Single sided power meter with leg imbalance

Due to being retired, Tier 3 restrictions and the atrocious weather here in the UK at the moment I’ve got too much time on my hands so decided to see how my leg imbalance (Left stronger than Right) was affected by cadence changes. So I did a set of 3 minute intervals at low power increasing cadence from 60 to 120rpm and back again and measured it against my Zumo trainer set in Erg mode. The result was an approx 16% variation in power from one extreme to to the other at 120W. Presumably this is mainly due to the Force component of power being smaller at higher cadences as my measured leg is the stronger one. Does this therefore make a single sided PM no better than a HR monitor to set intensity for someone with a large leg imbalance?

Interesting comparison. I have no answer to your question, but would like to contribute the following to the discussion:

Due to ERG mode control of your trainer, the Zumo graph appears nice and constant. But these watts are only truly constant IF wattage reported by the trainer is indeed independent of cadence (flywheel speed).

Sorry to complicate things even further :wink:

I have a dual sided PM and see similar variation to you (~8% range in contribution from each leg which would equate to a ~16% range in the accuracy of a SS PM), so yes, personally I have seen enough L:R data that I would never use a single sided PM.

My other conclusion is that if you ever get into Zwift racing you should clearly use the 4iii PM and keep the cadence low!

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What is your FTP ? why i ask this question is because my L/R balance is much beter close to my FTP instead of the lower power ranges .
How do you know your Left is your stronger leg on the bike ? have you done rides with a dual powermeter ?
My right leg is stronger but on the bike this is not noticeable .

I take your point. I got some Assioma Duo’s to replace the single sided PM. When I get the chance I’ll compare them with that on the Zumo using power match and see if I get similar results.

FTP is circa 230W. My Assioma Duo show a L/R imbalance of between 58/42 and 55/45 over a complete ride depending on intensity and presumably cadence.I’ve no idea why there is such an imbalance, no injuries except perversely i have had/am having problems with my left knee. Keyhole surgery 8 years to remove part of the cartilage but the problem seems to be reoccurring at the moment. My impression is that as the intensity increases and/or I fatigue it does balance out.

Following this topic as I’m in exactly the same position even down to considering getting the Assioma upgrade. I sometimes run the left pedal and trainer at the same time (Wahoo KICKR Core) and it’s normally about 8% lower out using 30s averages. I can also feel that my left leg is weaker but with a bit of concentration on technique it does tend to correct itself slightly.

For now, I mentally set my zones about 10% lower outside and this also seems accurate as I’m getting faster speeds on segments for reported less power (compared with when I was using dual-sided).

so you have quite an imbalance , did you have a bike fit ? any difference in leg length ? Maybe go to a fitter that is known in your area and talk about your issues he might have a solution to your imbalance and knee problems because i think the 2 will be related .

@Thomas_De_Kesel 0ne leg is very slightly shorter than the other (4/5mm) but at 64 years old I strongly suspect i’ve adapted to it. I’ve had bike fits over the years and am actually thinking about getting another. I don’t mind paying for a good fit but would object to paying for a poor one and my I’m a little sceptical about them as in my limited experience they all try to sell you stuff which they say is essential to the fit. I had the knee problem before I started cycling and it only really occurs when I start doing a load of walking/hiking. No pain whatsoever when cycling… My left leg could be stronger due to 40+ years of 30-40,000 miles a year in a manual car constantly depressing the clutch - who knows though

Hi @carytb if you don’t have any issues on the bike i would not go for a bike fit , maybe do some pedal drills , 4 quadrants and ILT ( isolated leg training ) to work on your technique and see if this makes a difference in your L/R balance ?

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I carry a permanent injury to my right knee and used a single sided power meter (LHS) for the summer. I did an outside FTP test which I used for my rides through Spring until this weekend and while this wasn’t ideal it would help me target my endurance zone as my focus was on riding with mates and as such I didn’t follow a structured training plan.

My ftp test is scheduled for tomorrow on my Flux so it will be interesting to see how my FTP benchmarks tomorrow.

From what I’ve worked out ( man maths) I am looking at a 20%/25% difference between my left and right leg although I’m hoping to get a more accurate picture tomorrow

Outside and inside watts on difference equipment are hardly comparable.

Does this therefore make a single sided PM no better than a HR monitor to set intensity for someone with a large leg imbalance?

Heart rate is influenced by lots of outside variables which is what makes it so unreliable, in my understanding. Power, single or dual, should still be consistent from one workout to the next.

I’m fairly new to TR but use a single-sided power meter and have researched the same. My first single leg drills shined a light on my own imbalance, but after completing several of these drills and practicing on the trainer and outside, I feel like I’m closing the gap a little just through pedal technique. My left leg is noticeably sloppier at high cadence and fatigues quicker. Since I’m on a left crank power meter, my FTP is probably lower than it “actually” is, but since it’s consistent from one workout to the next and I’m definitely pushing myself in these sessions, it seems to be a perfectly reliable metric to use.

Not really answering your question, just sharing my two cents!

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This isn’t only from leg imbalances, you’ll lose a few percent on the drivetrain too. (Contrary to what some people think no amount of calibration can fix that, you’re just measuring power at different points and it always sits in-between the trainer and the pedals)