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Dr. Jeff Broker on pedaling
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From VeloNews.com report on the Cycling Science Symposium and Expo in Colorado(http://www.velonews.com/...rticles/11504.0.html):

"Opening the list of speakers Monday was Jeff Broker, Ph.D., former biomechanist for the U.S. Olympic Committee. Broker currently serves as an assistant professor in the biology department at the University of Colorado at Colorado Springs. Armed with years of pedal-force graphs obtained from ongoing studies of elite cyclists at the Olympic Training Center in Colorado Springs, Broker demonstrated an intimate understanding of how a rider produces power at this most critical contact point.

Broker separated out the gravitational and inertial components of a pedaling force diagram, so that one could really see exactly what was being produced and at what cost to the rider. Broker noted that most cycling coaches spend a great deal of effort trying to eliminate the downward forces at bottom dead center part of a pedal stroke. That effort, he explained, is essentially futile, since most of that downward force present there is non-muscular and takes virtually no energy. Offering an extreme example, Broker suggested that one could knock a rider out cold, clip him into the pedals, tape him down to the saddle and handlebars and crank up the pedals up to 90rpm. The result, he said, would show similar forces expended at the bottom of the pedal stroke.

Understanding those non-muscular effects could prevent a coach from engaging in a counter-productive effort of trying to encourage a rider to eliminate forces which actually come at no energy cost. Indeed, the effort to eliminate them can actually cost a rider energy and efficiency."
Last edited by: Andrew Coggan: Jan 24, 07 10:58
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Re: Dr. Jeff Broker on pedaling [Andrew Coggan] [ In reply to ]
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Wow, thanks! I wonder if Frank Day and Gary T. have seen this ...

____________________________________
Fatigue is biochemical, not biomechanical.
- Andrew Coggan, PhD
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Re: Dr. Jeff Broker on pedaling [rroof] [ In reply to ]
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[reply]
Wow, thanks! I wonder if Frank Day and Gary T. have seen this ...[/reply]

Ugh, I have been saying this all along. It is why those who say cyclists don't pull up on the backstroke and that "all" the propulsive power comes from pushing are wrong when one accounts for the effects of gravity.

Frank

--------------
Frank,
An original Ironman and the Inventor of PowerCranks
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Re: Dr. Jeff Broker on pedaling [Andrew Coggan] [ In reply to ]
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Quote:
many in the audience were taken aback by a water-bottle design from MIT graduate student, purportedly able to save 110 seconds over the course of a 40 kilometer time trial
okay but what about the 110-sec water bottle?
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Re: Dr. Jeff Broker on pedaling [Frank Day] [ In reply to ]
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Ugh, I have been saying this all along. It is why those who say cyclists don't pull up on the backstroke and that "all" the propulsive power comes from pushing are wrong when one accounts for the effects of gravity.
Frank[/reply]

What exactly have you been saying all along or what is J. Broker trying to say. From my understanding of it, Broker like Coyle does not believe in the unweighting technique.
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Re: Dr. Jeff Broker on pedaling [Andrew Coggan] [ In reply to ]
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In Reply To:
...Broker suggested that one could knock a rider out cold, clip him into the pedals, tape him down to the saddle and handlebars and crank up the pedals up to 90rpm...

Yeah, but would he share the video?
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Re: Dr. Jeff Broker on pedaling [perfection] [ In reply to ]
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[reply]
Ugh, I have been saying this all along. It is why those who say cyclists don't pull up on the backstroke and that "all" the propulsive power comes from pushing are wrong when one accounts for the effects of gravity.
Frank[./reply]

What exactly have you been saying all along or what is J. Broker trying to say. From my understanding of it, Broker like Coyle does not believe in the unweighting technique.[/reply]

I don't know what Broker thinks about unweighting. However, if he has done an analysis of pedal forces that includes both the effects of gravity and inertia he will come to the conclusion that everyone "unweights" on the backstroke, they only differ in the degree of the unweighting. Further, they will see that those "big" forces on the downstroke do not come all from muscle pushing but they are augmented by the weight of the leg (or more specifically from the return of the potential energy put into the leg on the backstroke).

It is not important whether they believe in this principle or not, the facts are, everyone does it because the physics pretty much require it. Like I said it is a matter of degree. All PowerCranks do is make the rider change from a 90% unweighter to a 100% unweighter.

Frank

--------------
Frank,
An original Ironman and the Inventor of PowerCranks
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Re: Dr. Jeff Broker on pedaling [Frank Day] [ In reply to ]
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I don't know what Broker thinks about unweighting. However, if he has done an analysis of pedal forces that includes both the effects of gravity and inertia he will come to the conclusion that everyone "unweights" on the backstroke, they only differ in the degree of the unweighting. Further, they will see that those "big" forces on the downstroke do not come all from muscle pushing but they are augmented by the weight of the leg (or more specifically from the return of the potential energy put into the leg on the backstroke).
It is not important whether they believe in this principle or not, the facts are, everyone does it because the physics pretty much require it. Like I said it is a matter of degree. All PowerCranks do is make the rider change from a 90% unweighter to a 100% unweighter.
Frank[/reply]

Does a PC user have his total leg weight on the pedal when it's in the 6 o'c position.
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Re: Dr. Jeff Broker on pedaling [perfection] [ In reply to ]
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[reply]
I don't know what Broker thinks about unweighting. However, if he has done an analysis of pedal forces that includes both the effects of gravity and inertia he will come to the conclusion that everyone "unweights" on the backstroke, they only differ in the degree of the unweighting. Further, they will see that those "big" forces on the downstroke do not come all from muscle pushing but they are augmented by the weight of the leg (or more specifically from the return of the potential energy put into the leg on the backstroke).
It is not important whether they believe in this principle or not, the facts are, everyone does it because the physics pretty much require it. Like I said it is a matter of degree. All PowerCranks do is make the rider change from a 90% unweighter to a 100% unweighter.
Frank[./reply]

Does a PC user have his total leg weight on the pedal when it's in the 6 o'c position.[/reply]

They do when they are coasting (resting) with both legs down, but I suspect they don't when they are riding because they have to be pulling back which means the hamstrings are activated and the reactive force would tend to push the knee up some, reducing the downward force due to the dead weight of the leg on the pedal at the 6 o'clock position. I suspect the same is true for most riders who are trying to scrap the poo off the shoe. In addition, the PC'er is probably anticipating the upstroke some which would also tend to unweight the pedal some.

Anyhow, the above is a big guess and we won't know for sure what is really going on until someone does pedal force analysis.

Frank

--------------
Frank,
An original Ironman and the Inventor of PowerCranks
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Re: Dr. Jeff Broker on pedaling [Andrew Coggan] [ In reply to ]
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were you there and if so could you comment on the cleat placement/orthotics portion of the lecture?

Also, so should we never think of "pedaling in circles" or conciously pulling up on the upstroke?

Thanks,
Dan
www.aiatriathlon.com

http://www.aiatriathlon.com
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Re: Dr. Jeff Broker on pedaling [dtreeps] [ In reply to ]
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[reply]

Also, so should we never think of "pedaling in circles" or conciously pulling up on the upstroke?

Thanks,
Dan
www.aiatriathlon.com [/reply]

This was my thought also but my guess is that "virtually no energy" really means enough energy that you should still spin. I thought another reason for spinning circles was to keep your legs more relaxed and thus using less energy.
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Re: Dr. Jeff Broker on pedaling [dtreeps] [ In reply to ]
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In Reply To:
were you there and if so could you comment on the cleat placement/orthotics portion of the lecture?
Sorry, I wasn't there. Based on the available research, however, I'd say that cleat placement has negligible impact on performance (vs. comfort/injury prevention).
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Re: Dr. Jeff Broker on pedaling [Andrew Coggan] [ In reply to ]
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How about a crank system that varies the torque requirements (in relation to a fluid constant cadence) throughout the pedal stroke?

More leverage available = more torque required to keep constant cadence

Less leverage available = less torque requirement to keep constant cadence
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Re: Dr. Jeff Broker on pedaling [dtreeps] [ In reply to ]
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The message here is that looking at the force vectors a cyclist produces on the pedals as it makes it's way round the circle can be misleading. If you look at these types of graphs, you'll see that the cyclist is "pushing" down significantly into the pedal at the 6 o clock position.

What the Dr. Broker is saying is that much of this is simply a resul of the weight of the cyclist's leg being forced to go in a circle. Nothing more.

What this has to do with pedaling circles I'm not sure.
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Re: Dr. Jeff Broker on pedaling [Kevin in MD] [ In reply to ]
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[reply]
The message here is that looking at the force vectors a cyclist produces on the pedals as it makes it's way round the circle can be misleading. If you look at these types of graphs, you'll see that the cyclist is "pushing" down significantly into the pedal at the 6 o clock position.

What the Dr. Broker is saying is that much of this is simply a resul of the weight of the cyclist's leg being forced to go in a circle. Nothing more.

What this has to do with pedaling circles I'm not sure.[/reply]

Why on earth would you or Dr. Broker or anyone restrict this analysis to the 6 o'clock position? This "interpretation problem" of the usual pedal force vector analysis is the same around the entire circle, including the downstroke, backstroke, top and bottom.

IMHO it has a lot to do with "pedaling in circles" depending, of course, upon how one defines pedaling in circles. How do you define it?

Frank

--------------
Frank,
An original Ironman and the Inventor of PowerCranks
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Re: Dr. Jeff Broker on pedaling [Frank Day] [ In reply to ]
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What I was getting at is that I don't see hwo this info changes what one might think on the subject of pedaling circles or unweighting or anything.

To me the uncrossable gulf seems to be that the folks who don't really put any faith in pedaling circles feel that way because they think it isn't worth it to try and train new muscles to do new things. They would rather just use big muscles to do more of what they already do.

The spinning circles folks say just the opposite, you CAN train the newm muscles to do new things.

I don't see how those two positions are affected by these data.
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Re: Dr. Jeff Broker on pedaling [Kevin in MD] [ In reply to ]
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In Reply To:
To me the uncrossable gulf seems to be that the folks who don't really put any faith in pedaling circles feel that way because they think it isn't worth it to try and train new muscles to do new things. They would rather just use big muscles to do more of what they already do.

The spinning circles folks say just the opposite, you CAN train the newm muscles to do new things.

I don't see how those two positions are affected by these data.

Read the last sentence of the quote I posted: it isn't about training "new" muscles to do "new things" (or just read this: http://www.me.utexas.edu/...Papers/essr30(4).pdf).
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Re: Dr. Jeff Broker on pedaling [Andrew Coggan] [ In reply to ]
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"" Understanding those non-muscular effects could prevent a coach from engaging in a counter-productive effort of trying to encourage a rider to eliminate forces which actually come at no energy cost. Indeed, the effort to eliminate them can actually cost a rider energy and efficiency."

i believe this is what AC was referring to. in this instance it does apear the man is trying to say that the " scrape the poo off the shoe " technique might be counterproductive. which, in some circumstances it may well be. there is some merit in pointing out some coaches make too big a deal about that.

it has little or nothing to do with powercrank style riding, as i see it.

it is not really all that earth-shattering from the standpoint of claiming that standing still on a leg is a low-energy thing to do. indeed, if you think of standing climbing you stand nearly still on your leg at the bottom of the pedal stroke every revolution as a bit of a rest.

none of the assertions take into account any of the other styles of pedalling a rider uses . . . such as light-pedalling in a tailwind or draft, or after a gruelling climb, etc. the article appears to a snapshot of a predominantly academic overworded bit of info most people already knew anyway.
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Re: Dr. Jeff Broker on pedaling [Kevin in MD] [ In reply to ]
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[reply]
What I was getting at is that I don't see hwo this info changes what one might think on the subject of pedaling circles or unweighting or anything.

To me the uncrossable gulf seems to be that the folks who don't really put any faith in pedaling circles feel that way because they think it isn't worth it to try and train new muscles to do new things. They would rather just use big muscles to do more of what they already do.

The spinning circles folks say just the opposite, you CAN train the newm muscles to do new things.

I don't see how those two positions are affected by these data.[/reply]

You didn't define what you (or others) mean by "spinning circles".

What I was trying to get at is, if one takes into account the effects of gravity then it is easily shown that those who do not put any faith in "pedaling in circles" because of what pedal forces show so they see no need to train new muscles will find out they are using those muscles anyhow. The only question then becomes, is there any benefit to training those muscles a little more than they are now.

This is not an either/or proposition. It is a matter of degree. Even the most die hard masher uses the hip flexors and hamstrings in order to unweight some on the upstroke. If the leg weighs 20 lbs and they are putting 2 lbs back force on the pedal on the upstroke, they are unweighting 90% of this weight through the active contraction of these muscles, lifting 18 lbs. If they have 4 lbs back force they are only unweighting 16 lbs and they have to push 2 lbs harder with the other leg to maintain the same power. If they are a PowerCranker, they are unweighting the entire 20 lbs and can push 2 lbs less with the other leg to maintain the same power (or push the same and see a power boost).

While there are other elements involved in analyzing pedaling efficiency and power (such as the direction of the forces) this is the "spinning" vs "mashing" debate in a nutshell.

--------------
Frank,
An original Ironman and the Inventor of PowerCranks
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Re: Dr. Jeff Broker on pedaling [Andrew Coggan] [ In reply to ]
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Well, it's kinda about new things, if you believe those guys, it's about teaching new muscles to do significant negative work.

Nevertheless, I don't see where the data will sway anyone from their ways of thinking.

In real life, the local spin instructor or other coach probably has never seen the vector data from elite cyclists in the first place :)
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Re: Dr. Jeff Broker on pedaling [Andrew Coggan] [ In reply to ]
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[reply]

Read the last sentence of the quote I posted: it isn't about training "new" muscles to do "new things" (or just read this: [url "http://www.me.utexas.edu/%7Eneptune/Papers/essr30%284%29.pdf"]http://www.me.utexas.edu/...Papers/essr30(4).pdf[/url]).[/reply]

I disagree with a lot of what they say. Their argument would fall apart if they had done the energy analysis at several different cadences. That being said, I think this is a pretty much worthless paper for this debate. Has nothing to do with what Broker said.

--------------
Frank,
An original Ironman and the Inventor of PowerCranks
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Re: Dr. Jeff Broker on pedaling [Frank Day] [ In reply to ]
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In Reply To:
What I was trying to get at is, if one takes into account the effects of gravity then it is easily shown that those who do not put any faith in "pedaling in circles" because of what pedal forces show so they see no need to train new muscles will find out they are using those muscles anyhow. The only question then becomes, is there any benefit to training those muscles a little more than they are now.
FWIW, Jeff doesn't think so.
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Re: Dr. Jeff Broker on pedaling [Frank Day] [ In reply to ]
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In Reply To:
I disagree with a lot of what they say. Their argument would fall apart if they had done the energy analysis at several different cadences. That being said, I think this is a pretty much worthless paper for this debate. Has nothing to do with what Broker said.
On the contrary: this was specifically the line of reasoning to which Broker was alluding.
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Re: Dr. Jeff Broker on pedaling [t-t-n] [ In reply to ]
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[reply]
"" Understanding those non-muscular effects could prevent a coach from engaging in a counter-productive effort of trying to encourage a rider to eliminate forces which actually come at no energy cost. Indeed, the effort to eliminate them can actually [i]cost[/i] a rider energy and efficiency."

i believe this is what AC was referring to. in this instance it does apear the man is trying to say that the " scrape the poo off the shoe " technique might be counterproductive. which, in some circumstances it may well be. there is some merit in pointing out some coaches make too big a deal about that.

it has little or nothing to do with powercrank style riding, as i see it.

it is not really all that earth-shattering from the standpoint of claiming that standing still on a leg is a low-energy thing to do. indeed, if you think of standing climbing you stand nearly still on your leg at the bottom of the pedal stroke every revolution as a bit of a rest.

none of the assertions take into account any of the other styles of pedalling a rider uses . . . such as light-pedalling in a tailwind or draft, or after a gruelling climb, etc. the article appears to a snapshot of a predominantly academic overworded bit of info most people already knew anyway.[/reply]

I don't believe that teaching someone to "scrape the poo off the shoe" is an attempt to "encourage a rider to eliminate forces which actually come at no energy cost." A horizontal force backwards does nothing to reduce the downward force of gravity and would only add propulsive force at this point in the stroke. Adding propulsive force in order to go faster is the goal isn't it?

--------------
Frank,
An original Ironman and the Inventor of PowerCranks
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Re: Dr. Jeff Broker on pedaling [Andrew Coggan] [ In reply to ]
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Yo can see this in action when you remove one pedal from the crankset, the other pedal naturally wants to drop to the 6 o'clock position -- with it's own gravitational force. In other words, gravity takes the pedal down to the bottom. It's a crude comparison but is this what broker is talking about? That the downstroke comes naturally and we should not expend energy trying to alter/eliminate it?

~ AB ~
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