Power, cadence and energy usage

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Power, cadence and energy usage

Postby joomz » Sun Oct 06, 2013 4:08 pm

I was doing a boring recovery session on the rollers this afternoon. I decided to do a little experiment.
-if I maintain a constant speed (and therefore constant speed)
-but at different cadence (eg low cadence/hard gearing vs high cadence/low gearing)
how does heart rate respond?
Here's my ride data:
http://www.strava.com/activities/87189001

Time Speed Cadence Heart rate
30-35mins 50km/h 113rpm 150bpm
35-40mins 50km/h 98rpm 140bpm
40-45mins 50km/h 83rpm 134bpm
45-50mins 50km/h 106rpm 143bpm

I did the last one (cadence between first and second ones) just to check that the effect wasn't related to fatigue etc.

So, for a constant power/speed, my heart rate is a lot lower pushing a hard gear at lower cadence than it is pushing an easy gear at high cadence. I usually do my rides at cadences around 100rpm. Maybe this isn't all that efficient in terms of energy usage? Or is there a trade off between muscular fatigue (higher pushing bigger gears?) and energy usage (higher pushing smaller gears at high cadence)? Is there a way to determine optimum cadence for a given length of ride?
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by BNA » Sun Oct 06, 2013 7:23 pm

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Re: Power, cadence and energy usage

Postby sminns » Sun Oct 06, 2013 7:23 pm

joomz wrote:
So, for a constant power/speed, my heart rate is a lot lower pushing a hard gear at lower cadence than it is pushing an easy gear at high cadence.


I'm the same but I could easily pedal 100 for 5 hrs but not a harder gear at 80, it's like doing squats in a gym the more weight you use the less reps you can do.
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Re: Power, cadence and energy usage

Postby Alex Simmons/RST » Sun Oct 06, 2013 7:41 pm

joomz wrote:I was doing a boring recovery session on the rollers this afternoon. I decided to do a little experiment.
-if I maintain a constant speed (and therefore constant speed)
-but at different cadence (eg low cadence/hard gearing vs high cadence/low gearing)
how does heart rate respond?
Here's my ride data:
http://www.strava.com/activities/87189001

Time Speed Cadence Heart rate
30-35mins 50km/h 113rpm 150bpm
35-40mins 50km/h 98rpm 140bpm
40-45mins 50km/h 83rpm 134bpm
45-50mins 50km/h 106rpm 143bpm

I did the last one (cadence between first and second ones) just to check that the effect wasn't related to fatigue etc.

So, for a constant power/speed, my heart rate is a lot lower pushing a hard gear at lower cadence than it is pushing an easy gear at high cadence. I usually do my rides at cadences around 100rpm. Maybe this isn't all that efficient in terms of energy usage? Or is there a trade off between muscular fatigue (higher pushing bigger gears?) and energy usage (higher pushing smaller gears at high cadence)? Is there a way to determine optimum cadence for a given length of ride?


It's well established in scientific literature that efficiency (energy reaching cranks as a proportion of energy metabolised) drops as pedalling rate increases, but efficiency is rarely the aim, sustaining a higher power output usually is.

However I think it's a myth that lower pedalling rate for same power leads to greater muscular fatigue, although more research into that is needed for sub-maximal cycling, it's certainly not the case for maximal/sprint effort - although the research specifically into that is yet to be made public. Indeed it's precisely the opposite of what many believe to be the case. Once you understand the differences between muscle shortening velocity (i.e. pedal speed) versus frequency of muscle contractions (i.e. cadence) vs forces involved, it's the frequency of maximal muscle contractions that is the primary fatigue factor, not power or pedal force.
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Re: Power, cadence and energy usage

Postby singlespeedscott » Sun Oct 06, 2013 9:22 pm

joomz wrote:Here's my ride data:
http://www.strava.com/activities/87189001

Time Speed Cadence Heart rate
30-35mins 50km/h 113rpm 150bpm
35-40mins 50km/h 98rpm 140bpm
40-45mins 50km/h 83rpm 134bpm
45-50mins 50km/h 106rpm 143bpm


Buggar the effects of cadence. I want to know how you can maintain 50km/hr for 50min? :shock:
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Re: Power, cadence and energy usage

Postby joomz » Sun Oct 06, 2013 11:00 pm

50km/hr doesn't mean too much, it was on rollers with very little resistance and no aerodynamic drag of course ;-)

Good point sminns, I tend to start to feel fatigued if my cadence is too low. Not to mention sore knees. Interesting to think though if anything can be gained by slowing the leg velocity down a bit.

Alex, interesting stuff. So if you're doing 200km day after day, efficiency is more important than maximizing power isn't it? Because it's difficult eat enough to replace energy stores. With sprinting, is the implication that sprinting at a lower cadence will allow a longer sprint before exhaustion?
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Re: Power, cadence and energy usage

Postby Alex Simmons/RST » Mon Oct 07, 2013 1:28 am

joomz wrote:Alex, interesting stuff. So if you're doing 200km day after day, efficiency is more important than maximizing power isn't it? Because it's difficult eat enough to replace energy stores.

Maybe, maybe not. For the ultra endurance athlete, then yes, efficiency comes into play, but sustainable power matters more if how fast you ride those 200km matters, e.g. think pro cyclists in stage races. One thing that distinguishes pros is their phenomenal ability to digest large amounts of food during such events.

joomz wrote:With sprinting, is the implication that sprinting at a lower cadence will allow a longer sprint before exhaustion?

Yes, although:
- fatigue commences almost immediately and increases as one progresses, it's not like exhaustion simply arrives
- one needs to be careful when applying this as there are other factors in play wrt sprint performance
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Re: Power, cadence and energy usage

Postby Xplora » Mon Nov 18, 2013 10:21 pm

Joomz, I get similar results to you, lower cadence equals lower heart rate BUT I'm on borrowed time with the old concrete legs if I'm pushing a low gear at a high speed. I find it much easier to sit on the front at 100rpm and then change up a gear and spin 85rpm in the pack. I notice I typically have lower average long interval power with lower cadence BUT much stronger peak power in the short intervals - AKA I'm fresher and can push much much harder if I spin slow for as long as possible. I've noted a sign of my fitness seems to be how long can I spin slow. I can hammer along at 100rpm for a long time, but I can lift so much more that I prefer to spin slow when possible.
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Re: Power, cadence and energy usage

Postby g-boaf » Thu Nov 21, 2013 9:20 pm

Xplora wrote:Joomz, I get similar results to you, lower cadence equals lower heart rate BUT I'm on borrowed time with the old concrete legs if I'm pushing a low gear at a high speed. I find it much easier to sit on the front at 100rpm and then change up a gear and spin 85rpm in the pack. I notice I typically have lower average long interval power with lower cadence BUT much stronger peak power in the short intervals - AKA I'm fresher and can push much much harder if I spin slow for as long as possible. I've noted a sign of my fitness seems to be how long can I spin slow. I can hammer along at 100rpm for a long time, but I can lift so much more that I prefer to spin slow when possible.


Interesting. I went from being mashing the pedals at 75-80rpm to spinning at 95-110rpm. What I find is that I can manage around 95-100rpm with no problems for a long time, but more than that it just doesn't work. Too high a gear doesn't work either. It's a balancing act for me.

And it's all learning. I suppose the heart will get used to that spinning at high RPM over time.
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Re: Power, cadence and energy usage

Postby Xplora » Fri Nov 22, 2013 7:57 am

Well worth bearing in mind that I was spinning my bum off before dropping down to 85 again. My FTP test and 2x20 this week involved a lot of 85rpm work, but I do spend a lot of time at 100-110. I think it comes down to your training adaptions - the systems putting out 80-85 rpm are different to 110, and having the ability to switch is helpful. I would imagine boaf that once your knee is stable again, and you have some improved cardio from chasing GS KOMs, you would benefit from riding up a gear and grinding. I would also tell you to try to hit 180rpm on the trainer too, but I am a fairly weak rider lol

I have found my biggest motivation to spin is simply the guarantee that my knee will be hurt in 60 seconds of 65rpm in the seat. Less efficient to nurse injury etc :mrgreen:
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Re: Power, cadence and energy usage

Postby g-boaf » Fri Nov 22, 2013 8:32 am

My knee is now all good Leigh. After it mended, I ended up with some sort of quad injury on the left leg. Now that is recovered too (what next)- I'm free to go as quickly as I want to, which I did yesterday. :)

The highest RPM I ever saw was 140rpm, I don't know how people go faster than that. :mrgreen:

I know what it is like to ride around injuries. :roll:
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