I agree that the spin scan is an excellent tool and we utilise it during the fit to explain the best efficiency to achieve in pedal style.
As Computrainer explain it its not a “magic bullet” http://www.computrainer.com/rm1/Online_Help/SpinScan.htm
*SpinScan offers efficiency improvements a few ways. *
The SpinScan number (SS) - showing torque efficiency as defined above. Ranges from low 30’s to high 80’s (typical). There is no ideal number, but the goal is to make this number grow, over time, while maintaining the same wattage/RPM/Speed relationships.
In their process they also talk of holding all other factors constant when using one parameter as a reference. So as Travis R suggested "Inversely, if the power was the same, but the heart rate lower, wouldn’t that also be more efficient? In your example where you drop the seat too low, wouldn’t the heart rate go up? " this would be correct.
A more inefficient position would create a higher heart rate.
I was looking for a measurable variable that we could utilise fairly fast and accurately. The only real test is to do a 8 min max power output test, but the parameters are too hard to keep constant. Likewise Heart rate needs some time to “kick in” and show effects as there is a bit of a lag and so is less “instant” like we are achieving with power.
We could use any of the parameters as a verification tool of efficiency, cadence, Heart rate, spin scan or power.
The two thoughts are that.
1: All other variables have to be kept near constant in order to get efficient reading of the measuring variable ( be it cadence / HR / Power or spin). So if you are using HR as the measure of efficiency then power, cadence and gradient need to remain constant. Like wise if cadence is the measured variable then power / HR and gradient need to remain constant.
2: The assumption of- with greater efficiency in fit required power will go down (or HR down or cadence up) is the bigger question.
Assumption 1 is basic science, so that’s already been verified by much smarter people for many years.
For 2 the assumption comes from we are measuring “power” in a fit situation as pressure on the pedals, that is how much force is required to shift the cranks round at 100 rpm.
We are actually measuring how efficiently they can achieve 100rpm (or 60rpm / 80rpm or any number).
If we look at a crank and bearing interface as an analogy
Loose ball bearings with oil - spin with a fingertip pressure - less force required.
Seized cartridge bearings with lots of rubber seals - lots of force required to spin.
So less force required to achieve a given output should be a sign of greater efficiency.
It may be that using the GURU DFU system is allowing us to better track power as a measurement, we never did before as people had to get on and of the bike so measuring would been interrupted and not consistent. I do not think the numbers are accurate enough to be the holy grail of fit or to be the only tool of reference or verification.
If we do not follow F.I.S.T protocol or try to use power only or cadence only, the positions achieved come up weird. It still requires a fitters skill.
But as a verification tool of “this is the best fit for you (the customer) because…” it is proving to be excellent.
Thoughts and critique appreciated.
Hugh