RPE of L2

[gudujarlson]

I have observed a gradual increase in RPE during L2 rides along with an increase in power. Back in April I did my L2 rides at about 150 watts based on my measured FTP of 220 watts. These rides felt extremely easy and it required concentration to keep the watts down. My heart rate hovered around 85-90% of LTHR. As the season progressed, my FTP rose to 244 watts and now I ride my L2 rides at 180 watts. Now I have to concentrate to keep the watts up even though my heart rate is lower: 80-85% LTHR. My fitness has obviously risen, but it feels just as hard to peddle at a given wattage. I kind of expected my RPE to intensity ratio to remain the same as my fitness increased, but that does not seem to be the case. Perhaps the keys are: a) RPE is more than perceived peddle force; it also includes breathing rate, muscle burn, etc. and b) I tend to pace myself using peddle force only. Has anyone else experienced this?

This got me thinking. Some pros have FTPs of 400 watts. What does it feels like for someone with a FTP of 400 watts to pedal at 400 watts for 20+ minutes. For me 400 watts feels like I am pushing really hard on the pedals. I can't imagine pedaling that hard for an hour. I'd expect my joints to fall apart or something.

 

[daveryanwyoming]

Originally Posted by gudujarlson ....This got me thinking. Some pros have FTPs of 400 watts. What does it feels like for someone with a FTP of 400 watts to pedal at 400 watts for 20+ minutes. For me 400 watts feels like I am pushing really hard on the pedals. I can't imagine pedaling that hard for an hour. I'd expect my joints to fall apart or something.

Remember power is both pedal torque and cadence (actually angular velocity, but that's directly related to cadence), not just the torque part. You can sustain 400 watts at 80 rpm with roughly 63 pounds of average pedal force or you can sustain the same 400 watts with roughly 50 pounds of average effective pedal force by pedaling at 100 rpm (assuming 170mm cranks in both cases). IOW, pedal force is only part of the equation and relative to something like walking up a flight of stairs or hiking uphill with a pack on your back the average pedal forces aren't really very high (peak pedal forces are typically twice the average force per complete pedal cycle but still not huge compared to body weight).

Regardless I don't have an FTP of 400 watts but I strongly suspect the RPE for a rider doing 20 minute intervals at their FTP of 400 watts isn't very different than us mere mortals doing them at our lower FTPs. FWIW, when I first started training with power I suffered mightily to finish 20 minute efforts at 220 watts, Fast forward several years and my best 20 minute efforts have risen by over a hundred watts on my best days. But the RPE to pull out a 300+ watt 20 minute effort is no higher than the RPE was to do them in the 220 watt range six years ago and over the years the RPE to hold my FTP or a bit above my FTP for 20 minutes has always been about the same.

Your example of sub maximal efforts feeling harder now that your FTP has risen is interesting but again that doesn't really change how hard maximal efforts feel as your fitness changes. A full out 20 or 60 minute effort hurts a lot in the final minutes, hopefully the numbers increase as you train but the RPE really shouldn't change much after the initial period where you first learn just how hard you can work.

Perhaps as you say it's because you tend to associate pedal force with power instead of things like breathing (a much better proxy for effort) or overall RPE of everything and not just your legs. You might try a few long intervals at your typical working power but shifted down a couple of cogs and spinning faster to maintain the same power. I'm not suggesting, as some might, that this is a 'better' way to train but just a way to get your head around full system RPE and not just tuning into pedal force. Hold your same power at 100+ rpm for 20 minutes and I think you'll see quickly that it's not just pedal force that limits power production.

-Dave

 

[gudujarlson]

Ya, I think I confused things by using a threshold effort as an example. I don't notice any RPE difference during those efforts now compared to April. Those tend to be very intense focused efforts where my mind does not have a chance to forget how fast I am going. During L4/L5/L6 efforts, I guage my RPE more on the burning in my legs more than anything else. A better example would be a rider with a FTP of 400 watts riding at 280 watts for 3+ hours.

BTW, for a couple years now I tend to average 95 rpm on L2 rides and 100 rpm on more intense rides.

 

[qcwtom]

Dave, that's really interesting.

What is the formula for calculating force based on power and cadence?

 

[gudujarlson]

Originally Posted by qcwtom .

Dave, that's really interesting.

What is the formula for calculating force based on power and cadence?

http://home.trainingpeaks.com/articles/cycling/quadrant-analysis.aspx

 

[gudujarlson]

I have a link for you, but every time I post I get an error saying that my post is being held for moderation.

 

[gudujarlson]

Originally Posted by qcwtom .

Dave, that's really interesting.

What is the formula for calculating force based on power and cadence?

http://home.trainingpeaks.com/articles/cycling/quadrant-analysis.aspx

 

[daveryanwyoming]

Originally Posted by qcwtom .
...What is the formula for calculating force based on power and cadence?

Power = Torque (N.m) * angular velocity (rad/sec)

Pedal Torque = pedal force (n) * crank length (m) (pedal force = average effective pedal force per complete cycle of the cranks, peak pedal force ~ 2*aepf from Coyne, etc)
angular velocity = 2*pi*cadence/60

in metric units:

power (watts) = pedal force(n) * crank length (m) * 2*pi*rpm/60

rearranging for force:

pedal force (n) = power (watts)*60/[2*pi*rpm*crank length(m)]

and converting force to imperial units

pedal force (lbs) = pedal force (n)*(2.2/9.81) (newtons to kg mass to pounds force)

So for example:

300 watts, 172.5mm cranks, 90 rpm

Pedal force (n) = 300*60/(2*pi*90*0.1725) = 184 newtons aepf

or ~41.3 pounds aepf or based on known pedaling studies ~ 82 pounds peak pedal force during each cycle.

-Dave

 

[qcwtom]

Very cool. Thanks!