It is the nature of a friction loss (and viscous loss is generally a friction loss). Once the coeeficient of friction is known a friction loss is only dependent upon the speed. An energy loss (the material deformation loss) is generally dependent upon the speed squared. Here is the curve I was referring to. I think it is evident that the slope is tending to increase as the data moves to the right.


It is why it takes a longer distance to stop when one is going faster whether it is a bike, car, or train. It is why rolling resistance forces don't change the same as wind resistance forces.

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Frank,
An original Ironman and the Inventor of PowerCranks

Frank,
A friction loss (loss measured in watts) should be F*V, in which F is the friction force and V is speeds, so if F is constant the loss should increase linearly with the speed (cadence). However, if the friction is caused by some internal pressure in the muscle fibers that changes with speed than there would be a non-linear component. Also if tendon and sarcomere elasticity intervene, such elasticity would decrease the sliding path of myo-filaments, thereby decreasing the total power lost. As a result I would imagine the friction loss would be less than linear, i.e. as you increase cadence the power lost by friction increases less than linearly (for instance proportional to the square root of speed or to some exponent less than 1).

Viscous forces are different from friction forces, and are in general approximated by a constant * V. Therefore, the power lost for viscosity (force * V) would be proportional to the square of V.

These are wild guesses, as I do not have the foggiest idea of what muscle physiology research has discovered, and I stand to be corrected by somebody else (dr. Coggan?).

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Giovanni Ciriani
http://www.GlobusSHT.com

Well, friction loss is defined in a certain way. If you want to define another type of loss that is non-linear and not dependent upon energy absorbtion then I think you need to come up with a mechanism for it and define it (and find some experimental evidence to support that it exists). If you are right then a third term must be added to the model.

Part of the problem here is most of the so-called scientists who "study" this stuff (some of them hang out here) have come to think (after analysis of the perfect MMF model) that there are no significant losses to be found here so it is pretty much ignored (and anyone who does try to bring it up will be hooted out of the auditorium).

edit: I thought viscous forces depends upon the fluid. It was my understanding that in the body and at body speeds that viscous forces behave as friction forces (except, perhaps in the joints where they behave as lubricants with very low losses).

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Frank,
An original Ironman and the Inventor of PowerCranks

I believe a lot of this work has already been done. It just hasn't been done by (or, noticed by) exercise scientists. This knowledge is important in forensics in trying to reconstruct accidents. If X bone is broken is an certain way then it is known that at least Y amount of energy was applied. A simple google search for energy absorbtion characteristics of muscle and bone found this:


While this document doesn't seem to address all of the issues I have brought up it does show that biologic tissue does deform and does absorb energy, the points I was originally trying to make. Further, it makes the point that soft tissue can absorb substantially more energy than bone. This, of course, will make it much more difficult to model.

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Frank,
An original Ironman and the Inventor of PowerCranks

Frank,
I think everybody here agrees with that statement. Muscle when loaded eccentrically absorbs energy. I believe though, you gave the impression to everybody else that muscle was absorbing a good deal of energy when not loaded eccentrically, and just because it was pedaling unloaded.

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Giovanni Ciriani
http://www.GlobusSHT.com

You have to be careful with your problem here. If you think of bones and muscles as springs, the bone is a stiff spring and the muscle a soft spring. In a pure stretch of a spring, the force in the spring is F=k*x (x=amount of stretch). The strain energy is U=.5*k*x^2. I think you would agree that the muscles are in parallel with the bones except at the joints (in which case the muscle system would act primarily as a torsion spring). For springs in parallel, the forces and strain energy would be

1) keq=k_bone+k_spring
2) x=F/keq
3) F_bone=k_bone*x, F_muscle=k_muscle*x
4) U_bone=k_bone*x^2/2, U_muscle=k_muscle*x^2/2

As k_bone>>k_muscle, the force transmitted through and strain energy of the bone is much higher than that of muscle.

I expect the "attenuation" in the quoted text is due to eccentric loading causing a moment to be reacted through the joints. Those "soft spring" muscles are deforming over a large angle.

From a damping perspective, all the tissue around bones wouldn't do much in my opinion for loads transmitted along the length of the bone. In the radial direction you'd expect quite a bit of attenuation as the load path is "soft" (through that skin, muscle, and fat) until it his the bone. A soft spring and damper. But along the length of the bone that tissue won't do much if the load introduction is at one end of the bone.

Think of a vibration isolator. Typically they are rubber with 2 metallic interfaces that are not connected. Why aren't they connected? Because it they were you've introduced a stiff load path and bypassed that soft, "energy absorbing" path. See http://www.vibrationmounts.com/Products1.htm and click on the products to see the part schematics.

Well, we don't know that energy isn't lost into tissue just from shaking it. It should occur but I don't have a number. How much heat is lost from shaking a water balloon? If we knew that we might have a clue what is going on in the thigh simply from this passive loss. What we know is that energy is being absorbed to account for the losses. It could be being absorbed in many different ways, all adding up to the whole. Perhaps muscle contracts when it senses stretching occurring from a sideways force/distortion (the stretch reflex is a natural reflex) whch would cost energy but not be an eccentric contraction. Is that a "material distortion" loss in the traditional sense? No. But, it certainly would be an energy cost that is not a traditional contraction in the concentric or eccentric sense. Who knows, what is going on? The losses are there. The so-called "exercise scientists" here have chosen to invent reasons to ignore them rather than investigate them. And, then they choose to call those who are curious about them stupid.

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Frank,
An original Ironman and the Inventor of PowerCranks

Frank,
Here we go again. The book excerpt you posted says that muscle absorbs energy in an excentric contraction. Perhaps they don't use the word excentric, but then they make the example of landing from a jump, which is an excentric absorption of energy. In a pedaling effort most of the energy is developed concentrically in the descending pedal, and only a tiny fraction is absorbed excentrically in the ascending pedal. I think the diagram posted by Andrew Coggan evidenced that pretty well.

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Giovanni Ciriani
http://www.GlobusSHT.com

I am not aware of any skeletal muscles that don't go across a joint except, perhaps, the eye and facial muscles and the tongue.

Regarding the vibration isolator, even if you introduce a stiff member into the equation, the same amount of energy has to be absorbed. It will simply be absorbed differently.

The body is more than just bones and muscles. Is is also a big fat water balloon. Me thinks the dynamics here as to what is going on could get very complicated. The fact that it is complicated isn't a particularly good reason to simplify the problem to the point of eliminating all the losses, which makes the problem pretty simple. Only problem is you assure your answers are going to be wrong. But, what do people care? As long as it sounds right and good, correct?

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Frank,
An original Ironman and the Inventor of PowerCranks

I stated in my post that the book did not address all of the issues I was talking about. I simply pointed to it as an example that the tissues of the body have the ability to absorb energy in both active and passive ways.

I am not sure what Coggans diagram has to do with this argument. If one simply looks at the thigh, the energy put in to accelerate it is essentially the same whether it is moving up or moving down. And, the energy being put in is pretty much perpendicular to the bone and muscle directions (at least for the muscles in the leg). If the energy of the system is to remain constant (to avoid violating the 1st law) then excess energy must be either stored and then returned or totally lost. To keep the system going then, when the energy is naturally decreasing additional energy must be put in to keep it going. Without that additional energy the motion has to eventually stop. That is why the MMF cannot go on forever except in the single instance where losses are declared to be zero.

We can argue the magnitude of the losses and where they are occurring or anything else except we cannot argue whether they are actually there (except we have just finished a couple of days worth of posts doing just that - at least that seems to stop). Unfortunately, I am not aware of any data to tell us exactly how these losses happen. We know the losses are there (see the McDonald paper). Anyone who says they know for sure how the losses are distributed must be guessing (although it may be an educated guess, which is what I hope my guess is).

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Frank,
An original Ironman and the Inventor of PowerCranks

Then tendons, ligaments, etc. Remember, I'm a mechanical/aero engineer, not an anatomy expert!
Yes, but if your goal is attenuation, the response will be different. Those rubber isolators may give you 10% damping, which is significant. A metallic (or bone) rod will exhibit very minimal damping (less than 1%). If the goal is to attenuate or isolate, sticking a stiff member into the system is not the best idea. If you think of it in terms of a mass-spring-damper system, in one case (the stiff member) you'll oscillate for a long time. In the other case (rubber isolator) with the same initial conditions you'll damp out quickly. Same "energy" at the start, but completely different response.

It all depends on the direction/location of the loading. As a doctor you should know this very well. The old tap test on the knee to test those reflexes. Whack the bone and you get one form of wave propagation. Whack the thigh and it's completely different. The attenuation and propagation of the stress wave is directionally and materially dependent.

Even if the body is a big water balloon, if you load through the spine it will hurt like hell! Do a thought experiment. Take your water balloon that has a steel rod through it. Put a strain gage and accelerometer on the rod. Drop the balloon/rod from a given height such that the impact direction is along the axis of the rod. Now drop it from the same height so the rod is in the plane of the ground. Being the drop height is the same, the potential energy is equivalent. What can you say about the stress and acceleration of the rod in these 2 cases?

I am not sure what your point is. The leg isn't primarily designed to "attentuate" vibrations but, rather to transmit and absorb energy in a way that allows us to walk and run efficiently (I don't think cycling was part of the evolutionary process). It is what it is. We are trying to use it for another purpose and we will invoke some, perhaps, different ways from how it was "designed" to transmit and absorb energy. I am not sure that it is necessary to fully understand every joule and where it goes. If we can understand that the energy lost really does vary with the square of the cadence then it might allow us to develop better strategies of minimizing the loss and maximizing the output. If we find that the loss varies directly with the cadence then it is probably not possible to develop better strategies. I think the evidence suggests the energy loss varies with the square of the cadence (whatever the mechanism(s)). If so, Chrissie racing at the low cadences she does, in relation to her competition, could, in part, explain her dominance.

Instead, misunderstanding about the energy cost of pedaling pervades the belief of the cycling "scientists" out there because they have used a totally useless model to look at the issue and, as a result, we get threads like this one.
I can't say anything about those two different scenarios because I have not been trained in this area except I can say they will be different. That is what forensic accident analysis is all about though so there are people who could probably answer that question. Experiments have been performed like that to help reconstruct accidents from which there are no survivors. I remember my brother-in-law telling me something about this. He was a military radiologist and he would be asked to xray dead pilots. By the type of fractures that were seen they could make assumptions as to whether the feet were on the rudders or the hands were on the throttles, or other things, at the time of impact, to help them analyze the accident.

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Frank,
An original Ironman and the Inventor of PowerCranks

I might add, that the reason we are discussing where the energy goes is not because we know that it is important to know this, at least in this situation, but because I was asked to explain this when people were using the perfect MMF model as an example to show that energy loss wasn't allowed.

Before I was asked that question to prove my point I didn't think it was necessary for us to understand exactly how the energy was dissipated, only that there were these inefficiencies and that we could influence them. Now that I think that everyone accepts that there are energy losses here it might be important to know more about where the losses occur to help develop strategies to mimimize them or it might not. I believe it is most important to know that these losses are there and how changes in cadence, crank length, and, maybe, body position might affect them. Beyond that, I am not sure much is to be gained.

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Frank,
An original Ironman and the Inventor of PowerCranks

Frank,
Again the book is not an example of the body ability to absorb energy in a passive way.

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Giovanni Ciriani
http://www.GlobusSHT.com

Ugh, the bone absorbs energy in a passive way, I believe. That excerpt referred to both deflection of the bone and active contraction of muscles to absorb energy as I remember.

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Frank,
An original Ironman and the Inventor of PowerCranks

It's never stopped you before, why start now?

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Steve

http://www.PeaksCoachingGroup.com

Yeah but you belive that circular pedalling is more effective than mashing despite a ton of evidence to the contrary. We don't care what you believe, what can you show!

Back to cadence the study you have brought up determines an optimal cadence for elite athletes (not Professionals) on a wind trainer. Can you show any evidence that this optimal cadence would apply to road cycling, under various conditions (wind, heat, altitude, gradient), various abilities (sub elite, professional) and at different phases for an athlete (in a power phases vs a conditioning phase, after 5mins riding vs after 5 hours) or is efficiency and cadence specific to the conditions, person and where that person is at in a ride/season.

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Hamish Ferguson: Cycling Coach

Fergie,

I really am not sure the few people still following this thread want it to be expanded to include a "discussion" as to exactly what "proof" someone should need before one changes something or drag PowerCranks into the debate. After all this thread has made the ST top thirty as regards responses without hardly any mention of PowerCranks or circular pedaling. If we did that I am sure we would soon be well above 1000 posts. So, I am going to resist this temptation to engage you again and simply say "different strokes for different folks."

Thanks for reading.

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Frank,
An original Ironman and the Inventor of PowerCranks

Ignorance is bliss I guess.

You were quite keen to discuss that study on Cyclingforumsn and it's implications. I see it as a reinforcement of the specificity principle. Sure know what cadence to train elite athletes at if their test is on a wind trainer.

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Hamish Ferguson: Cycling Coach

Rather than rehash everything again why don't we just provide a link to that thread to which you refer. Be warned folks, there are over 1600 posts in that thread. Oh, and for you folks that want some PC power data there are actually a couple of people who have posted power files in this thread, as if Fergie could care. Anyhow, have "fun".

http://www.cyclingforums.com/...sh-up-push-down.html

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Frank,
An original Ironman and the Inventor of PowerCranks

I don't understand your reluctance to discuss a study on cadence and efficiency that you claim proves you have been right all along. I mean you raised the study in the first place, you wanted my thoughts on it, seeing there seem to be a few more knowledgeable chaps involved in this thread lets discuss it here.

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Hamish Ferguson: Cycling Coach

Haven't we been doing that for the last 500 posts or so. Hasn't the study in question come up here? Have you waded through this entire thread? Why don't you ask a specific question and I will see if I can answer it.

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Frank,
An original Ironman and the Inventor of PowerCranks

Chrissie herself speaks about her cadence:
"I love to push a big gear. It’s a misconception that you need to spin a smaller gear at a higher cadence on the bike. You don’t. Doing that actually raises your heart rate and makes you more tired, which doesn’t serve you very well in long distance racing. Cranking it down and pushing a bigger gear lets me lower my heart rate. It’s what feels natural to me and enables me to go the fastest I can go."
http://bicycling.com/...chrissie-wellington/