calories I usually go with the Polar data, thinking the technology might be more "tuned" to heart rate and corresponding calories burned. (I also go with it since it's the lower calorie count and I'd rather underestimate the number of calories I've burned than overestimate). Then again, the PM5 might be more accurate as it takes into account the actual rowing activity.

Both the PM5 and the Polar Flow app are detecting the same sensor matching heart rates.

This might be just nit-picky and I don't really have a hill to die on here. I was just curious if anyone else out there had this on their mind.

David Hughes
Recent 5 Million Meter Club Member

I wouldn't trust either personally beyond - "if i sit here longer I burn more fuel than when i sit here a short time" or "If I go the same distance faster/slower it will make a difference to the fuel I burn doing so."

the Pm5 makes some pretty big assumptions about weight & also includes the "just living" expense in it's calcs - the polar probably only tries to factor in the extra from the exercise itself would be my guess as to the difference in the two though.

Ignore the PM5 calories unless you weigh exactly 75kg and use 300kcal just sitting on the ergo and believe the PM5 is correct. It's always been a load of nonsense just to get a reasonable number on the display.

Get your PM5 to show you watts or pace never calories.

doulos0 wrote: ↑

February 7th, 2025, 2:20 pm

the calculated calories burned are always less on the Polar Flow app than on the PM5/ErgData

Congrats on 5m meters !

Watts by convention are the power seen on the exercise machine. They are measured.

There is a numerical conversion of watts to Calories (C = P * t * 0.239005736) but if you use this you'll see this number is 5 times lower than exercise machine reported Calories.

Reported Calories on exercise equipment by convention are the energy your body consumed to generate the watts-hours, not the Calories delivered at the equipment. Included are estimates of your body's base metabolism, your body's efficiency, your weight, etc. Given rowing is roughly 20-25% efficient, there is a ton of slop in the Calories estimate. Different companies use different formulae. But there can't be a correct formula given a novice rower whose technique is poor and whose body has not yet optimized for rowing is burning a lot more calories than an expert rower at the same measured wattage.

Aside: C2 has a weight based calories adjustment you can use. Their calculator is here https://www.concept2.com/training/calor ... orm=MG0AV3

Concept2 Calories are roughly = 300 + 3.46 X (watt-hours)

My old Lifecycle bike uses roughly the following to get Calories from measured watts: Cal = 90.91 + 3.61 * Watt-hour. Close but not the same as the C2 formula.

Polar has to use different data to estimate calories because it doesn't see watts. Polar uses this --> "The Smart Calories algorithm has been developed using data from studies where wrist-based acceleration, heart rate and reference value for energy expenditure were measured." and "energy expenditure calculation is based on your measured heart rate and activity through wrist movement, and your personal information: weight, height, age, gender, your individual resting heart rate, maximum heart rate, and your individual maximal oxygen uptake (VO2max)." The polar algorithm is discussed here: https://www.polar.com/us-en/smart-coach ... t-calories

If using C2 machines, the heat we generate, corresponding to power generated, is 4Ws. 1kWh = about 860kCal.

The factor 4 takes account of muscle efficiency and internal work.

There is also body mass movement on the erg that C2 says corresponds to 300kCal/h.

If you want to know the calories burned, I would keep a log of metres rowed, calories consumed and weight. I believe loss of 1lb is approx 3500 cals so 3500 * lbs lost + calories consumed = calories burned. Calories burned = constant ("k") * rowing metres + non-rowing calories. Estimate what you were using before (or compare the "rowing" calories from low activity to high activity with similar other activity) and you get the non-rowing calries / day and can calculate k. Will be far closer than any machine outside a lab will calculate!