Perhaps you just unweight much better w/ your right leg? The Quarq would count that as power generated by your left leg.

Doubtful. You should have noticed this when installing rings because your crank arm would have covered a bolt hole, much like the hidden bolt SRAM setups.

Probably this, if you are pulling up with your right leg then the Quarq will count it as the left leg. Quarq and similar meters like power2max don't measure true left right balance, they measure left half of pedal stroke and right half of pedal stroke. To get true left right balance you would need either a pedal system or dual pod system like Pioneer.

I'm going to question your assumption that your left leg is stronger. I'd get some Vector pedals or something and verify (if you care).

And maybe you should care now. Because if it really is an unweighting-of-right-leg issue, that 5% sounds like the training unicorn: absolutely free power. And 5% is a lot.

That's quite an assertion. You sound like you've been drinking the FD Koolaid;)

Hugh

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Genetics load the gun, lifestyle pulls the trigger.

OK, I deserved that. That was kind of embarrassing now that I read it. I realize it's not that simple. Legs are heavy and the power to lift them has to come from somewhere. But, say 15W of left leg down-stroke power @ FTP to lift the right leg sounds like the *wrong way* to lift the right leg. Just because FD was largely off-base doesn't mean that you want your off-power leg to be a giant wad of dead meat.

When I get an overall imbalance in L/R from my quarq, it is usually from the periods where I am coasting or waiting at stoplights at which time it is 100% one leg, 0% on the other. Rides with long and steep descents therefore get the worst overall balance. When you go into the data, does the balance look different from the 45/55 when you are actually pedaling?

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I wouldn't worry about it. For the most part L/R balance is a rubbish metric as asymmetry is normal (5% isn't much when you take margin of error into a account).

Well, the assumption is that my right leg is stronger, not my left....but I honestly know this to be correct. It all stems from my lateral release...part of my quad was actually detached during the surgery. The muscle fires, but it doesn't pull on anything down by the knee. I have a permanent 10-15% strength deficit on my left side. This was likely compounded during my rehab, where I was probably heavily favoring my right side on the bike (was a pure cyclist then).

Likely never would have known it had I not ridden PowerCranks (left side would reach complete muscle faialure in about 10-15 secs) or gotten into tris (all my injuries have been on my left side because of this imbalance).


yeah, I'm not really concerned about it....I just thought it was interesting since the numbers were in complete contradiction to what I feel pretty comfortably is the reality. Didn't know if the orientation of the spider was how the Quarq determined which side was left or right...if so, then having it 180* would explain the difference (i.e. it is actually my right leg that is stronger).

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Until the asymmetry isn't normal. And you don't know it's not normal without a metric.

I found it very useful in improving total power output in the neuromuscular range of power (>1000W). Basically I found that I was about 50/50 until about 3*FTP, and things started to go haywire. Then verified an underlying issue....e.g. I could do one-legged squats all day with my left leg but would instantly collapse into a puddle if trying just one with my right leg. Fixed that through some physical therapy - now I'm pretty balanced, and my standing start in track is much better, etc.

So one person's "rubbish" is another person's useful metric, sometimes.

'For the most part'...

How many triathletes need 1000w at any time? Besides, normal for one isn't the same for another and there are far more useful metrics that should be examined before looking at something so low level.

Yeah, I agree it's an edge case. (Though this forum isn't just for triathletes).

But on the other hand the data is so easily available for a lot of power meters, that there's minimal cost to providing it. I agree it shouldn't be stressed over, and it's easy to be distracted by it, but, on the other hand, if you glance at it and see 70/30. (Like I did), that's a useful tip that *something* is going on. It's even a useful tip that a PM is malfunctioning, as I've seen with one person's Vector PM.

A Vector malfunction... Never heard of such a thing! ;)

Where are you reviewing the L/R balance metric? I haven't been paying attention lately, but this used to be reversed in TrainingPeaks software. I have a similarly consistent imbalance with right showing stronger than left in the range you mention.

I have used 3 generations of Quarqs on my CT and don't see that much power variation as long as the Quarq is zeroed and the CT is calibrated at operating temps. I use PerfPro and it is very apparent when one of the units isn't calibrated properly. I guess I should qualify, that I don't 10 watts variation at the loads I ride. Lol. %power delta between the devices might be more applicable for comparisons.

I was looking at the L/R data in Garmin Connect.

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

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That would make sense.

This was a CT ride....so no coasting.

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

There goes that theory then :)

The weight of one leg descending pretty much covers the weight of the ascending leg. Unless the cranks are uncoupled or you are one legged, there is very little energy required to lift the legs while pedalling.

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10W is a lot if it's powetrain losses IME. I would download the Qalvin app and get my hands on an ANT+ dongle and check the torque slope of the Quarq to make sure it's calibrated correctly. Check the PT too while you're at it. If that checks out fine, the you might want to figure out what's bad in your drivetrain ;-)

As far as the L/R goes...yeah, pulling up significantly with your right would show up as a "bonus" for the left leg in the way that a Quarq estimates L/R balance...

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Power13 wrote:

So, how does the Quarq determine L vs R leg?

http://alex-cycle.blogspot.com.au/...-out-of-balance.html


Quarq is measuring forces downstream of the BB, so it reports a "pseudo power balance".


IOW it measures forces from both legs for each half of the pedal stroke and does the power balance split that way.

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Exactly...and it also leads most to wrongly ass-u-me that when individual pedal data shows a downward force on the rising pedal that it means the rider is actively resisting the pedal stroke or something...when it's actually just the reaction force on the pedal of the leg being "lifted" by the falling mass of the opposite leg (for "free") :-/

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Right. That's how it's supposed to be. But I don't consider 5% of power "very little." 15W @ 300W is a lot of power. And that's the *difference* between L/R, not the total. That's why I was suspecting a "pathological" unweighting issue, e.g. the legs actually fighting each other for a moment vs. just a more mundane assymetry.. Assuming this isn't just noise, measurement error, bad L/R model in the Quarq, etc.

Well assuming it's accurately reporting pseudo power balance, all you know is that if it occurs at 300W, then both legs report 30W more during one downstroke than during the other.

But there is no way to ascertain why such a pseudo power balance is reported since the data is the net value from both legs. It requires at minimum an independent measurement of the forces applied to each crank arm or pedal in order to answer the question, at least in part. e.g. it could be active upstroke on one side that causes the reported pseudo imbalance rather than active opposition.

But the premise that one needs to apply extra power to lift a leg while pedalling isn't correct, since the energy to do that is provided by the other descending leg.

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Right. And if both legs are providing a 30W difference in power in one position vs. the other, that might be worthy of investigation. Generally speaking, the pedal stroke should be reasonably symmetrical, excepting the well known swings in L-R power so popular to bring up in Stages threads. I guess it would depend on when and how the difference is occurring. But 5% is a reasonable threshold for raising an eyebrow. In my opinion.


Right....in my first post in this thread I think I said, "Get some Vector pedals to verify" with the unspoken intent being to get independent L/R measurement.


And that premise is based upon the premise of perfect unweighting of the rising leg. If some assymetry in timing, etc, is resulting in the rising leg actually exerting some sort of resisting force against the pedal, that would be *one* explanation for both legs providing 30W more power in one orientation vs. the other. And might be worth looking into.

Or you you could just shrug and say, "5%, whatever" and move on with life, and stop trying to explain data with no obvious answer. Which, odds are, is probably just fine in the grand scheme of things.

Dual-sided measurements + WKO4 FTW.

The basic physics principle applies whether or not one is pulling up or actively resisting. I never said anything about perfect unweighting, besides that's a red herring wrt to the power required to move legs up and down when they are connected to coupled cranks.

Whether or not it's worth looking into is not a judgement I think you can make with pseudo power balance data. It requires the right tools for the job.

Equally a pseudo power balance might report 50:50 which might initially suggest no further investigation required but in reality you may actually have a power imbalance that may or may not be worth looking into.

Can you see the problem?

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Possible even with 'true' balance measurements.

Looks like this may the correct answer.....part of the workout today included single-leg drills (I don't make the workouts, just ride 'em). The L/R balance from these intervals read as ~80/20 in favor of whichever leg was being used. Obviously since I was not using the other leg in these drills, the Quarq was interpreting the pull phase of my pedal stroke as power being applied to the other side.

Interesting....thanks for everyone's input.

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

I think that's a sub-optimal way to diagnose your potential problem. I'd bet your pedal stroke is a lot different when pedaling with 2 legs rather than 1. IMO, you can't just pedal with one leg and draw conclusions about pedaling with two legs.

Of course my pedal stroke is different with one leg vs. 2.....

Did you read my other posts on this thread? I know my right leg is stronger than my left, so the fact that my L/R balance comes out as 55%L and 45%R made no sense. Combine this knowledge with the data from today's ride and the insight from one of the smarter guys around re: power analysis and you can reach a logical conclusion as to why it reads that way.

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

Just to be clear, all that the difficulty you have with your left leg using Powercranks is actually telling you is that you left leg hip flexors are a good bit weaker than those of your right leg. Your left leg extensors may in fact be stronger than those of your right leg. If this were the case the "pseudo balance" shown by your Quarq would show the pattern you're seeing.

YMMV,

Hugh

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Genetics load the gun, lifestyle pulls the trigger.

Yes, I have. To be blunt, I think you're wasting your time. The Quarq L/R data is not actionable data. It's neat to look at, but it's not measured independently, so it's nothing more than a novelty.

Just because you have a muscular issue with one leg, and you know it's stronger, doesn't necessarily mean your pedal stroke is imbalance as a result. I have a strength difference in my legs as well. I can do 10 pistol squats with my right, and 3 with my left, and yet my pedal stroke was measured as 49/51 during a 20' FTP interval on a set of Vectors.

If I was just looking at my PC experience, you may be right....but when you combine the PC experience with the end result of my lateral release (part of my quad is detached and I have a permanent 10-15% strength deficit), it tells a different story.

I'm not looking at just one piece of evidence and saying "Ah-ha!!".

Again, I'm not really concerned about the measurements....it was the fact that it was in such sharp contrast to what I am reasonably confident the reality is that I asked the question.

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

I have a Dzero and a Polar M450, the head unit does not show Power balance, nor Polar Flow website, any one has the same issue?
It might be something wrong with the Polar BLE protocol, read somewhere on dcrainmaker comments.