[reply]6000 kcal, would be an average power output of 256 W over 6.5 hours, which would mean either you're an elite level cyclist/triathlete with a mass of ~ 70 kg, you're considerably heavier, or you're S710 is way off.
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The Polar is measuring Calories burned by the body, not the power to the drivetrain or the ground (like a PowerTap, SRM, or even Polar power unit would.) If you assume that the rider is 50% efficient, he would be producing 128 W.

Ray