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Left-Right Power Balance: What is considered "good"?

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Left-Right Power Balance: What is considered "good"?

Old 08-23-23, 11:05 AM
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Left-Right Power Balance: What is considered "good"?

For context: I have a leg length discrepancy I've compensated for my entire life (Left is 2cm shorter than right). My bike fitter recommended that I get a dual sided power meter to make sure that it's not affecting my power balance and stroke, so I got one. Now, as I look at my data, I realize I had never actually thought about what a good power balance really means.

My power balance fluctuates a bit of course, sometimes though a bit more than I'd like. I recently re-adjusted my power meters (Garmin Vector 2) and had a ride this morning. The results:




By comparison, here are the results from a ride from before I re-adjusted my power meters:




So there are some differences, particularly seeming unbalanced in the most recent ride. Got me thinking about the question in the title: What is a good or okay L/R balance anyways? And how does power phase factor into it? Interested in opinions or your experiences.
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Old 08-23-23, 01:38 PM
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I don't think anyone really knows. However very far apart probably indicates a issue. But you aren't anywhere near very far apart.

Bikes are pretty light and move in surges as your power builds during your pedal stroke. So your speed is varying anyway despite the fact your cyclometer doesn't see those small excursions happening. So one being a tad higher than the other doesn't seem like much of an issue to me.

I've always felt that trying to build up the lesser leg over the other leg is just simply loosing losing over all power as you aren't building up both legs as much as possible.

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Old 08-24-23, 09:03 AM
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Rather than "What is a good or okay L/R balance anyways?" a better question is "can I achieve my riding goals without pain or limitation related to asymmetry?" Are you limited in distance, or duration, or speed, or some other goal that you're interested in? Your left leg isn't going to grow so your particular level of asymmetry may have more to do with adjustments to the bike than adaptations to your pedaling: for example, maybe (and I don't know, but maybe) different lengths for the right and left cranks might help you achieve your goals. Discuss that with a fitter.
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Old 08-24-23, 10:15 AM
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My L/R balance averages around 55/45 when I think to look at it. I donít know of any length differences between my legs. Iíve mentioned it to both a bike fitter and cycling coach who have both said that I am well within the normal range and not to worry about it, so I donít.

I believe it was on the trainer road podcast recently that I heard someone mention a study about how it seems that some people may be keeping some power in reserve with one leg. This comports with some of what Iíve seen- during hard intervals or climbs my power evens out and sometimes tips the other way.
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Old 08-24-23, 02:13 PM
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Our bodies are only symmetrical to a first approximation. The contents of the chest and abdomen are obviously not symmetrical at all and our limbs are quite different when viewed in detail. Left-right differences in muscle size and strength, and speed, and dexterity of movement are significant and related to differences in representation in the brain. This specialization has to be adaptive at some level and, as RChung points out, there are energetic and anatomical reasons to question whether complete symmetry is optimal. This might be like the mythical "round" pedal stroke, which seems sort of intuitive on a naive engineering basis, but is biomechanical and energetic nonsense.

That said, dual PMs have got to be useful for working on real congenital asymmetries, bad habits, and injuries. I ride occasionally with a guy who might benefit. I can barely stand to watch what he does with his left ankle.
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Old 08-25-23, 09:32 AM
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Originally Posted by force10

I believe it was on the trainer road podcast recently that I heard someone mention a study about how it seems that some people may be keeping some power in reserve with one leg. This comports with some of what Iíve seen- during hard intervals or climbs my power evens out and sometimes tips the other way.
Yeah Iíve heard about that too and see it in my own data. When riding at relatively low power I tend to favour my right leg and it evens out at higher power when it might actually matter. In either case I donít see big variations, typically 5% offset at most.
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Old 08-25-23, 09:50 AM
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I've always wondered what the developmental trigger is for endoderm to break symmetry during differentiation, whereas mesoderm and ectoderm (which includes the CNS) maintain (at least to a first approximation) bilateral symmetry.

My main concern is how one would actually address a significant power asymmetry, assuming it exists. Ten years after breaking an ankle and being on crutches for 4 months or so, I can still see muscle differences. I've never checked to see if there are power differences, but I am so slow anyway, any power meter would be wasted on me.
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Old 08-25-23, 09:54 AM
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Originally Posted by Polaris OBark
I've always wondered what the developmental trigger is for endoderm to break symmetry during differentiation, whereas mesoderm and ectoderm (which includes the CNS) maintain (at least to a first approximation) bilateral symmetry.

My main concern is how one would actually address a significant power asymmetry, assuming it exists. Ten years after breaking an ankle and being on crutches for 4 months or so, I can still see muscle differences. I've never checked to see if there are power differences, but I am so slow anyway, any power meter would be wasted on me.
My impression about significant power asymmetry is that it suggests a physiological discrepancy (like different leg lengths) or equipment setup problem that then needs to be addressed, but asymmetrical physiological development (e.g. that one guy in "Lady in the Water" who only works out one half of his body) would probably be much more of a puzzle to fix.
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Old 08-25-23, 09:59 AM
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Originally Posted by MoAlpha
Our bodies are only symmetrical to a first approximation. The contents of the chest and abdomen are obviously not symmetrical at all and our limbs are quite different when viewed in detail. Left-right differences in muscle size and strength, and speed, and dexterity of movement are significant and related to differences in representation in the brain. This specialization has to be adaptive at some level and, as RChung points out, there are energetic and anatomical reasons to question whether complete symmetry is optimal. This might be like the mythical "round" pedal stroke, which seems sort of intuitive on a naive engineering basis, but is biomechanical and energetic nonsense.

That said, dual PMs have got to be useful for working on real congenital asymmetries, bad habits, and injuries. I ride occasionally with a guy who might benefit. I can barely stand to watch what he does with his left ankle.
So my curiosity is getting the best of me, but I have to ask: what does he do with his left ankle?
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Old 08-25-23, 10:23 AM
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Originally Posted by sir_crash_alot
So my curiosity is getting the best of me, but I have to ask: what does he do with his left ankle?
Oh, man. I can't picture it clearly enough to give an anatomical description, but it looks like he's trying to spool up yarn with his foot. He also runs his seat too high.

He's also 10 years younger than I and can clean my clock.
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Old 08-26-23, 02:31 AM
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My recently developed L/R power imbalance has been on my mind, so, this thread is quite interesting. I don't have any answers but only questions.

If my L/R is 45/55, does that suggest a lost of 10% at threshold? (due to left leg slacking off)

What is related or at least coincident time-wise is a certain pain where the left glute connect up by your butt to the greater trochanter. As power increases into Tempo, that area starts to get sore almost like a cramp and I can only do a threshold effort for perhaps 10 minutes before it becomes very uncomfortable. I had had an accident and when they released me from the trauma center, despite complaining of hip pain and asking how the heck was I going to walk, pain in the left hip was not going away. Long story short, the greater trochanter was also fractured, an Ortho surgeon looked at my CT from the trauma center and showed it to me. He had been pretty casual about it, like, well, you have a bum leg now.

Assuming the attachment of the glute to the greater trochanter either developed scar tissue or perhaps calcification, would a chiropractor be who to help me rather than a medical doctor? PT? Stay the hell is zone 2? It isn't really a medical problem not be to able to ride a threshold. Maybe a Chiro?
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Old 09-07-23, 02:24 PM
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Originally Posted by MoAlpha

That said, dual PMs have got to be useful for working on real congenital asymmetries, bad habits, and injuries. I ride occasionally with a guy who might benefit. I can barely stand to watch what he does with his left ankle.
Yeah, similar. There's one guy I ride with who always has his entire torso a bit twisted to the left when he rides. Even though this is only evident on the bike (he walks straight), I hesitate to bring it up b/c maybe he has some injury or deformity and it's not just a question of poor posture. But those aside, I'm sure his power values are highly asymmetric.

Your ankle guy might also have an underlying health reason.
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Old 09-07-23, 07:45 PM
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Originally Posted by GhostRider62
My recently developed L/R power imbalance has been on my mind, so, this thread is quite interesting. I don't have any answers but only questions.

If my L/R is 45/55, does that suggest a lost of 10% at threshold? (due to left leg slacking off)

What is related or at least coincident time-wise is a certain pain where the left glute connect up by your butt to the greater trochanter. As power increases into Tempo, that area starts to get sore almost like a cramp and I can only do a threshold effort for perhaps 10 minutes before it becomes very uncomfortable. I had had an accident and when they released me from the trauma center, despite complaining of hip pain and asking how the heck was I going to walk, pain in the left hip was not going away. Long story short, the greater trochanter was also fractured, an Ortho surgeon looked at my CT from the trauma center and showed it to me. He had been pretty casual about it, like, well, you have a bum leg now.

Assuming the attachment of the glute to the greater trochanter either developed scar tissue or perhaps calcification, would a chiropractor be who to help me rather than a medical doctor? PT? Stay the hell is zone 2? It isn't really a medical problem not be to able to ride a threshold. Maybe a Chiro?
You know the caveat that I have no medical expertise and that you should find somebody who does, but this sounds like it might be trochanteric bursitis, which I've had before. In my case, I had an injury from a minor bike-fall that seemed like it was no big deal, and then some months later the pain developed. Pain symptoms on the bike were similar to what you describe

In my case, PT exercises helped some, and eventually it mostly went away. Sometimes I still feel it.

I hope you find some way to get relief.
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Old 09-08-23, 04:40 AM
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I'm crooked when walking from a prior back injury, and I injured my knee last year in a bike crash.

L/R varies from 43/57 to 47/53. My left platform offset is 9mm more than my right - i keep moving my cleat towards the outside of shoe with little improvement. Before the crash I was 48/52.

Interesting that my biggest variance seems to come on light/easy days. My dominate leg does most of the work when just spinning along.

I need shims and a professional bike fit. But locally, the only option I have for a comprehensive fit that includes shims/addressing L/R balance is over $500 plus parts/equipment... so that will wait a bit.
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Old 09-08-23, 07:00 AM
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Originally Posted by Jughed

Interesting that my biggest variance seems to come on light/easy days. My dominate leg does most of the work when just spinning along.
I think thatís fairly typical. At low power it doesnít really matter unless something hurts because of it.
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Old 09-08-23, 09:20 AM
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Originally Posted by MinnMan
You know the caveat that I have no medical expertise and that you should find somebody who does, but this sounds like it might be trochanteric bursitis, which I've had before. In my case, I had an injury from a minor bike-fall that seemed like it was no big deal, and then some months later the pain developed. Pain symptoms on the bike were similar to what you describe

In my case, PT exercises helped some, and eventually it mostly went away. Sometimes I still feel it.

I hope you find some way to get relief.
Thanks, I will get that checked but am and EMG and MRI lumbar done next week. My feet are numb and left knee has neurological type pain for no apparent reason. The Neurologist scoffed at my question whether cervical spine stenosis in the canal with the cord compressed could cause lower limb issues.

I have found PT to be a crapshoot but you might be correct. I'll try to get a script for PT. As long as I don't ride too long for too hard, it is fine. Crazy
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Old 09-08-23, 12:52 PM
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Originally Posted by GhostRider62
Thanks, I will get that checked but am and EMG and MRI lumbar done next week. My feet are numb and left knee has neurological type pain for no apparent reason. The Neurologist scoffed at my question whether cervical spine stenosis in the canal with the cord compressed could cause lower limb issues.

I have found PT to be a crapshoot but you might be correct. I'll try to get a script for PT. As long as I don't ride too long for too hard, it is fine. Crazy
My doc prescribed a professional PT firm that treats pro athletes. They fixed a long term radiating pain problem for me.
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Old 09-12-23, 07:00 AM
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I once took one of these tests with a fitter. I was 67 at the time. I was assessed at 86% efficiency with no imbalance in legs. The fitter said, "How are you doing that?" I told him that when I got into cycling in my mid-30's I read a book that suggested riding rollers. So, every winter I did. My introduction to cycling was on rollers. He said, "Of course."
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