Another try at the "Biomechanical Evaluation of Pedalling Mechanics-Big Lance' thread

[alienator]

No spring action but there is a benefit. What you are doing is increasing the potential energy of that leg which is returned on the downstroke. So, getting the leg up does not do work directly but it does do work indirectly. So, the question then becomes, which is the most efficient or best way to do that work, using the muscles of that leg to do the work directly, using the muscles of the other leg to do the work indirectly, or some combination.

A very small amount of potential energy, decreased further by mechanical losses in the drivetrain and on the road surface, as well as by any opposing forces generated by muscle movement. I'm willing to bet the amount of potential energy is so small that it essentially doesn't matter.

 

[dhk2]

No spring action but there is a benefit. What you are doing is increasing the potential energy of that leg which is returned on the downstroke. So, getting the leg up does not do work directly but it does do work indirectly. So, the question then becomes, which is the most efficient or best way to do that work, using the muscles of that leg to do the work directly, using the muscles of the other leg to do the work indirectly, or some combination.

Agree work is being done to raise the back leg, and that either leg in theory could do the work, but it's not being done with muscle power alone. Since the legs are essentially the same weight for most of us, the weight of the falling leg will balance the weight of the rising leg; ie, the falling leg lifts the back leg without any need for additional energy input at all. Potential energy is exchanged between the legs as we pedal, but not lost. In fact, it could be said that conventional cranks lift the back leg "for free" by using the weight of the front falling leg.

Your statement is still valid when it comes to maintaining a certain level of net torque output from the crank. But if merely lifting the back leg was the issue, that's easily done by the weight of the falling leg (once the cranks are in motion at a constant cadence) without any significant muscle input needed from either leg.

 

[Fday]

A very small amount of potential energy, decreased further by mechanical losses in the drivetrain and on the road surface, as well as by any opposing forces generated by muscle movement. I'm willing to bet the amount of potential energy is so small that it essentially doesn't matter.

I'll bet if you were to actually do the math you wouldn't be quite so willing to "bet" this is "so small that it essentially doesn't matter." Let's simplify this and just talk about just the thigh. Assume the average thigh weighs about 25 lbs and its center of mass is located in its middle, such that the CM of the thigh moves up half the distance the pedal moves up when going from BDC to TDC. If the crank length is 6 inches then the thigh CM moves up 6 inches. At a cadence of 60 each thigh will move up once each second, meaning that about 12.5 ft-lbs/second work has been done. 1 ft-lb/sec equals 1.36 watts. Add in the lower leg and foot and increase the cadence and you are starting to talk about numbers that could make a cycling difference don't you think?

 

[alienator]

I'll bet if you were to actually do the math you wouldn't be quite so willing to "bet" this is "so small that it essentially doesn't matter." Let's simplify this and just talk about just the thigh. Assume the average thigh weighs about 25 lbs and its center of mass is located in its middle, such that the CM of the thigh moves up half the distance the pedal moves up when going from BDC to TDC. If the crank length is 6 inches then the thigh CM moves up 6 inches. At a cadence of 60 each thigh will move up once each second, meaning that about 12.5 ft-lbs/second work has been done. 1 ft-lb/sec equals 1.36 watts. Add in the lower leg and foot and increase the cadence and you are starting to talk about numbers that could make a cycling difference don't you think?

You skip right over the kinetic energy of the falling opposite leg offsetting the great majority of that potential energy increase. The increase in potential energy cannot be considered independent of the expenditure of kinetic energy in the falling leg. It'd be convenient to be able to decouple a system like that, but it can't be done.

Thanks for being flip, though, about the math. It really gives you credibility.

 

[roadhouse]

alls i wanna say is you send me some powercranks and i'll put them to the test for the Ironman, Frank. i'm about to get started riding again and i'm gonna haul ass. let me know.

 

[Fday]

You skip right over the kinetic energy of the falling opposite leg offsetting the great majority of that potential energy increase. The increase in potential energy cannot be considered independent of the expenditure of kinetic energy in the falling leg. It'd be convenient to be able to decouple a system like that, but it can't be done.

Thanks for being flip, though, about the math. It really gives you credibility.

Hey, the math is the math. If you want to use the energy in the other leg to get back leg up, fine. It seems to me, though, that it would be better to use that energy you have put into that rising leg to actually drive the bicycle, if possible. The energy to get the let up has to come from somewhere. It is either going to rob from the energy available to drive the bicycle or it is not.

And, I am glad you think it would be nice to be able to decouple such a system (even though you think it can't be done) because that is exactly what PowerCranks do. With PowerCranks it is impossible to use the energy in the falling leg to assist (put energy into) the rising leg.

 

[alienator]

Hey, the math is the math. If you want to use the energy in the other leg to get back leg up, fine. It seems to me, though, that it would be better to use that energy you have put into that rising leg to actually drive the bicycle, if possible. The energy to get the let up has to come from somewhere. It is either going to rob from the energy available to drive the bicycle or it is not.

And, I am glad you think it would be nice to be able to decouple such a system (even though you think it can't be done) because that is exactly what PowerCranks do. With PowerCranks it is impossible to use the energy in the falling leg to assist (put energy into) the rising leg.

Actually you completely misread what I intended re: decoupling the system. I meant that you cannot decouple one half of a traditional cranks system from the other half in the mathematical analysis. What you'd "like" to do with the kinetic energy from the falling leg in a crankset really doesn't matter. The simple fact is part of the energy imparted to a falling crank arm is converted to potential energy in the rising crank arm. When one leg goes down, the other leg can't help but go up. It's part of that whole rigid structure thing with cranksets.

It is cute, if not smarmy, that you use the opportunity to pimp your system.

Pimp your system all day long, but at the end of the day, you're going to have one hell of time decoupling the dynamics of one half of a quasi-rigid crankset from the other.

 

[Fday]

Actually you completely misread what I intended re: decoupling the system. I meant that you cannot decouple one half of a traditional cranks system from the other half in the mathematical analysis. What you'd "like" to do with the kinetic energy from the falling leg in a crankset really doesn't matter. The simple fact is part of the energy imparted to a falling crank arm is converted to potential energy in the rising crank arm. When one leg goes down, the other leg can't help but go up. It's part of that whole rigid structure thing with cranksets.

It is cute, if not smarmy, that you use the opportunity to pimp your system.

Pimp your system all day long, but at the end of the day, you're going to have one hell of time decoupling the dynamics of one half of a quasi-rigid crankset from the other.

Well, if you want to look at the kinetic energy of the legs it is the math that decouples them since the kinetic energy of both thighs increase and decrease at approximately the same time as they are both at minimum speed and maximum speed at about the same time. Therefore, it is not possible to transfer anything from one to the other so they are, effectively, decoupled from a kinetic energy perspective.

Coupling is only "complete" if the energy transfer is complete and done in such a fashion as to allow the total energy of the system to remain constant. That never happens when riding a bicycle.

That coupling issue, however, is a completely different issue than the potential energy coupling question I was referring to. I agree, it is possible to use the PE in the leg at the top to get the other leg to the top. However, doing so doesn't allow one to use that energy to propel the bicycle. If you don't care about that loss so be it. Those who are interested in making their bike go fast seem to care. It was one of the points made in the referenced article, one should try to minimize the negative forces on the upstroke. You are, of course, free to believe differently if you care to.

 

[n crowley]

Well, if you want to look at the kinetic energy of the legs it is the math that decouples them since the kinetic energy of both thighs increase and decrease at approximately the same time as they are both at minimum speed and maximum speed at about the same time. Therefore, it is not possible to transfer anything from one to the other so they are, effectively, decoupled from a kinetic energy perspective.

Coupling is only "complete" if the energy transfer is complete and done in such a fashion as to allow the total energy of the system to remain constant. That never happens when riding a bicycle.

That coupling issue, however, is a completely different issue than the potential energy coupling question I was referring to. I agree, it is possible to use the PE in the leg at the top to get the other leg to the top. However, doing so doesn't allow one to use that energy to propel the bicycle. If you don't care about that loss so be it. Those who are interested in making their bike go fast seem to care. It was one of the points made in the referenced article, one should try to minimize the negative forces on the upstroke. You are, of course, free to believe differently if you care to.

Unweighting requires no more effort than raising your leg off the ground when walking or running, if done when using standard cranks it does increase power on the downward leg but if done by means of PC's, power is reduced in that downward leg. Here is the explanation: if you remove the chain from the chainring and set standard cranks spinning, they will continue to rotate indefinitely. When pedalling, independent PC cranks turn this simple effortless rotating action of the cranks into a difficult task that leads to severe hip flexor pain and a sore rear end because most of the additional force that should be going to the downward leg is going to the saddle and your concentration on power application by that downward leg is distracted by that unavoidable PC crank lifting operation.

 

[swampy1970]

Clipless pedals are ok for you, but then you are not applying maximal torque as your pedals pass through 12 o'c.

I highly doubt that even JA was applying max torque at TDC.

It's easy to make vague statements and 38% power increase claims, explain how the pedalling objectives of a PC'er differ from those of a circular pedaller.

What is a circular pedaller - there is no such thing. There's a person who believes the apply equal power, or at least equal effort but the only think they're really doing with regards to that is fooling themselves and pedalling much like the rest of us.

38% power increase wasn't a 'claim'. It was measured and the resulting measurement verified in training. It's only a claim if you can't back it up with hard, reproducable numbers.

There was nothing vague about my statements...

There's still lots of work to do... If anything the biggest thing isn't just the way I changed my pedalling but the resulting "redistribution of effort". The quads and glutes don't tire as fast as the quads.

Explain what muscles PC's train and where exactly in the pedalling circle the resultant power increase from this training becomes obvious to the PC user.

I could tell you what hurts the most but the fact is that we can believe that "muscle x" is doing a certain task but the simple fact is that we (at least I) can't concentrate on two things at once so trying to keep track of what both legs are doing at the same time.

Since the PC's force you to bring the cranks up, you no longer have to think about that part of the pedal cycle so you can think about getting the pedal across the top and using the hamstrings and glutes to hammer things home on the way down - which was my big thing, cause when I used to race those muscles were always pretty fresh at the end of an event and my quads were f*#ked.

Did you ever consider perfecting the unweighting/mashing technique for comparison purposes.

I don't think anyone knows what the perfect "unweighting/mashing technique" is. I'd go as far as saying that I don't think that anyone knows what the perfect pedalling technique is...

... all I can tell is that my power has increased more at a greater rate during my period of PC use than at any time - even when I was pretty much devoting my life to racing over a decade ago. I can develop more power now for an hour than I could back then too...

 

[swampy1970]

Unweighting requires no more effort than raising your leg off the ground when walking or running...

Yes it does... Do you ever walk with your torso about 0 to 20 degrees from the horizontal? If you do can I start calling you drunken monkey man?

Likewise, if you're on a bike with PC's, riding no handed makes pedalling much easier when you're getting started.

 

[Fday]

Yes it does... Do you ever walk with your torso about 0 to 20 degrees from the horizontal? If you do can I start calling you drunken monkey man?

Likewise, if you're on a bike with PC's, riding no handed makes pedalling much easier when you're getting started.

Further, when one is walking one doesn't normally lift the foot 14 inches off the ground each step, which is what is required to get the crank around the circle when riding 7 inch cranks. To lift it 14 inches off the ground when bent over is an even more difficult task, when done 90 times a minute for hours on end.

 

[roadhouse]

Well, if you want to look at the kinetic energy of the legs it is the math that decouples them since the kinetic energy of both thighs increase and decrease at approximately the same time as they are both at minimum speed and maximum speed at about the same time. Therefore, it is not possible to transfer anything from one to the other so they are, effectively, decoupled from a kinetic energy perspective.

Coupling is only "complete" if the energy transfer is complete and done in such a fashion as to allow the total energy of the system to remain constant. That never happens when riding a bicycle.

That coupling issue, however, is a completely different issue than the potential energy coupling question I was referring to. I agree, it is possible to use the PE in the leg at the top to get the other leg to the top. However, doing so doesn't allow one to use that energy to propel the bicycle. If you don't care about that loss so be it. Those who are interested in making their bike go fast seem to care. It was one of the points made in the referenced article, one should try to minimize the negative forces on the upstroke. You are, of course, free to believe differently if you care to.

damn them real cyclists...

 

[n crowley]

Further, when one is walking one doesn't normally lift the foot 14 inches off the ground each step, which is what is required to get the crank around the circle when riding 7 inch cranks. To lift it 14 inches off the ground when bent over is an even more difficult task, when done 90 times a minute for hours on end.

Get yourself standard cranks and someone to teach you the most effective unweighting technique which uses only a correctly timed raising of the knee and momentum of the fast moving lower leg/pedal/crank, then you will discover the error of your PC ways.

 

[tessitori]

. Here is the explanation: if you remove the chain from the chainring and set standard cranks spinning, they will continue to rotate indefinitely.

I will try doing this on my bike after dinner! I doubt they will even spin for 2 minutes! Does this happen only with ceramic bearings that they can spin indefinitely? I must upgrade to whichever cranks you are using .

 

[n crowley]

I know it is hard for you to understand but what was described in the armstrong article is exactly what the PowerCranks force the rider to do.

Does this mean Armstrong had to endure the same pain as that experienced by all PC users when they begin to use the PC style of pedalling ?

 

[roadhouse]

pain usually means that you were not completely doing it right to begin with (optimal use of muscles were not taking place) and that there were muscles not in use to begin with or not in that much use and were weak and needed refining and if after the fact there is no pain and power output increases along with speed then something is right with it. pain can be overcome and if it's only in the beginning then that'd be the oddball and stationary way to call these powercranks out, IMO.

now if one needed knee replacement surgery after the fact then that's another story entirely but Lance didn't, he just got faster, again.

i've never used anything other than regular cranks but pain is usually aligned with muscles being weak is all i'm really trying to get at but i'm not a doctor like Frank is but since day one of riding bikes, i've known that pulling up and dead spots were entirely unique in their need for development for sustaining an easier cadence, smoother and less fractioned pedal. whether or not Powercranks deliver, i can't really say but i've seen enough testimonials on them to raise an eyebrow and we're not talking just your weekend warriors either, not that PC's haven't seemingly helped them out plenty as well though.

not sure i should hit the submit button as i'm not sure i really want to get bashed upside the head for my neanderthal-ish repy that might could only make sense to myself but what the hey, here goes...have mercy!

 

[Enriss]

Your post makes a lot of sense to me.

 

[roadhouse]

good, then this will as well. cycling and pain go hand in hand, especially for those who care to go fast and no when else does it hurt morso than in the beginning, right or wrong? cheezy attack by crownie on the PC's to begin with. in the beginning you were too slow and are now currently in need of Power Cranks or at the very least the need to bash them. Mr. Crowely Sir, have you yourself used Power Cranks? it will make all the world in the differnce as to your argument, if you care one way or another that is.

 

[n crowley]

If anything the biggest thing isn't just the way I changed my pedalling but the resulting "redistribution of effort". The quads and glutes don't tire as fast as the quads.
Since the PC's force you to bring the cranks up, you no longer have to think about that part of the pedal cycle so you can think about getting the pedal across the top and using the hamstrings and glutes to hammer things home on the way down - which was my big thing, cause when I used to race those muscles were always pretty fresh at the end of an event and my quads were f*#ked.

In your estimation what percentage of 3 o'c torque are you applying across the top at 12 o'c (excluding momentum of the leg at 12). You don't mention across the bottom. I am well aware that the glutes and quads don't tire as fast as the quads. Correctly used the glutes are capable of applying even greater crank torque across the top at 12 than the quads can apply at 3 o'c, and it is the successful merging or combination of these powerful muscles that leads to 180 deg. of continuous almost max torque application with each leg in the less tiring linear style of pedalling. Frank believes the PC advantage lies in the "across the bottom", upstroke and "across the top" areas of the pedalling circle, you appear to believe it lies in the downstroke.