Different size leg muscle and software to compensate

Does anyone else have different size quads and calves?
I’m right handed, but don’t thing that makes any difference. My left leg has a larger quad muscle than the right.
I’d say I have what can be described as climbers’ legs. 478 mm left vs 463 mm right circumference. Not quite the 730 mm of Robert Forstemann!
It is because I have a left side only PM? When on the turbo and needing to increase power, I naturally apply more force with the left. As any input with the right does naff all. It might not seem much, but over a year of TR, and who knows how many intervals, my left leg has ended up doing more work than my right.

Now I understand SLD and the limitations of a left side PM, but could the software not look at power in relation to cadence? ie, power and cadence in a fixed gear will be proportional. Now, if cadence stays the same, power can be inferred from that. So if I increase the cadence with my right leg, power should go up. Or if I increase the force with my right leg and cadence stays the same ( reduced force from my left ) power should stay the same too. 250w is 96 rpm in a certain gear on my trainer. So that will still be true regardless of which leg is turning the cranks.

This relies on the user not changing gear, but then you are only cheating yourself. And I suppose some form of learning from the TR software.

Unless I have seriously missed the point here!!

I wonder if you are thinking about this in the wrong way…

I’d be focussing on smooth pedalling rather than mashing down more power with one leg. On one of the workouts the coach tell you to imagine pushing your toes into the front of your shoes at the top of the pedal stroke and imagine scraping something off the sole of your shoe at the bottom.

It’s funny you posted this because My left leg is more defined than my right leg and I’m also using a single sided PM. I honestly never payed attention until I started riding so maybe it’s always been that way? I felt like maybe subconsciously I was always hammering harder with my left leg while Zwifting knowing I’d get a faster response. So now I try to make a conscious effort not to do that. By the way I’m left handed so that’s probably not important. This really makes me want a dual sided meter

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I too am left leg dominant. I’d been using Virtual Power for years, and I didn’t realise that I have an imbalance until I bought a single-sided crank power meter few months ago. I found it really frustrating and I’ve ended up buying a smart trainer with a built in power meter as well. I’m trying to use the two meters together to correct the imbalance (allowing a very slightly inflated figure from the crank meter because of its different placement), but it’s hard work. Even harder because in my case the difference varies according to how much power I’m putting out and how tired my legs are.

How did you discover an imbalance with a single sided powermeter?

While this is not specificically to do with my muscles, but different length leg, may help.

I broke my right leg a few years ago motorcycling, but always thought it was dominant, but having recently gone from single sided Stages, to dual assioma, discovered my left leg is dominant.

Im working on getting the pedalling from current 54/46 towards 50/50 and fix up some left sided soreness/issues.

  1. Proper orthothics for my cycling shoes. (I have pronation in my right and its slightly shorter than left).
  2. Cleat spacers and new bike fit.

So far the cleat spacers have improved things, just waiting on the new XP3 Foot levellers.


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I discovered it quite by accident. When I got the power meter I was mid-plan and I wanted to finish the plan using Virtual Power before switching over. In the interim, I connected the power meter to my Garmin Edge out of curiosity (I was expecting to see a difference in Virtual Power numbers verses a power meter and was keen to see ‘real’ figures). What I noticed from the files was that there was a difference, but that difference varied a lot depending upon how easy or hard I was going, or how fatigued my legs were. So looking for some explanation I went to a local gym to use a Watt Bike to see what that told me. Sure enough there was a big difference, at times as much as 60/40 L/R at endurance/recovery levels, but it disappears by VO2 max levels. I injured my knee on the weaker leg 3 years ago and I had to take a lot of time off the bike. I wonder whether the imbalance started then, or whether it’s always existed. There is also a slight visible difference in the size of my legs - one is even skinnier than the other. :slight_smile:


This really makes me want to upgrade my Pioneer single to dual. The Pioneers offer a massive amount of data (especially with the Wahoo/Pioneer head units) that I’m not currently benefiting from.

My imbalance is probably due to an old skiing accident in 2002. I had to build up my leg muscles to compensate for a weaker ACL / PCL and thus to protect them.

I am glad it’s not just me then!
Responding to @AndyGajda , I’m not mashing down on the pedals, it’s when a small increase in power is needed, like at the beginning of an interval, or when I’m sidetracked by what’s on Netflix and I need to get back up to where I need to be. It’s almost involuntary, knowing only my left leg counts towards the power readout. An extra hard push with my left gets the power back on target, then back to normal spinning. It’s all these little extra pushes that may be contributing towards the larger left leg.

So, does anyone have any input to the cadence based power smoothing? @Nate_Pearson, is this possible?