I've read somewhere online that Polar claims their HRMs to be +/-15% accurate on calories burned when compared to controlled laboratory measurement.

I wanted to compare mine with what I get off my Road Machine since the power/speed curve is supposedly pretty well defined and I can back-calculate calories from that.

After riding yesterday, I jumped on the trainer for 40 minutes. The HRM (Polar CS300) says I burned 612 kcal in that time, but the results from converting my average speed (14.4 mph) to calories via the Road Machine power curve (P=5.24482*S+0.01968*S^3, P=134.3 W for 40 min) gives me about 77 kcal*, which doesn't make any sense**. Am I using the wrong conversion from watts to kcal? I'm using 1W-h = 0.86 kcal.

Anyone try anything similar? Is there any way to get a reasonably accurate ballpark of energy expenditure w/out a power meter?

Thanks.



*Assuming about 25% efficiency between body/bike/trainer, that's up to 308 kcal.
**Neither does the 2000 kcal spent over 2 hours and 20 minutes which gives me a sustained power output of 246 watts. That's not right. I'm pretty slow and wimpy.