Would love to see any evidence that the fitter from the video can actually eyeball a 2mm difference like he claims.
Heās not saying he can eyeball the 2 mm difference. He would measure that in the evaluation at the start. He is saying he can eyeball the rider compensating for the difference: dropping a hip, pointing the toes on one side, a āhitchā in the knee movement.
Iāll admit that I can never see the knee hitch thing he and James talk about, but if you view someone from the back you can see hip movement quite easily.
Unfortunately, the only way to see that on yourself is to take a video. I was surprised just how much I was bouncing on the bike when I watched my recording.
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Fair call, I was a bit snarky in my initial reply sorry. I watched the video again, and as you say he claims to see the change resulting from a 2-3mm difference.
Unfortunately measurement of leg length discrepancies is quite difficult to do accurately/reliably: Leg length discrepancy: A systematic review on the validity and reliability of clinical assessments and imaging diagnostics used in clinical practice - PMC Unless he is using bone imaging of some sort I doubt he is accurately measuring the minute LLD he is claiming to be seeing the effects of.
Iām not questioning whether he can make some people feel more comfortable by shimming one cleat by 2-3mm. The problem is people like him:
- Make claims about what they can see and measure that probably arenāt true
- Overstate the importance of the things they see and measure, ie in this case that (essentially) all cyclists need to have a 2-3mm LLD corrected with shims
The evidence (that I can find) is far less specific than this, eg:
- The Retul system more or less works for non-injury pain, comfort and fatigue: Long-Term Effects of a Kinematic Bikefitting Method on Pain, Comfort, and Fatigue: A Prospective Cohort Study - PMC Reference ranges for joint angles are provided, but they are about 10 degrees for most angles (ie. a lot of leeway)
- Correcting LLD with shims: https://openventio.org/wp-content/uploads/An-Integrated-Analysis-of-Leg-Length-Differences-and-the-Effect-of-Correctional-Techniques-on-Stroke-Mechanics-and-Performance-Indicators-in-Competitive-Cyclists-SEMOJ-1-103.pdf It corrects torque imbalance but there was no increase in power output and efficiency was reduced (at least in the short term, no long term data available)
- Knee pain in cycling: Potential factors associated with knee pain in cyclists: a systematic review - PMC Frontal plane motion is associated with knee pain, but thereās no evidence (yet?) that pain can be fixed or prevented by changing frontal plane motion
(Not defending MVF here - it clearly hasnāt worked for numerous people in this thread, and Iām glad you found a fit youāre happy with)
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I found that I only got good results once I used a tripod to keep the camera in the exact same spot. And make sure itās at saddle height and not tilted at all. Before that it would be inconsistent.
I found it gets me pretty much in the ballpark for saddle height and reach. Have had to adjust my saddle a little bit more forward but thatās it.
Yup. I did that. One time I got wacky results and realized it was because I accidentally recorded with the wide camera, which makes the video a bit fish eyed, so that makes sense. Other than that the results were consistent to themselves. If it asked me to make an adjustment in one direction and I did, the resulting angles moved in the direction they wanted.
I just think the ranges they wanted the angles, and where they defined āgood enoughā was not working well for me. I found in some areas (related to saddle height and setback) I needed to be much closer to optimal than they suggested. In other areas, like shoulder angle, I am more comfortable outside their range.
Iām honestly confused on what you donāt like if people coming to get more comfortable are leaving more comfortable. They got what they payed for.
Also, the vast majority of people are in fact asymmetric:
Many human body parts undergo development with bilateral symmetry. This implies that the right and left sides can be divided into identical mirror images. However, due to biological factors inherent to processes of development as well as environmental disturbances, perfect bilateral symmetry is rarely found.
In normal life, such asymmetries donāt cause any functional problems. However, as Neil points out cycling is a very unnatural activity in that we fix our feet to pedals that are moving in one plane only and repeat that exact motion many, many times. By contrast during walking our feet, legs and hips move a lot more and vary their motion in multiple planes and so can more easily compensate without injury.
It corrects torque imbalance but there was no increase in power output and efficiency was reduced (at least in the short term, no long term data available)
I would expect to see reduced power output (short term) in some more extreme cases because after fixing a problem the muscles will be used in different proportions than before. They muscles as neurons have been trained on the old position. It sound take weeks to months to fully realize the potential of a new position if itās correcting significant compensation.
Also, the point of a fit is comfort and avoiding pain, not increased power, so itās not even the right metric. Itās just easier to measure. But anecdotally, thereās a reason bike fitting is popular. Being comfortable is necessary to have good power, at least long term.
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I have no dislike for that at all. If someoneās happy with their individual outcome, great!
The problem is:
- Health or fitness professionals overstating their abilities, and implying that any person or system that doesnāt have their abilities isnāt good enough.
- Their clients (or Youtube viewers) then believing that is required for every individual.
I believe there should be a more honest relationship between professional and client - and between influencer and Youtube audience.
Yes! But until thereās evidence supporting that this both A: causes a problem, and B: correcting it prevents or fixes the problem, I think we should view with suspicion anyone acting as if A+B are universally true - especially when thereās a financial motive. (If this evidence has been published I apologise!! I couldnāt find it)
Thereās some really interesting discussions on recent Escape Collective - Performance Process episodes with different people discussing their philosophies (no data 
) on bike fit, including optimising for both comfort and power. As you say, comfort is necessary for power long term, and short term studies donāt provide data on long term outcomes.
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But thatās just it. The evidence is that good fitters are using shims and clients are satisfied that it improved their comfort. If the fitter is right or wrong about the why behind it I donāt care.
But also wonder why you donāt believe the leg length theory. Have you ever had a fit before? I had a Retul fit and the fitter did basic things like visually compare the height of my patellas, tibias, etc. They did the same for me in physical therapy.
Do you need a micrometer to tell if two pipes are the same length? Of course not, you can align the ends and use your eyes. And from there itās basic logic that matching length improves mechanics on a symmetric machine.
If we were talking running for example, I would question if ending leg length is beneficial. But on the bike it makes perfect sense. I donāt need a study to prove that. N=1, getting yourself fit, and seeing if it helps you out is all the proof needed.