Torque and RPE? Or maybe not?

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As a long time reader, two time poster and relatively new user of a PowerTap I am hoping you collectively may be able to help me out...

My post revolves around the link between torque and RPE and the implications for my friends training plan.

My training partner and I were on the trainer tonight doing 6 sets of 3 min at FTP*117% with 3 min recovery (part of a session from Andy and Hunters book... thanks guys). My partner really struggled with her first 4 intervals, but was pretty consistent with: NP ~275W (aiming for 290W) and cadence ~85 rpm. For these first 4 she felt her cadence was too low but she couldn't 'get on top' of a faster (lower) gear. After the 4th interval she set the resistance on the traininer to a harder setting and felt much more comfortable for the last two intervals. For these two her NP was ~270W, cadence was ~88 rpm but her RPE was 'much easier' (sorry Mr Borg, we didn't use your scale).

Once we downloaded the file we could see a 'big' difference in torque (~8.8 Nm before and ~10.5 Nm after adjusting the trainer).

So... here come the questions!

Is the change in RPE a result of a small drop in power (~5 W) and a small increase in cadence (~3 rpm)
Or... is the difference in torque (8.8 Nm vs. 10.5 Nm) significant, could that be the reason for the change in RPE?
If the change in torque is a factor, what does this mean for my friends training plan...? Does she need to work on developing power at a lower torque?
Some background (if needed). My friend is 34, ~60kg and a former elite long distance triathlete who is in the midst of change from triathlon to mountainbiking/cyclo-cross. We have identified (using power profiling) that her 5 second, 1 min and 5 min power need to be improved. Her last measured FTP is 250W. We plan to measure again next week as we feel it's improved to about 265W. She feels she struggles to push 'big gears'. Yes, I know that's not very scientific :rolleyes: .

Thank you very much for your time, apologies for the long post .

My partner really struggled with her first 4 intervals, but was pretty consistent with: NP ~275W (aiming for 290W) and cadence ~85 rpm. For these first 4 she felt her cadence was too low but she couldn't 'get on top' of a faster (lower) gear. After the 4th interval she set the resistance on the traininer to a harder setting and felt much more comfortable for the last two intervals. For these two her NP was ~270W, cadence was ~88 rpm but her RPE was 'much easier' (sorry Mr Borg, we didn't use your scale).

Once we downloaded the file we could see a 'big' difference in torque (~8.8 Nm before and ~10.5 Nm after adjusting the trainer).

One missing piece here is that she also changed to a lighter gear without telling you (or maybe you just didn't tell us... ;) ), since the hub torque was higher, cadence was higher and yet power was lower. IOW, wheel speed was lower even though cadence was higher.

PT torque is measured at the hub, and must be multiplied by the gear ratio to find torque at the cranks.


So... here come the questions!

Is the change in RPE a result of a small drop in power (~5 W) and a small increase in cadence (~3 rpm)
Or... is the difference in torque (8.8 Nm vs. 10.5 Nm) significant, could that be the reason for the change in RPE?
If the change in torque is a factor, what does this mean for my friends training plan...? Does she need to work on developing power at a lower torque?
In combination with the first point, it sounds like she was a bit frustrated by the laborious 'overgeared' feeling during the first 4 intervals. By increasing the resistance and shifting to a lower gear, it probably felt more natural to her. If you've been following the recent "20min Power" thread, then you've probably read that crank inertia affects a rider's self-selected cadence, and by shifting to a lower gear her crank inertia was reduced. In that lower gear, her self-selected cadence was closer to the 88 rpm she needed to generate 270w at that trainer resistance. Complicated answer, but basically if just felt more natural.

As far as training goes, if she's an elite triathlete then there's no reason not to let her train in the way that feels natural, unless she's trying to adapt herself for another type of event. Leave the trainer setting where it is now.

Thank you very much for your time, apologies for the long post . Good 3rd post. Happy lurking. :)

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PT torque is measured at the hub, and must be multiplied by the gear ratio to find torque at the cranks. Ahh! i didn't think of that. Thank you for your answer Frenchy, it was just what I was hoping for, clear and helpful.

As far as training goes, if she's an elite triathlete then there's no reason not to let her train in the way that feels natural, unless she's trying to adapt herself for another type of event. Leave the trainer setting where it is now. She is trying to adapt to a new discipline, cyclocross/mtb. How might this affect the torque/cadence/power relationship of her sessions? We've vaguely chatted about pushing a bigger gear in some sessions... what might you (or others) suggest? (I'm afraid power workouts are limited to the trainer & road bike).

[color=black]Good 3rd post. Happy lurking. :)It has a name? Sounds a bit dodgy ;)