Thanks Frank. I tried 155's recently (I'm 6ft 3 by the way) and anecdotally found they were easiers to access to peak wattages due to their increased acceleration although I found them harder to maintain it (for obvious reasons). I found it interesting that the muscle firing cycle was much shorter (it felt more like a constant application of load as opposed to a load/unload).

Do you feel that there is a worthwhile relationship or corrolation between femur length and crank length ?

...and don't forget crank length ;-)

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http://bikeblather.blogspot.com/

I am coming to the conclusion that femur length or almost anything else doesn't make very much difference in this regards. However, one thing that might make a difference is how flexible the person is. Can your hands only make it to the middle of your shins when trying to touch your toes or can you put your palms flat on the floor? The more flexible you are the longer the cranks you can probably ride without detriment I would guess.

I also am about 6'3" and have become very happy with 165 cranks. It took a week or two for the legs to adapt to the shorter length but once there it seemed natural. I then started trying to reduce the cadence. Again, same issue, takes a little while to adapt then it seems natural. I seem to be riding faster than before and I don't know whether this is due to improved power or improved aerodynamics or some combination as I don't have a PM.

Am about to experiment with 155's. Some day I will achieve a crank length that is too small or a cadence that is too slow (at least for me) but I haven't reached it yet. I would encourage everyone to experiment with this stuff this off season and see what happens.

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Frank,
An original Ironman and the Inventor of PowerCranks

Tom, the Force-Velocity curve is a muscle property, therefore it has nothing to do with crank length. The force is the force developed by the muscle, and the velocity is the speed of contraction of the muscle.

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Giovanni Ciriani
http://www.GlobusSHT.com

I understand that...but you were talking about cycling cadence, which for a given pedal force/pedal (tangential) speed (i.e. for a given point on the muscle force-velocity curve) is ENTIRELY determined by the crank length.

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http://bikeblather.blogspot.com/

I understand that...but you were talking about cycling cadence, which for a given pedal force/pedal (tangential) speed (i.e. for a given point on the muscle force-velocity curve) is ENTIRELY determined by the crank length.[/reply]Tom, I see what you mean. My reasoning goes the other way around: on the force-velocity curve of the muscle you determine the optimum point. Then for that combination of force and speed of the muscle you determine the crank length and the speed of the bike.

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Giovanni Ciriani
http://www.GlobusSHT.com

Tom, I see what you mean. My reasoning goes the other way around: on the force-velocity curve of the muscle you determine the optimum point. Then for that combination of force and speed of the muscle you determine the crank length and the speed of the bike.[/reply]
...and don't forget the rest of the "leverage ratio" between the crank and the ground ;-)

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http://bikeblather.blogspot.com/

Ok, first ever post here (man, it's noisy).


It seems you don't have the whole picture clear regarding the mechanics of the pedaling.
First, there are the conscious/unconscious muscle contraction forces that produce the driving power.
Second, there are the mechanical forces from the dynamics/motions of the limbs and cranks/pedals.


Read this out loud:
Those two groups of forces are independent and superimposed

Mechanical forces:
Yes, there is a metabolic cost to have to apply the forces fast (and maybe precise in time, depending on technique) with a high cadence/pedal velocity.

No, there is (virtually) no metabolic cost to continually stop and accelerate the limbs in a pendulum or circular way.

You focus on the fact that the thighs are stopped and accelerated. There's a force required to accelerate the thighs, yes. That same kind of force, but the other way, decelaration, is being put to good use by adding extra pedal force when the thigh is being stopped by the crank. Frank, ponder on this...

On top of that, the cranks work as elastic KE converters. Part of the momentum of the thighs is converted to a similar (but lower) momentum of the shanks (as in lower legs).
Thighs stopped = fast shanks.
Thighs fast = shanks stopped.

To complete the picture, the feet and shoes rotate with basically constant KE/momentum.

Zero sum.


Muscle forces:
With just a basic level of technique and a suitable cadence, one can fire the muscles in symphony with the given motion of the pedals. Given, in the sense that the KE of the "vehicle" is in the order of 10-100 times the energy of one "pedal push", meaning you can't change the motion of the pedal "within the push" much no matter what you do.

So, the motion of the pedals is given, and hence the mechanical forces from the motions of the limbs. Superimposed on that are the muscle forces that do the actual work. This superimposion works perfect and unnoticed for a wide variety of cadences and power levels since the muscle forces always "overshines" the mechanical forces and the system never "backlashes". If the cranks are connected, one leg can help the other.

Very high cadence:
The system can fall apart in the very high cadence/lower power scenario. As the cadence increases, so does the acceleration of the thighs, proportional to (crank length) x (cadence)^2. If the muscle forces that makes it through to the pedals are lower that the acceleration forces required, the superimposion becomes "negative" and there is a "discontinuity" in the motion, unless you are riding a fixed (which will rob "vehicle KE" to get it done).


Clear?

 
If the Naval Academy couldn't teach him elementary physics...what makes you think that you (or I...or anyone else) can? ;-)

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http://bikeblather.blogspot.com/

"This study demonstrated that elite cyclists perform best at their most efficient cadence despite the maximal energy turnover rate being larger at a higher cadence."

What wasn't in the abstract but might be in the body is what power these folks were at. Can you help us out with that answer?[/reply]I was able to get a copy of the whole article from my local university:

Foss Ø, Hallén J. Cadence and performance in elite cyclists. Eur. J. Appl. Physiol. 2005;93(4):453-462.
I will read it and try to report.

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Giovanni Ciriani
http://www.GlobusSHT.com

That would be true, if the total kinetic and potential energy of the system remained constant. In this instance it does not. So, the movement of the thigh cannot be analyzed as a pendulum (where the total energy of the system is constant less friction losses) even though it might superficially resemble one. So, if the energy of the parts is not kept constant when energy is lost it must be either lost as work or lost as heat. While I will agree that some is converted into work (see below) I submit that most is lost as heat. Unless you can show that the loss of energy in the thighs is totally accounted for by transfer to other elements in the leg (or to the bicycle as work) your analysis is wrong.
Well, that would all be cool if only the forces decelerating the thigh were tangential to the circle (in the direction of motion). They are not, AFAIK, so all that effort cannot be recovered as work but is, rather, lost as heat. Unless, of course, you can show me some work to demonstrate this is not the case.
Yes, but because the masses are substantially different but the speeds are much the same it is not possible to convert all of the energy contained in the thighs at maximum speed to the lower leg (which is moving up at the same time at pretty much the same speed). Unless, of course, you can show me some math that demonstrates it is possible. I look forward to seeing that. The problem with your simplistic analysis is you are ignoring the different masses and different motions (the lower leg is much closer to a circle, like the foot so the total energy variation of the lower leg is fairly small both because of the smaller mass of this element and the elliptical nature of the motion) of the different elements.
I would agree. The feet and shoes act pretty much as a spinning disk or rod.
I disagree, see above. Show me the math that proves your point.
Yes, but you can change the direction of the push to be either more or less tangential to the pedal circle. You would agree, I presume, that forces directed non-tangentially are "wasted". So, while it doesn't take much more than a "basic level" of coordination to make the pedals go around (3 yo's do it quite nicely) it seems to me that there is lots of room for efficiency improvement.
Yes, that is part of the problem. It is very difficult to correct the muscle force direction inefficiencies if these inefficiencies are masked by overwhelming forces coming from the other side.
If you would actually sit down and do the energy calculations you will see that the energy requirements to make the pedals go around one revolution with zero outside work being done vary with the square of the cadence, making the power losses vary with the cube of the cadence.
It is very clear to me, I have done all this work. You ought to try it rather than your thought experiment.

And, of course, you have the problem of explaining all those studies that show overall cycling efficiency varies with cadence, especially the part where efficiency starts to drop above a "most efficient" cadence.

And, then there is this other way of looking at the issue. The efficiency of the contracting muscle is about 40%. The overall efficiency of most cyclists at the wheel is about 20%. You can account for 1-2% of that difference through drive train losses. Account for all of these losses. I look forward to seeing how you do it without invoking pedaling motion losses.

edit: however the problem is analyzed one should come up with the same asnwer if the analysis is done correctly.

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Frank,
An original Ironman and the Inventor of PowerCranks

Interesting thread. I stopped reading here, though.

I stand corrected...

Wow.

Rather than sitting here and simply pontificating as to either how smart you are or how dumb I am why don't you (or Tom, or anyone else) actually do some of the work and show me (and everyone else) where my comments above are wrong? I will wait patiently.

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Frank,
An original Ironman and the Inventor of PowerCranks

... snip ...

Read this out loud:
Those two groups of forces are independent and superimposed

Mechanical forces:
Yes, there is a metabolic cost to have to apply the forces fast (and maybe precise in time, depending on technique) with a high cadence/pedal velocity.

No, there is (virtually) no metabolic cost to continually stop and accelerate the limbs in a pendulum or circular way.[/reply] That would be true, if the total kinetic and potential energy of the system remained constant. In this instance it does not. So, the movement of the thigh cannot be analyzed as a pendulum (where the total energy of the system is constant less friction losses) even though it might superficially resemble one. So, if the energy of the parts is not kept constant when energy is lost it must be either lost as work or lost as heat. While I will agree that some is converted into work (see below) I submit that most is lost as heat. Unless you can show that the loss of energy in the thighs is totally accounted for by transfer to other elements in the leg (or to the bicycle as work) your analysis is wrong. I don't know where to start... You say that the total KE and PE does NOT remain constant. Everything you say after that pivotal statement is based on that statement. If you are wrong you need to rethink, right? Everyone that has uttered an opinion in the matter says/thinks/knows you are wrong. We (that excludes you) all know that there is a constant giving and taking of KE and PE between limbs, rotational parts and "vehicle KE".
Is it the "human flesh" aspect that bothers you? What if the "cyclist" had metal parts for legs with frictionless joints. Put that cyclist on a fixed and let him roll down a hill. Would the metal parts in the "legs" heat up? Yes or no?
Depending on your answer we can move on or ... I don't know what ...

Cadence Minge is the name of an Australian doctor you know.

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He who understands the WHY, will understand the HOW.

That would be true, if the total kinetic and potential energy of the system remained constant. In this instance it does not. So, the movement of the thigh cannot be analyzed as a pendulum (where the total energy of the system is constant less friction losses) even though it might superficially resemble one. So, if the energy of the parts is not kept constant when energy is lost it must be either lost as work or lost as heat. While I will agree that some is converted into work (see below) I submit that most is lost as heat. Unless you can show that the loss of energy in the thighs is totally accounted for by transfer to other elements in the leg (or to the bicycle as work) your analysis is wrong. I don't know where to start... You say that the total KE and PE does NOT remain constant. Everything you say after that pivotal statement is based on that statement. If you are wrong you need to rethink, right? Everyone that has uttered an opinion in the matter says/thinks/knows you are wrong. We (that excludes you) all know that there is a constant giving and taking of KE and PE between limbs, rotational parts and "vehicle KE".
Is it the "human flesh" aspect that bothers you? What if the "cyclist" had metal parts for legs with frictionless joints. Put that cyclist on a fixed and let him roll down a hill. Would the metal parts in the "legs" heat up? Yes or no?
Depending on your answer we can move on or ... I don't know what ... [/reply] Well, lets just look just at the thighs, the part that looks like a pendulum. One thigh is going up and the other thigh is going down so the total PE for that part of the system should remain constant, shouldn't it. But, during this time, the thighs are accelerating and decelerating from zero speed to maximum speed and back and both are at maximum or minimum at the same time. The total of the energy of that part of the system cannot be constant even though it looks like a pendulum it does not behave like one.

I don't care what these other people are saying because what they are saying is utter nonsense. Do the math. Show me where this "constant giving and taking of the energy is occurring between the limbs. This could only occur if the energy of the system is constant. Since it is not then energy must constantly be put into the system to make up for that which is lost. If you can show that all of the energy that is lost is used to drive the bike then that would be cool but, then, how do you explain the efficiency difference between the muscle and the cyclist overall?

It is not the human flesh part of the problem that bothers me. The physics is the same. Put your metal cyclist with zero mass wheels on a sloped ramp and watch him speed up. Does he speed up as fast as a frictionless disk of equal total mass sliding down a similar slope? I think not. And, the more mass in those thighs (the biggest contributor to this problem) the slower he will accelerate. That means there is an energy cost to the motion and, yes, the legs would warm up (they have to as the energy has to be lost as heat) just as the connecting rods in an automobile engine will warm up (and even break if the engine revs fast enough) from these forces or as a spoon or wire warms up if you flex it back and forth.

Or, take your metal man and take his feet off the pedals and spin them to x rpm and see how long it takes to spin down. Then attach his feet to the pedal and spin them again to the same rpm and see if the spin down time is the same. If it is not, there is an energy cost to pedaling beyond the frictional cost. Simple as that.

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Frank,
An original Ironman and the Inventor of PowerCranks

...snip...

It is not the human flesh part of the problem that bothers me. The physics is the same. Put your metal cyclist with zero mass wheels on a sloped ramp and watch him speed up. Does he speed up as fast as a frictionless disk of equal total mass sliding down a similar slope? I think not. And, the more mass in those thighs (the biggest contributor to this problem) the slower he will accelerate. That means there is an energy cost to the motion and, yes, the legs would warm up (they have to as the energy has to be lost as heat) just as the connecting rods in an automobile engine will warm up (and even break if the engine revs fast enough) from these forces or as a spoon or wire warms up if you flex it back and forth. .. snip ...

Ok, now I see you level of understanding. Do you realize that what you claim here has Nobel prize proportions? Simply rocking/shaking a pair of metal "thighs" would make them heat up?
Frank, this is futile. You can't picture or understand the dynamics of KE in a system of levers, rockers, rotations and translation. Yet you claim what the consequences of your (mis)understanding must lead to heat generation, in direct violation of all experience.
BTW1: connecting rods in combustion engines heats up from combustion heat, do you account for that and claim they heat up even more from the oscillations?
BTW2: bending a spoon or wire back and forth will generate heat if you stress the material to the point of inelastic yield. Irreversible deformation work is being done and heats the metal. Not related at all to what we are discussing.
BTW3: I put out my highest 20-40min power at ~76rpm with my 165mm cranks, FWIW.

There cadences are right, for the cycling world. Triathlon is a bit different. Triathletes don't quite train as much on the bike, don't put out quite as much power output, and have to run afterwards. Which leads to the wise choice of lower cadence for our sport, and even lower for an Ironman versus a sprint tri.

well, I guess our understanding of materials science is simply different. I was not aware that any perfect materials actually existed, materials that have no internal friction/resistance and are perfectly stiff. Apparently I was under the, according to you, misapprehension that friction caused heat which somehow caused me to believe that stressing any real object in any way would cause a temperature change, albeit usually small. But, not always small. For instance, I was not aware that the average tire is routinely stressed beyond the point of "inelastic yield" yet it seems they seem to heat up substantially when in normal use. I always attributed that to internal friction, but, maybe I am imagining that.

Anyhow, the fact remains that the energy efficiency of a contracting muscle is about 40% and the energy efficiency of the average cyclist is about 20%. That efficiency difference is being lost as heat somewhere between the muscle and wheel. You have yet to explain to me and the rest of the peanut gallery here where that loss is occurring. I am still waiting for that explanation professor.

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Frank,
An original Ironman and the Inventor of PowerCranks

What wasn't in the abstract but might be in the body is what power these folks were at. Can you help us out with that answer?

If they were at 400 watts it would suggest to me that even if 80 rpm was optimum for these folks that those who ride at substantially lower power (and for substantially longer times) would be much better off at substantially lower cadences.[/reply]Sorry it took a while. I quote from the study: Foss Ø, Hallén J. Cadence and performance in elite cyclists. Eur. J. Appl. Physiol. 2005;93(4):453-462.


"In the present study, the cyclists performed a time trial of about 28 min at self-selected and variable power with the goal to complete a given work as fast as possible. The average workloads ranged from 312 to 351 W (60–120 rpm, Table3)."


What's most interesting is a key conclusion, stated in the study, which I quote below:


"The optimal cadence found in the present study (80 rpm) is lower than the cadence normally preferred by cyclists (90–105 rpm). Are cyclists using a cadence that is too high? Professional cyclists generally have a higher V_ O2max and are able to utilise a higher fraction of V_ O2max than elite cyclists (Lucia et al. 1998, 2001;Padilla et al. 1999, 2000; Table 4) (Lucia et al. 1998,2001; Padilla et al. 1999, 2000). This enables them to work with a higher power output (Watts per kilogram) than amateurs and to sustain an external workload in the range of 400–500 W throughout 1-h events (Padilla et al. 2000; Mujika and Padilla 2001). Based on the finding that the most efficient cadence increases with increasing workload, one cannot exclude the idea that professional cyclists are more efficient at cadences even higher than 80 rpm. Lucia et al. (2004) examined the effect of cadence on efficiency in professional cyclists. Ata mean (SD) external workload of 366 (37) W, gross efficiency was higher at 100 compared to 60 rpm, but was not statistically different from 80 rpm. It is our experience that amateur cyclists often adopt their cadence from professionals in the belief that professionals have an optimal cadence. This could be wrong since the most efficient cadence changes with workload."

I have uploaded the study in my web site. If any body is interested, e-mail me and I will e-mail back a copy, if it is only for personal reading.

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Giovanni Ciriani
http://www.GlobusSHT.com

Thanks for that. I look forward to reading the entire study. As I noted in my PM to you this must really be a great study because it supports what I have believed for a long time.

From the point of view of this thread these folks are putting out substantially more wattage than even the male pro triathletes yet their optimum cadence is less than what Dan suggests "all" the pros have converged upon. Suggests to me that ought to consider reducing their cadence some and that, perhaps, even Chrissie is still a little higher than would be her optimum, as I suppose her power is substantially lower than the pro men..

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Frank,
An original Ironman and the Inventor of PowerCranks

you all don't get it...
brett sutton is a triathlon coach... he doesn't care about swimmers, cyclists or runners.
read his stuff on the team forum.
riding over 90rpm kills the run. he even states every athlete is different. some ride in 80's some ride in the 70's.
running cadence is over 90 for the athletes.

siri does the same for her athlete's (i'm one of them)
mirinda was running over 100+ on some treddy sessions. it's nueromuscluar training.
chrissie's running cadence is also high 90's. which is needed for ironman marathoning. cw has posted 7 out 8 sub 3:03 marathon splits except for korea. no female or male pro can say that.

keep it simple and stop comparing apples to oranges

I know I am late to the thread. Has Chrissies cadence changed over the last 3 years?

If not, then perhaps something else can explain her last 15 miles. Like pushing to hard and/or nutrition.

If her cadence is different than her first 2 wins, than maybe you have a point?

riding over 90rpm kills the run.

Perhaps for some. Don't tell Craig Alexander that. He rides at over 90 pretty much all the time, and significantly higher than all the rest of the men.I even saw him, god forbid, shift to the small ring a few times last weekend at IMH going up some of the hills.

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Steve Fleck @stevefleck | Blog