Neither would be very accurate anyway. Your HR @ 160-170bpm for an hour would represent the kind of work your body can do in its current fitness shape. Compare the same HR to a beginning rider would show them to burn off fewer calories. Compare your numbers to Lance @ 160-170bpm would show he's burning off mroe calories. The only way to accurately determine calories-burnt is to actually measure it. Put a rider in an isothermic chamber and measure how much he heats up his surroundings...