Concept2 Forum

I own a Polar F6 Heart Rate Monitor.

I have put in all my data as far as age, weight etc. It does have a calories burned display, which I am sure it calculates off of my heart rate. I notice when I really increase my intensity that my calories burned shoots up much more than compared with what the display shows on my Model C ergo meter.

Which should I believe?

I would not trust the polar. It is a whole lot better than nothing but it is only a rough indication.
The C2 will be pretty consistent, since it is based on how much work you do but it necessarily has some built in errors that will differ for each person. Your heart rate is not a reliable indicator of how many calories are burned.
Your heart rate is only an approximation to how much work you are doing, while the C2 measures the work directly. Your heart rate will change for the same amount of work as your conditioning changes. The errors in C2 calorie measurements will only change due to changes in efficiency which could be by better technique and also by metabolic improvements which happen very slowly (and I think mostly by endurance training).

Having said all that. I would worry about conditioning and getting faster and in better shape and ignore the calories.

This is from the manual for the PM2:

A Word About Calories:
Due to the differences in body weight and efficiency, calories on the PM2 are only an approximation of calories burned by the person rowing. The formula used in the PM2 is as follows:

Calories = (4x ave watts/1.639)+ 300 cal/hour x time rowed (in hours)

This formula assumes a person of 175 pounds (80 kg.) and a base rate of 300 cal/hour to move your body through the rowing motion at 30 strokes/minute.

If not this formula in the PM2+, PM3 & PM4, it would need to be another like it. Unless those assumptions are correct for you, the result will also be incorrect. If you are simply using the "calories" measure to see whether you've done more or less work than last time, it should be fine. If you're trying to match calories expened on the erg vs. calories consumed I would be extremely cautious!

HTH,

Alissa

Calories = (4x ave watts/1.639)+ 300 cal/hour x time rowed (in hours)

should of course be

Calories = (4x ave watts/1.639 + 300 cal/hour) x time rowed (in hours)

This is a strange formula. I am not impressed. They may have measured this for someone and this is an empirical curve fit. It may be an indication thatC2 doesn't take Calories burned very seriously. So you shouldn't either.

The formula implies that when rowing at a 2:00 pace 38% of the calories goes into moving your body back and forth. At a 1:45 it would be 29% of the calories. Not very likely. The formula is probably only correct for a limited range of speeds for a limited range of body types.

From first principles the formula should be a
Calories = (1/efficiency)* * ave watts / 1.163 * time.

(there are 4186.8/3600= 1.163 watt-hours per Calorie

The term for efficiency has two parts:
1) the biomechanical/biochemical efficiency from converting food into work and from friction losses in the joints. For cyclists it is usually 20-22%. Probably is similar for rowing. The formula above implies it is 35%, which way too high.
2) the mechanical efficiency of the movement (wasted energy moving the body) and of the machine losses. (chain, bearing, and slide friction).

Since they wanted to seperate out the movement of the body (which is intellegent), they could have varried it with stroke rating and let you input your height and body weight.

Someone pointed out in a cycling/rowing thread recently that a study concluded that the Erg reads about 25W less then power measured using strain gauges on handle, and that it reads low when changing speed.

All of this is to say that don't take any absolute numbers too seriously. All that is really important is that the machines are consistent.

Even with the imperfections in this formula, for most people it is probably better then those based on heart rate.