marzjennings said:
If you've changed none of the bike's settings how is the power output the same whether you cycling at 90rpm or 70rpm? Sounds like the wattage calculation done by the bike is dodgy.
But you're right that cadence is directly related to HR. Cycling at 20mph on the flat at 110rpm (low gear) is going to produce a higher HR than 20mph at 80rpm (high gear). And yes, pure heartrate is a poor reference to calculate an accurate kCals/min as there's little or no indication of effort (watts).
A gym bike is just the same as a Cyclops Powerbeam Pro trainer.
It has a load cell which senses Torque and a rev counter that counts the revs.
kW = ( Torque [Nm] x rpm ) / 9549.3
Cadence is NOT directly related to HR. HR is a consequence of moving your legs more times per unit time.
When we say 'directly related', it means there is a solid, undisputed correlation factor to convert from one unit to the other.
eg. kCals/min = kW x 14.3197
If my HR is 160 and my cadence is 80, the correlation factor would be HR = cadence x 2.0000
When my cadence is 90, is my HR 180? No. it's not related.
Nor is HR and kCals/min.
As seen by my own eyes, when the absorption of the gym bike was 225, my HR was 153 OR 144, dependent on cadence ( the number of times my legs are moving up and down ).
I have mentioned on this chatboard before about performing a 'Natural cadence' test.
It involves setting the gym bike to a nominal absorption and then pedalling, increasing the cadence very slowly through a wide rev range.
When your HR is lowest, that is your 'Natural cadence' and the revs which make your heart beat less for the power output. Well, to be truthful, it's the rate of effort that your muscle fibre Fast/Slow twitch balance is most comfortable with.
Believe it or not, mine is 45 rpm. That is why I'm able to climb a 20% hill on a 32" gear at 3 mph at 33 rpm.