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.
