Power, cadence, and hills

[Raketmensch]

So I just got my new PowerTap. Love it so far... no technical issues, it just works. And, geek that I am, I'm really enjoying digging into the data from my workouts.

My racing season is now over, I've just spent about three weeks on vacation completely off the bike (though getting lots of exercise), and now I'm starting on several months of endurance rides.

Anyway, here's an interesting thing I noticed from today's workout that maybe one of you power experts can explain.

There were two segments of my workout that are of interest... call them A and B. Segment A came about half an hour into the workout when I was fully warmed up, segment B came a bit later. Each was exactly 8 minutes long, and for each my average heart rate was 152 bpm (my max is ~183). Heart rate fluctuated by no more than a few bpm during each segment (in fact, it was very close to 150 for the whole workout). Segment A was on a flat stretch of road, with an average cadence of 98 rpm. Segment B was on a hill which I climbed (seated) in my lowest gear at an average cadence of 66 rpm. I would say that perceived effort was about the same for the two segments.

The interesting thing is that my power (which was also very steady over both segments) averaged 25 watts higher on the uphill segment (B) than on the flat segment (A).

So if my heart rate was identical for the two segments, why was my power so much higher climbing the hill? Was it because my cadence was lower? And is this a hint that if I ride on the flat at a lower cadence I'll see better power numbers for a given heart rate? Or was it something else?

Any thoughts would be greatly appreciated!

 

[mullerrj]

The interesting thing is that my power (which was also very steady over both segments) averaged 25 watts higher on the uphill segment (B) than on the flat segment (A).

So if my heart rate was identical for the two segments, why was my power so much higher climbing the hill? Was it because my cadence was lower? And is this a hint that if I ride on the flat at a lower cadence I'll see better power numbers for a given heart rate? Or was it something else?

Any thoughts would be greatly appreciated!

Send me your Power Files.

I think the reason why your hill power wasn't that much higher than on the flats was because it wasn't very much of a hill (4-6% grade I'm guessing) and because you were riding at a much lower cadence. I bet you if you attacked the same hill (with a higher cadence), next time, you'd see a bigger delta in your average watts (much greater than 25 watts avg.) and much higher power output.

And, if you ride the flat a a lower cadence (next time), you won't see better power numbers, but you will see a lower HR. Try it..you'll see. Rob

 

[Raketmensch]

I think the reason why your hill power wasn't that much higher than on the flats was because it wasn't very much of a hill (4-6% grade I'm guessing) and because you were riding at a much lower cadence. I bet you if you attacked the same hill (with a higher cadence), next time, you'd see a bigger delta in your average watts (much greater than 25 watts avg.) and much higher power output.

Sorry, I guess I didn't explain myself adequately. Certainly you're right that if I attacked the hill harder I'd see higher power numbers. But I wasn't asking why my power wasn't higher on the hill (which is 8% average grade). Instead, given that my heart rate was identical on the two segments, I'm curious as to why my power numbers were different at all.

You did predict that by riding at a lower cadence on the flat I would see a lower heart rate for a given power output, and based on today's data I suspect that that's true. I'm going to try it as you suggest on subsequent rides.

The thing I'm really wondering is whether or not this all means that I should be riding at a somewhat lower cadence than my usual 95-100 rpm.

 

[mullerrj]

Sorry, I guess I didn't explain myself adequately. Certainly you're right that if I attacked the hill harder I'd see higher power numbers. But I wasn't asking why my power wasn't higher on the hill (which is 8% average grade). Instead, given that my heart rate was identical on the two segments, I'm curious as to why my power numbers were different at all.

You did predict that by riding at a lower cadence on the flat I would see a lower heart rate for a given power output, and based on today's data I suspect that that's true. I'm going to try it as you suggest on subsequent rides.

The thing I'm really wondering is whether or not this all means that I should be riding at a somewhat lower cadence than my usual 95-100 rpm.

So, let me see if I got it: what you're wondering is why if HR is the same, whether riding on the flats vs. the hills, why isn't Power Output the same as well for the same HR? Yes/No?

If that's what you're asking, than it leads to a similar question: whether a lower cadence with a bigger gear on the flats might suit you better than a smaller gear and high cadence on the flats- right? If that's true, try it next time on the flats. Go back and ride the same flats at the 90-100 rpm in an easy gear, then turn around go back and repeat it at 65-75 rpm with a harder gear and compare: overall time, avg. speed, avg. power, etc. Do a 5 mile Time Trial or something. I'd be interested in knowing your results. I'll do the same and have my buddy do the same too, and we'll compare data. I'm guessing you'll find an optimized cadence somewhere in between the two..closer to the 90-100 rpm. BTW, the "best" cadence topic has come up a lot on the cycling forums. I can only say, based on what I've read..and researched..that everyone has an "optimized" cadence..and that most elite athletes, that I've tested and witnessed have all been between the 90-100 rpm range. Anyway, try it and get back to me..I'm interested in knowing too. Good subject. Rob

 

[Animator]

Cardiac drift, if I understand it correctly, might explain it...

 

[Raketmensch]

Cardiac drift, if I understand it correctly, might explain it...

I don't think so. Cardiac drift is the tendency for heart rate to rise with time during a workout, other factors (like power) being equal. So if I were experiencing cardiac drift, for equal heart rates I would have expected lower power output in the later segment of the ride (which was the hill climb). What I observed was the other way around.

 

[Raketmensch]

So, let me see if I got it: what you're wondering is why if HR is the same, whether riding on the flats vs. the hills, why isn't Power Output the same as well for the same HR? Yes/No?

Yes, exactly.

If that's what you're asking, than it leads to a similar question: whether a lower cadence with a bigger gear on the flats might suit you better than a smaller gear and high cadence on the flats- right?

Precisely.

If that's true, try it next time on the flats. Go back and ride the same flats at the 90-100 rpm in an easy gear, then turn around go back and repeat it at 65-75 rpm with a harder gear and compare: overall time, avg. speed, avg. power, etc. Do a 5 mile Time Trial or something. I'd be interested in knowing your results.

Yes, I'm going to try exactly that, sometime in the next week or so. If I get results I can make any sense out of, I'll post them here.

I can only say, based on what I've read..and researched..that everyone has an "optimized" cadence..and that most elite athletes, that I've tested and witnessed have all been between the 90-100 rpm range.

Yes, I've read and heard the same thing. And I know that I'm most comfortable in the 90-100 range... that's where I spend most of my time in a normal workout. But what the heck, it's the off season, and it's a good time to experiment.

 

[Roadie_scum]

So I just got my new PowerTap. Love it so far... no technical issues, it just works. And, geek that I am, I'm really enjoying digging into the data from my workouts.

My racing season is now over, I've just spent about three weeks on vacation completely off the bike (though getting lots of exercise), and now I'm starting on several months of endurance rides.

Anyway, here's an interesting thing I noticed from today's workout that maybe one of you power experts can explain.

There were two segments of my workout that are of interest... call them A and B. Segment A came about half an hour into the workout when I was fully warmed up, segment B came a bit later. Each was exactly 8 minutes long, and for each my average heart rate was 152 bpm (my max is ~183). Heart rate fluctuated by no more than a few bpm during each segment (in fact, it was very close to 150 for the whole workout). Segment A was on a flat stretch of road, with an average cadence of 98 rpm. Segment B was on a hill which I climbed (seated) in my lowest gear at an average cadence of 66 rpm. I would say that perceived effort was about the same for the two segments.

The interesting thing is that my power (which was also very steady over both segments) averaged 25 watts higher on the uphill segment (B) than on the flat segment (A).

So if my heart rate was identical for the two segments, why was my power so much higher climbing the hill? Was it because my cadence was lower? And is this a hint that if I ride on the flat at a lower cadence I'll see better power numbers for a given heart rate? Or was it something else?

Any thoughts would be greatly appreciated!

It's absolutely normal that riding at a lower cadence produces a lower heart rate for a given power (or the same heart rate for a higher power). However, there is no particular reason to target a high power/heart rate ratio. Just ride at whatever cadence is comfortable and try to increase your power at durations relevant to your target event.

 

[DesFlurane]

What's heart rate got to do with anything?

Disclaimer: I used to have a heart rate but the strap is now in my sock draw

 

[Animator]

I don't think so. Cardiac drift is the tendency for heart rate to rise with time during a workout, other factors (like power) being equal. So if I were experiencing cardiac drift, for equal heart rates I would have expected lower power output in the later segment of the ride (which was the hill climb). What I observed was the other way around.

Gotcha. I misunderstood.

 

[Raketmensch]

It's absolutely normal that riding at a lower cadence produces a lower heart rate for a given power (or the same heart rate for a higher power).

Interesting. I hadn't known that before I got my power meter, but it's very evident in the data. I wonder what the physiological explanation for that is.

However, there is no particular reason to target a high power/heart rate ratio.

And that's the key concept that I'm realizing I need to fully wrap my head around. Until I got my PowerTap I've trained exclusively with heart rate, and I'm very used to thinking of heart rate as the measure of how hard I'm working. But of course power is the real measure of how hard I'm working, by definition... and heart rate is only one among numerous possible measures of how my body's responding to the act of doing that work.

I think I'm starting to get it.

 

[Roadie_scum]

Interesting. I hadn't known that before I got my power meter, but it's very evident in the data. I wonder what the physiological explanation for that is.

Efficiency (measured as the oxygen cost of a given power) tends to be lower at a lower cadence. This does not, however, necessarily translate into a performance benefit. Bottom line - in general there is no need to target high or low cadences, just ride where you are comfortable.

And that's the key concept that I'm realizing I need to fully wrap my head around. Until I got my PowerTap I've trained exclusively with heart rate, and I'm very used to thinking of heart rate as the measure of how hard I'm working. But of course power is the real measure of how hard I'm working, by definition... and heart rate is only one among numerous possible measures of how my body's responding to the act of doing that work.

I think I'm starting to get it.

Sounds like you are onto it! Good work...

 

[frenchyge]

Interesting. I hadn't known that before I got my power meter, but it's very evident in the data. I wonder what the physiological explanation for that is.

You should also be aware that the heart varies its stroke volume in addition to varying its stroke rate. Just because HR is lower at lower cadences doesn't mean that it's pumping less blood.

I seem to recall that HR's (and breathing rate's) correlation to cadence is a parasympathetic response of the central nervous system to the peripheral nervous system's more rapid signals to the lower body.... or that might just be some BS that came to me in a dream one night.

But of course power is the real measure of how hard I'm working, by definition... and heart rate is only one among numerous possible measures of how my body's responding to the act of doing that work.

I think I'm starting to get it.

Yep. The real trick is to not act smug when you find someone who's still clinging to HR as their primary fitness indicator.

 

[rmur17]

Efficiency (measured as the oxygen cost of a given power) tends to be lower at a lower cadence.
errr ... you mean Efficiency tends to be higher at lower cadence don't you?

This does not, however, necessarily translate into a performance benefit. Bottom line - in general there is no need to target high or low cadences, just ride where you are comfortable.



Sounds like you are onto it! Good work...

to the OP: HR varies for so many reasons not directly related to output power and one of the strongest influences is cadence. Ditch the HRM now or even sooner! To plagiarize R. Chung: "HR is a red herring"

 

[Roadie_scum]

Efficiency (measured as the oxygen cost of a given power) tends to be lower at a lower cadence.
errr ... you mean Efficiency tends to be higher at lower cadence don't you?

Oops. I either meant oxygen cost is lower at a lower cadence or I meant efficiency is higher at a lower cadence. I definitely didn't mean efficiency is lower at a lower cadence, like I wrote!

Thanks for picking that up Rick.

 

[jsirabella]

Not to keep this thread going but I am interested that if you have been diagnosed with a heart murmur or my mom used to call it an extra beat, how does that effect going by HR? I would be intersted also if things like pidgeon toe or bow legged makes a difference in how eell a person can ride?

Also I had been uising an HR strap for many years and I find at times that now that I am training with power, it can realyl feel constricting and makes me feel sore. You really feel the data is useless and I can ditch it entirely now?

-js

to the OP: HR varies for so many reasons not directly related to output power and one of the strongest influences is cadence. Ditch the HRM now or even sooner! To plagiarize R. Chung: "HR is a red herring"

 

[Philsybob]

I have been training with a power meter now for about a year and have seen quite dramatic differences in TT's with lower cadences increase from 300 watts to 325 watts in a week by changing my cadence from 90-100 to 70-80.

But...

I have also discovered that I cannot train at this cadence for long periods, as the effort is more "neuro-muscular" and requires longer to recover from.

So I am training at a higher cadence (able to do 2 x 20 minute efforts @ 300 watt now) and then when I need to extract a few more watts may well resort to the lower cadence.

Point of the post - don't be fooled into into training at low cadences thinking it is more efficient.