Leg Length/ Power Output

Many years ago (about 25 years I guess), I was diagnosed with a leg length discrepancy which manifested itself with ITB pain. This wasn’t diagnosed by medical scans, but by an NHS physiotherapist who just happened to be a cyclist and Commonwealth medalist. Basically, diagnosed by observation on a static trainer.

Anyway…we shimmed the shorter leg, and this improved the issue over time (along with pilates exercises pre/ mid and post long rides). However, over the years, I weaned myself off the shims and have been riding shim-free for well over a decade now.

Fast forward to now, and the advent of power meters, I’ve noticed since riding with true dual-sided meters (Veve Infocrank initially and now Assioma Duals), that the power distribution between L/R legs is always generally 6-8% biased in favour of my RIGHT leg.

Now, I know pretty much nobody has perfect 50/50, but I have started to wonder whether the slightly higher than “normal”, imbalance is perhaps to do with the leg lengths, so was considering experimenting with shims again.

The rather embarrasing part is…I can’t remember which leg was the shorter one LOL, so my question is to any biomechanics/ bike fitters/ physios out there, what would be the “expected”, answer to which leg produces more/ less power? Is a shorter leg more likely to be producing less power output compared to the longer one, or vica-versa?

Also worth noting, there is a definte difference in muscle definition in the vastus medialis of the quads, with the LEFT leg (the one that has LOWER power power balance bias), being visibly more developed than the RIGHT.

Here is my experience, which may help you:

My lower left leg is shorter than my lower right leg. Prior to putting a shim under my left cleat, my power was 53-55 right / 47-45 left. With the shim, that balance is close to 50/50.

It seems like your best bet is to determine which leg is shorter, and if that length discrepancy occurs on the lower or upper half of your leg.

Ive been there myself. My right is stronger (at the time way stronger) than the left partly because the leg is shorter and was having to work harder. It tightened the left leg IT band though which pulled the patella out of alignment in the right knee and it was like a knife going through it! Based on my experience I would guess your right leg being stronger is the shorter one but I’m no physio. With me though its noticeable when I put on a pair of 3/4 or knee warmers and the gap to the socks is significantly different.

Just out of curiosity, why did you ween yourself off shims? Seems like you trained one leg to take over more responsibility in that process.

I have a leg imbalance that I have overcome, but it was/is injury-related. I had two injuries on my right knee (torn meniscus and bursitis), so I morphed from a “right-legged” person to a “left-legged” person. The first few years I trained with a one-sided power meter, but then got a Quarq DZero, which measures total power and estimates L/R balance. Initially, it was 55/45, but could dip as low as 58/42. Now it is typically in the range of 50/50–52/48, but could go more lopsided if I am tired.

Thanks for the replies both. I can certainly relate to the ITB pain as being like a knife! I often likened it at the time as a hot poker being pressed into the side of my knee (and I’m pretty sure that it was the RIGHT knee).

I have it in my (not 100% convinced), head that it was the RIGHT shoe that was shimmed, which may align with the comments.

As to why I stopped shimming the shoes, I have no idea! Maybe it was an experiment, maybe something else. It was a long time ago. Curiously, I’ve not had the ITBS issue since then, but the power imbalance has been noticable (albeit only thru data, and not something I particularly “feel”), as is the over/ under definition of vastus medialis…

I think I’m gonna just get some shims 3D printed and experiment anyway!

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If there’s anyone else in a similar position, I’ve just received some 3d printed Keo compatible shims from a guy I found online.

I got an .STL file of Keo profile shim off the web, and sent it over to him. Ordered X2 5mm shims and X2 3mm. They seem spot-on, and cheap @ £2 each (plus postage).

The .STL file can be manipulated to whatever thickness you require.