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L/R pedal powermeter data and peak power arcs

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L/R pedal powermeter data and peak power arcs

Old 01-16-20, 02:59 PM
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ExMachina
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L/R pedal powermeter data and bike fit

Road cyclist here. Just got dual sided power meters (pedals) and I have learned a LOT about how I pedal (...er, or at least I have a lot of data on how I pedal )

One of the many things that I have noticed is that I can alter my "Peak Power Phase" (which is defined by Garmin as the number of degrees through which each leg delivers 50% of it's total power) simply by moving the saddle up/down 1mm or 2mm (!) For example if I move my saddle DOWN 2mm from my normal position,my PP arc goes from 70 degrees to 77 degrees which seems like a significant change (my full power arc is ~225 degrees). So assuming my total power output has not dropped (which I haven't tested yet), it seems like lengthening the PP arc could reflect a smoother delivery of power (ie, so maybe my normal saddle height was a little too high).

So (even if my interpretation of this is incorrect) it sure seems like such power phase data could be used to help dial in position for optimal performance (at least for a given discipline). However, I can find very little information on this topic but am sure it must exist. Does anyone know of any good resources on this (or have any info they could share)?

Last edited by ExMachina; 01-16-20 at 03:13 PM. Reason: title change
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Old 01-16-20, 04:26 PM
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Originally Posted by ExMachina View Post
So assuming my total power output has not dropped (which I haven't tested yet), ...
If your power doesn't change, what difference does how you apply the force make?
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Old 01-16-20, 05:20 PM
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My guess is that a shorter arc will tire one's legs more quickly at the same power. There might be a simple test: in erg mode, set the power on your trainer to say 110% FTP, then change the length of your peak force arc. See what happens and report.

I realize that this test is more rigorous than one would encounter on a climb, still I think the principle is the same. I know when I want to do long (for me) VO2max intervals, I get noticeably less fatigued if I engage my hams, glutes, and calves to increase the length of my power arcs.
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Old 01-16-20, 05:56 PM
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Originally Posted by asgelle View Post
If your power doesn't change, what difference does how you apply the force make?
I would say that "how you apply the force" is extremely important in cycling (individualized cadences are an example of this).

In terms of the pedal stroke, superficially: Power=(Force*Distance)/Time

So decrease the pedal stroke's distance (its arc length) and the rider must increase the force to keep the power the same. So there's likely an optimum arc length where fatigue is minimized
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Old 01-16-20, 05:59 PM
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Originally Posted by ExMachina View Post
So there's likely an optimum arc length where fatigue is minimized
Since fatigue is the inability to maintain the desired power, by definition, changing fatigue means changing power. You can't have it both ways, if different pedal strokes don't change power, fatigue must be the same; if fatigue is different, you can't be seeing the same power.
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Old 01-16-20, 11:36 PM
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Fatigue is more than just putting less power out, you still feel fatigue when you get off the bike.
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Old 01-17-20, 12:24 AM
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I can do a lot of hard riding, especially climbing, or very long rides. I will feel fatigued and experience a power loss. However, I also can do some decent climbs and short rides of 25 miles for instance and at no time feel fatigued. But when I go to push the pace as fast as I can for several miles or on longer climbs even though I definitely do not feel fatigued or weaker but in reality, I still am actually experiencing fatigues as indicated by reduced power and slower speeds at the same subjectively perceived output.
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Old 01-17-20, 07:10 AM
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Originally Posted by Seattle Forrest View Post
Fatigue is more than just putting less power out, you still feel fatigue when you get off the bike.
The commonly accepted definition of fatigue in the context of exercise physiology is, as I wrote, the inability to produce or maintain a level of effort.

Just as with efficiency, people redefine it to mean whatever they want it to mean with the result no one knows what the other is talking about and we get into endless arguments because of the confusion.
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Old 01-17-20, 09:28 AM
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Originally Posted by asgelle View Post
Since fatigue is the inability to maintain the desired power, by definition, changing fatigue means changing power. You can't have it both ways, if different pedal strokes don't change power, fatigue must be the same; if fatigue is different, you can't be seeing the same power.
Fatigue is also related to time. For example I know I fatigue much faster (at the same power output) if I try to keep my cadence artificially high. So there are most definitely better/worse ways to deliver energy to the bike.
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Old 01-17-20, 09:32 AM
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Originally Posted by ExMachina View Post
I disagree. Fatigue is a function of time also. For example I know I fatigue much faster (at the same power output) if I try to keep my cadence artificially high. So there are most definitely better/worse ways to deliver energy to the bike.
I don't see what you're disagreeing with.I never said different pedaling styles don't result in different times to fatigue, only that as long as power remains the same, fatigue is also equal.
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Old 01-17-20, 01:34 PM
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Somebody here gets it.

Until you get grossly out of fit range for a riding position (hoods, drops, time trial, bar tops), you won't see an appreciable difference in performance.

Next, good luck taking the "pedal in circles" bull **** or some other super thought aware pedaling into some hard intervals. You get efficient riding hard by riding hard, often. Your body is forced to figure out how to adapt to the stress. Could be a touch of cadence, could be a touch of pedaling style, etc....

Also, this awareness isn't available "in a race" or when paying attention to your wheel in a paceline. So, if you're not a pro or someone riding a LOT..........you won't reinforce the habit through some kind of situational awareness just during an easy enough workout that you can bother to watch such things.

You can spot the 'onset' of fatigue after the fact with watching your cadence go from a robot metronome like 100rpm on the do to a little sawtooth pattern later in the interval as you approach fatigue.

If I were you, instead of too much worry about that.......I'd set the seat up with basic normal fit rules and use those pedals to do some structured training. Again, you get efficient riding at 105% by riding at 105%. Not by riding at 50% and staring at a pedal efficiency metric.
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Old 01-18-20, 11:11 AM
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Originally Posted by asgelle View Post
I don't see what you're disagreeing with.I never said different pedaling styles don't result in different times to fatigue, only that as long as power remains the same, fatigue is also equal.
you quoted me too quickly (before i could edit that out). i agree that we don't disagree
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Old 01-18-20, 11:27 AM
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Since this thread seems to have gone off the rails almost immediately, I'd like to restate my original question:

Are there any resources that anyone knows of (websites, book, scientific paper) that discuss how a power meter can be used to optimize position on the bike?

If not that's cool.
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Old 01-18-20, 08:17 PM
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I have the Garmin Vector 2 L/R. Via the Garmin 820, I can generate all kinds of graphs. I have not found any use for them yet, supporting material or a coach that is interested in the data.
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Old 01-18-20, 08:40 PM
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Originally Posted by ExMachina View Post
Since this thread seems to have gone off the rails almost immediately, I'd like to restate my original question:

Are there any resources that anyone knows of (websites, book, scientific paper) that discuss how a power meter can be used to optimize position on the bike?

If not that's cool.
I don't know, but I do know that some fitters do that. They change position elements and monitor HR and power, looking for changes in power with position.

I was doing intervals again on my resistance rollers this evening and testing power arcs while suffering along. So, I'd be holding power, legs getting tired, and then without looking at my device, I'd activate my glutes and start raising my toes at ~11 o'clock. I'd look down and my power had gone up 8 watts. Then I'd maintain that motion and reduce cadence a hair, dropping my power down to where I had been trying to keep it. My legs definitely felt less stress. It took concentration to maintain that arc, but that should go away with practice.

I definitely have a saddle height sweet spot where I develop more power, mostly from pushing forward/pulling back with a particular knee bend in each spot.

The below is is a useful video to watch for pedaling action and saddle height. Though their position seems different, they're just rotated forward on the bike. Their actual position w/r to the BB isn't different. If you imagine the riders rotated back so their torsos are in the road position, you'll see what I mean. We can see their muscles fire as they go through the pedal stroke. If you watch that famous video of Pantani vs. Lance on Ventoux, you can see similar pedaling.


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Old 01-19-20, 08:03 PM
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Originally Posted by Hermes View Post
I have the Garmin Vector 2 L/R. Via the Garmin 820, I can generate all kinds of graphs. I have not found any use for them yet, supporting material or a coach that is interested in the data.
This has been my experience, too. And then last summer I injured my feet and ankles, worse on the left side. Now I have a use for L/R balance. But torque effectiveness and pedaling smoothness? Better to spend the time and effort making more watts than making these read differently, I think.
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Old 01-29-20, 04:43 AM
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Seems to me muscle memory is what drives power arc, smoothness and torque effectiveness. I'm sure bike fit can hurt your numbers, but drills that create a full smooth power delivery like single pedal and high cadence are the way to really drive improvement.
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Old 01-30-20, 08:53 AM
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Originally Posted by Carbonfiberboy View Post
Their actual position w/r to the BB isn't different. If you imagine the riders rotated back so their torsos are in the road position
Not sure what you mean, you don't believe they are more forward over the BB and that the only difference is they are rotated at the hip more?
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Old 01-30-20, 11:43 AM
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Originally Posted by jadocs View Post
Not sure what you mean, you don't believe they are more forward over the BB and that the only difference is they are rotated at the hip more?
Their entire bodies are rotated. IOW they are in the road posture, just rotated to get more comfortable in the aero position and open their chests. They might be rotated at the hip less. Look at that thigh/belly clearance. Of course they're all flat-bellies, but still.

I meant that they are rotated around the BB. Of course their position w/r to the horizontal is very different from the road position. Even with their saddles as far forward as the rules allow, they're up there on the nose. But their bodies w/r to their various parts, not w/r to the horizontal are approximately in the road position. And therefore their pedaling action and muscle usage is not very different from a rider in the usual road position w/r to the horizontal - with a big caveat: Notice that their upper bodies are absolutely stationary. These women are powerful swimmers with well-developed upper bodies, yet there is no visible upper body muscle flexure going on. They pedal with their legs. Among road cyclists, one sees some riders who bob a lot, using their more upright position to push on their legs with their body weight, Newton's 3rd law in action. This is all very interesting to me.
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