The importance of crank length to the cyclist.

[TarmacExpert]

Submaximal O2 consumption isn't limiting (by definition). What it is is an indicator of ATP demand (turnover). In the context of the muscle's ability to generate ATP via oxidative phosphorylation, it is this ATP demand that dictates metabolic responses related to fatigue (e.g., accumulation of inorganic phosphate, depletion of glycogen). Since changing crank length doesn't alter how many mitochondria we have (or the ability of our cardiovascular system to provide O2), it could only act via changing ATP demand, i.e., efficiency - but efficiency is essentially independent of crank length, at least over a very broad range (i.e., from 145 to 195 mm...at least those are the extremes that I recall were tested).

I'm not able to dispute the specifics of the possible mechanisms, but your argument makes me think of the issue of cadence vs efficiency. As far as I'm aware, when people ride at max effort for an hour they do not use the most efficient cadence. I'm not aware that anyone has ever been able to get people to output more power for an hour by instead using their most efficient cadence. This suggests to me that there must be unrelated fatigue mechanisms at work.

 

[FrankDay]

My guess is this rider should get on shorter cranks. Clearly shorter cranks would help improve this rider's aerodynamics, wouldn't they?

http://www.youtube.com/watch?feature=player_embedded&v=Vdto2MAsU0s

 

[arracing8]

my two cent

I changed mine on my mtb. I tryed 180mm I was told wold be better for SS. I ran the same trail 7.87miles for the last 3months same time back to back laps. same time with in 10sec every time could not get faster 1lap 2lap 3 laps same time changed my crank arms to a 155mm drop 2mins off the very first ride lap2 same time I stayed 2mins faster my heart rate lowered too so I went up in my gear same gear set up that i try before and it didnt help now with the gear changed and the 155mm i drop :45sec for a total of 2:45 off my time in 2 days wow i going to keep playing now 145mm testing soon. ( I am 5'4" 170lbs and riding avg 14mph on that trail) soon going to look and changing my road bike crank too. I believe it help me

 

[CoachFergie]

That story doesn't match the research on the area of crank length and performance. I would disagree with a rider of your height riding 180mm cranks anyway but the published data would suggest that something else caused the difference in performance.

 

[arracing8]

I did have 175mm and never got as fast as i am now my cadence is up by 15 to 18 more

 

[CoachFergie]

Again nothing in that indicates that crank length is the cause for the change in performance.

At the start of this train wreck of a thread Frank told the story of a rider who improved his time in a Hill race by over an hour from the previous year. What he failed to share was how the course was ridden in reverse and if I recollect was a little bit shorter.

This is why we look at the research not personal anecdotes when selecting equipment, deciding on sizing and determining what experiments we wish to perform as part of the performance process.

 

[Boeing]

just who in the F all is "we" coachie?

all this coming from the so called coach who offers nothing more than his own explanations as evidence.


coach em up Bogan

 

[cyclingwombat]

just who in the F all is "we" coachie?

all this coming from the so called coach who offers nothing more than his own explanations as evidence.


coach em up Bogan

Read the thread - there are quite a number of people who pointed out exactly that flaw in Frank's initial presentation. Question: What have YOU contributed to this thread other than your monthly visit to attack CoachFergie?

 

[Black-Balled]

Of course ...people clicking to see where the soap opera has gone now...

I am purely here for the soap opera

 

[TarmacExpert]

This is why we look at the research not personal anecdotes when selecting equipment, deciding on sizing and determining what experiments we wish to perform as part of the performance process.

Published research is useful, but I think it is also important to perform personal experiments and to think about the underlying principles behind things. Most studies look for a change in the average, based on the assumption that all subjects will be affected in the same way. This can cause a false negative, where no change in the average is composed of a beneficial impact on some subjects and an adverse impact on others.

There has been some good discussion in this thread, and combined with my personal experimentation and further thinking, I have learned a lot. E.g. I moved from 165mm to 175mm cranks, and noticed that I still seem to have my thighs coming up much lower at the top of the pedal stroke compared to most people. I have concluded that this is because I have relatively long femurs compared to the norm. A further effect of this is that even with 175mm cranks and a saddle to pad drop of 12.5cm, my knees don't get up behind my elbows. Andy Coggan has shared some info on what he gained from going "low sit", whereby both pads and saddle are lowered, but I have a feeling that was most likely in the context of his upper legs already being behind his arms at the top of the pedal stroke. In my situation, with my knees a fair bit below my elbows, I think I actually gain more than Andy did for each cm I lower my saddle and pads, so I am working on lowering them both in small increments, giving myself time to adapt to each change.

Resulting personal anecdote - 19:46 for 10 miles on 31st May on the same course and with the same power that got me 20:23 on 17th May.

I intend to try to lower pads and saddle even further yet. It feels like the limiter for me is going to be knee angle rather than hip angle.

 

[CoachFergie]

I'm all for personal experimentation but there has to be a certain basis before I commit my time, energy and money to testing anything. More important when it is the clients time, energy and money. I have yet to see any data to make me consider testing crank length. Much bigger fish to fry.

 

[FrankDay]

Exciting news. Some engineers in Australia have been working on putting power into the crank arms of the PowerCranks so that users can get what each leg is doing independently around the full circle. I am told that the power meter will be more accurate than the SRM but, of course, give the entire data for each ride for both legs independently. When these are available it should be easy for cyclists to see what technique works best for them and what crank length does to both power and technique. If riding indoors the rider will be able to see what is going on real time on a computer screen. If outdoors, the ride can be downloaded for intense analysis later, so I am told. It works with Garmin heads so some data is available during the ride but not sure how detailed it is right now on that unit.

Anyhow, I thought I would show you what a screen shot looks like so you can see what kind of data is available. I find it interesting they are showing both torque and instantaneous power around the circle. In this instance when the left leg is negative on the upstroke it costing about 5% of the instantaneous pushing power whereas the right leg costs as much as 10% of the pushing power. And the left leg is really late on pushing, still giving negative power well over the top. Such a subtle asymmetry and weakness would never be picked up on a regular power meter.

Anyhow, I would like to see this available by the holidays but I suspect next spring is more likely. Cost (including the basic adjustable PowerCranks) should be about $3k. I get a prototype pair next week for testing and comment.

Here is the screen shot. Enjoy.

 

[CoachFergie]

When these are available it should be easy for cyclists to see what technique works best for them and what crank length does to both power and technique.

This has already been studied.

Such a subtle asymmetry and weakness would never be picked up on a regular power meter.

Because the purpose of a power meter is to measure power.

Anyhow, I would like to see this available by the holidays but I suspect next spring is more likely. Cost (including the basic adjustable PowerCranks) should be about $3k. I get a prototype pair next week for testing and comment.

We look forward to publication of data.

 

[Elagabalus]

Exciting news. Some engineers in Australia have been working on putting power into the crank arms of the PowerCranks so that users can get what each leg is doing independently around the full circle. I am told that the power meter will be more accurate than the SRM but, of course, give the entire data for each ride for both legs independently. When these are available it should be easy for cyclists to see what technique works best for them and what crank length does to both power and technique. If riding indoors the rider will be able to see what is going on real time on a computer screen. If outdoors, the ride can be downloaded for intense analysis later, so I am told. It works with Garmin heads so some data is available during the ride but not sure how detailed it is right now on that unit.

Anyhow, I thought I would show you what a screen shot looks like so you can see what kind of data is available. I find it interesting they are showing both torque and instantaneous power around the circle. In this instance when the left leg is negative on the upstroke it costing about 5% of the instantaneous pushing power whereas the right leg costs as much as 10% of the pushing power. And the left leg is really late on pushing, still giving negative power well over the top. Such a subtle asymmetry and weakness would never be picked up on a regular power meter.

Anyhow, I would like to see this available by the holidays but I suspect next spring is more likely. Cost (including the basic adjustable PowerCranks) should be about $3k. I get a prototype pair next week for testing and comment.

Here is the screen shot. Enjoy.

Great news, Frank!

When can I expect that royalty check?

http://forum.cyclingnews.com/showthread.php?p=517017#post517017

 

[FrankDay]

Great news, Frank!

When can I expect that royalty check?

http://forum.cyclingnews.com/showthread.php?p=517017#post517017

I am afraid we weren't able to figure out how to incorporate a $200 price drop per your suggestion, so no royalty check I am afraid. If you could tell us how to get that $200 price drop into this system it would be worth a royalty check. Of course, it wouldn't do you much good as Fergie would do everything he could to prevent us selling a single unit, regardless of the cost.

We looked at this a long time back and it was simply too difficult for us. Thankfully some aerospace engineers decided to take on this job themselves. This is not a simple problem. Look at the problems all the others trying to do pedal based systems are having bringing them to market. It is my prediction that if this system and the pedal based systems are as good as they promise that it will transform, over the next 5 years, how cyclists think about pedaling. We will see. Either way, knowledge is power.

 

[CoachFergie]

We looked at this a long time back and it was simply too difficult for us. Thankfully some aerospace engineers decided to take on this job themselves. This is not a simple problem.

The Germans have been using a crank based system on track for quite a few years. It's nothing new. I saw a pair of crank arm based power meter (with adjustable length crank) up at Massey University last year.

Look at the problems all the others trying to do pedal based systems are having bringing them to market. It is my prediction that if this system and the pedal based systems are as good as they promise that it will transform, over the next 5 years, how cyclists think about pedaling

.

All the things you have promised have already been studied.

From a physical performance position the dependant variable will still be the power produced. How the power is applied through the pedal stroke and manipulation of crank length has been well researched using force measuring pedals and other performance measures. Any manipulations showed no significant advantage over current recommendations of how one should pedal or what crank length should be selected.

 

[Boeing]

allow me to sum up this thread for first time viewers.

crank arm length is important.

no its not

yest it is

no

yes

how do you know

i just do how do you know

works for me

thats not enough data. it works for may riders

thats not enough data

yes it is because Im a coach

no its not

yes it is

no its not

yes

no

 

[FrankDay]

The Germans have been using a crank based system on track for quite a few years. It's nothing new. I saw a pair of crank arm based power meter (with adjustable length crank) up at Massey University last year.

I said it was simply too difficult for us, I didn't say it was too difficult for everyone. In fact, I also have seen a crank based PM many years ago. However, not a single one of these as made for mounting on a bicycle that was meant to go on the road nor placed on independent cranks. We simply didn't have the expertise in house to do this nor the money to contract this to be done.

All the things you have promised have already been studied.

From a physical performance position the dependant variable will still be the power produced. How the power is applied through the pedal stroke and manipulation of crank length has been well researched using force measuring pedals and other performance measures. Any manipulations showed no significant advantage over current recommendations of how one should pedal or what crank length should be selected.

Really? I thought the "dependent variable" of importance to cyclists was how fast the bicycle is going relative to everyone else, power being only one part of that equation (part of the analysis that started this thread). Either way, I believe you have made that point before. Not everyone is in agreement with your position. So, why don't you let those who might think differently to continue with our apparent delusion that technique might actually be important to the power production/energy utilization efficiency equation. If you are correct, that it has already been proven that knowing this stuff will be a complete waste of time, then I am sure that all that work by Garmin, Look, and the people who did this work for us, will be for naught as absolutely no one will pay the extra money for this extra information. We will see. At least all of your athletes can breathe easy knowing that you are not going to waste any of their time or energy exploring this aspect of cycling with them.

 

[sciguy]

I see one shortfall of this system compared to the potential information that might be provided by a properly functioning Garmin pedal based system. The crank arm based system will be unable to "see" forces applied other than those tangential to the crank axle. It will "sense" positive or negative torque on each side but will miss forces that are not tangential to the axle. For example if a rider was applying a significant upward force when the pedal was already at TDC or downward one when the pedal is at BDC these will not be measured. It may still provide some interesting data but nearly as much as a pedal based system could potentially offer.

YMMV,

Hugh

 

[FrankDay]

I see one shortfall of this system compared to the potential information that might be provided by a properly functioning Garmin pedal based system. The crank arm based system will be unable to "see" forces applied other than those tangential to the crank axle. It will "sense" positive or negative torque on each side but will miss forces that are not tangential to the axle. For example if a rider was applying a significant upward force when the pedal was already at TDC or downward one when the pedal is at BDC these will not be measured. It may still provide some interesting data but nearly as much as a pedal based system could potentially offer.

YMMV,

Hugh

No, that is not true. A properly designed crank based system should be able to see all the forces that a pedal based system should be able to see. It is simply a matter of interpreting the data properly.

The developers of this system make a very high end exercise bike in which they originally had two SRM systems installed to give the left right data. This system would only be capable of doing the tangential analysis, which is what the graph shows. They developed the PowerCranks system as a much cheaper alternative that would give them even more data and, they are telling me, is even more accurate than the SRM. Now, whether this data is presented to the user or not is a different story. Not sure what they will do here. Garmin and Look have similar issues, how to best present the data they are collecting. If it is too complicated no one will be able to use it which will hurt sales. Perhaps, they will choose to have simple output with the option of more detailed analysis for those who need it. We will see. I know my people are still working on this.

The drawback of my system is few will choose to race on it. But, then, is that really a drawback? I doubt any will look down during a race, take a close look at their output device, and say, "Ooops, notice I am not very tangential, need to change that!" I see all this extra information as training useful, not race day useful.

 

[sciguy]

No, that is not true. A properly designed crank based system should be able to see all the forces that a pedal based system should be able to see. It is simply a matter of interpreting the data properly.

Care to wager a bet on that? Perhaps a beer in Kona this October?

Hugh

 

[FrankDay]

Care to wager a bet on that? Perhaps a beer in Kona this October?

Hugh

Sure, I'll take that bet. But, before you bet, understand how the system is supposed to work. Let's take a simple two strain gauge rigid crank arm system. A purely tangential force should put one gauge in extension and the other in an equal amount of compression. If the applied force is not tangential, the extension and compression forces will not be equal as both gauges will be either stretched or compressed equally by the radial component. A purely radial force puts both gauges in an equal amount of extension or compression. If we know where the force is applied in relation to the gauges, there is only one solution and it will give both the tangential and radial components of the applied force.

Pretty simple in theory. Somewhat more difficult to carry off in practice but perfectly doable. If I have missed something, let me know. Whether I receive or buy a beer I would look forward to talking with you in Kona.

 

[FrankDay]

Another anecdotal report on this topic: "I've started racing track, and in two nights, I won 4 races on 145mm cranks. So, apparently they don't hurt the sprint."

 

[sciguy]

Sure, I'll take that bet. But, before you bet, understand how the system is supposed to work. Let's take a simple two strain gauge rigid crank arm system. A purely tangential force should put one gauge in extension and the other in an equal amount of compression. If the applied force is not tangential, the extension and compression forces will not be equal as both gauges will be either stretched or compressed equally by the radial component. A purely radial force puts both gauges in an equal amount of extension or compression. If we know where the force is applied in relation to the gauges, there is only one solution and it will give both the tangential and radial components of the applied force.

Pretty simple in theory. Somewhat more difficult to carry off in practice but perfectly doable. If I have missed something, let me know. Whether I receive or buy a beer I would look forward to talking with you in Kona.

It sounds pretty nifty in theory and I'll admit it may well work. In regards to making it actually work in other than tangential force measurement, it would seem to share many of the same computational complexities as the Garmin Pedal system.

I would love to see the patent drawings from Breakaway Innovations but haven't had any luck yet.

Considered yourself very likely owed a beer but I a call dibs on playing with a set of the stain gauge cranks if you have a set there.

Hugh

 

[CoachFergie]

Really? I thought the "dependent variable" of importance to cyclists was how fast the bicycle is going relative to everyone else,

Still can't tell the difference between a process variable and an outcome variable.

power being only one part of that equation (part of the analysis that started this thread).

Yes we know that using a short crank allowed a independent crank user to ride a race over an hour faster compared to the previous year. What you failed to mention was that the race was a different length and ridden the opposite way to the previous year.

Either way, I believe you have made that point before. Not everyone is in agreement with your position.

The position supported by all the research?

So, why don't you let those who might think differently to continue with our apparent delusion that technique might actually be important to the power production/energy utilization efficiency equation.

Because these new cranks will supply no new data that hasn't been presented before.

If you are correct, that it has already been proven that knowing this stuff will be a complete waste of time, then I am sure that all that work by Garmin, Look, and the people who did this work for us, will be for naught as absolutely no one will pay the extra money for this extra information.

One of my riders had the Look/Polar system for a week and has brought a Quarq as the Look/Polar system had many limitations. Garmin has been bogged down with technical issues. The application of data from most studies on pedalling technique or crank length have been minimal to non-existent compared to research on training methods, recovery and diet.