Biomechanics and Bike Fitting: Leg Length Discrepancy

Biomechanics and Bike Fitting: Leg Length Discrepancy


The Problem

The Bike Fitter’s Solution

The Biomechanics Coach’s Solution

Why Do People Have Different Leg Lengths?

How Can I Fix A Functional LLD?

The Problem

A common problem amongst cyclists is that the pedal stroke feels uneven, one leg feels stronger, the pedal feels closer on one side or whichever way the individual expresses the problem verbally. The root of this feeling is often decided to be that one leg is longer than the other, meaning that either the shorter leg has to overreach or the longer leg doesn’t achieve a full pedal stroke. This Leg Length Discrepancy (LLD) may only be a matter of millimetres, but cycling is a sport of millimetres. The reason for this is that on a bike you are fairly locked into a certain position and doing the same movement pattern over and over – even a short ride of 2 hours will generally use somewhere in the region of 8-10,000 pedal revolutions – and therefore any imperfection in the position will become quickly apparent.

The Bike Fitter’s Solution

The solution to the problem of one leg being longer than the other is generally corrected by bike fitters by putting a shim (a thin piece of plastic or similar) under the sole of the shoe of the short leg, which essentially makes the short leg longer and corrects the problem.

bike fit wedges

This is a great solution from a bike fitting/extrinsic biomechanics (i.e. looking at how the body moves from the outside) point of view and sometimes can be exactly what the individual needs. A less hi-tech solution that can also be used is to lower the seat to the point where the shorter leg is no longer over-reaching, however this is less than ideal as it leaves the body being unevenly loaded on every pedal stroke. Many people would be able to tolerate this for short to medium distances though, and may never realise a problem exists.

The Biomechanics Coach’s Solution

A Biomechanics Coach will always start from the beginning so no matter what the problem is basic function will be checked. In this case, the Biomechanics Coach will not start by seeing one leg longer than the other and go from there looking for solutions. The BC will see one leg longer than the other and ask “Is this leg structurally longer than the other or just functionally longer, and if the latter can it be fixed?”

biomechanics LLD and bike fitting

As you can see from the image above, it is possible to have one leg longer than the other one minute, and reduce or eliminate the Leg Length Discrepancy (LLD) the next. The two images that are side-by-side above were taken 10 seconds apart. If the assumption had been made that the situation in the first picture was permanent, an unnecessary shim of around 3mm would have been added. This client may be able to eliminate the LLD in time once the function in the hip is corrected.

Why Do People Have Different Leg Lengths?

There can be many reasons for an LLD, only a minority are due to the fact that the bones in one leg are actually longer than the other. Most times where this is the case it is due to breaking a leg and the bone not setting in the original position. A more common problem is a rotation of the pelvis (which the legs are obviously connected to) causing one leg to seem shorter than the other. Ideally, every time we lift our leg there should be a small movement of the pelvis which helps the hip joint perform the movement without jamming up. If tightness, spasm or another issue prevents the pelvic movement not only will the leg seem a different length at rest but the movement pattern will be altered, possibly causing issues above or below the hip.

How Can I Fix a Functional LLD?

The good news is that a Biomechanics Coach will have a few tools available to address the issues that commonly cause problems in the pelvis leading to an LLD and often these problems can be completely fixed. Due to the fact that this basic realigning of the body (called the ‘Normalise’ phase in the Biomechanics Coaching system) is the first step in the correction of any problems – see here for an explanation of the basic system – I would always recommend a cyclist looking to feel more comfortable on his or her bike to see a Biomechanics Coach and get normalised before getting a bike fit and addressing the specific problems you have on a bike. If the body doesn’t function off the bike it is highly unlikely to function on the bike, and if apparent issues that are actually only temporary are treated with a permanent solution in a bike fit you may end up feeling less comfortable on the bike or even getting injured.


To arrange a Biomechanics screening, please see the contact page.

For a map of Biomechanics Coaches throughout the country, please see the ‘Find a Coach’ page on the Biomechanics Education site here


Great results with Rugby players in 1st Biomechanics Coaching session

In the last week I’ve done a lot of work with Rugby players of various levels, here are some of the highlights!

– Around 50% of the people got to totally clear on the basic screen within 1 hour, indicating that all basic dysfunctions have been fixed.

– One guy who had problems/pain with his shoulder and failed 4 out of 4 of the shoulder tests ended up passing all the shoulder tests….after 10 minutes of self-releases on his hip!

– Another guy who started with one leg over 10mm longer than the other walked out at the end of the session with no difference in his leg length and much less dysfunction and tightness in the hips.

– A girl who had back pain ended up pain free by the end of the first session, her hamstring flexibility also drastically improved.

These type of results are not out of the ordinary for one hour of Biomechanics Coaching, and unlike most other types of rehab/injury prevention approach you are given the tools to fix the problems yourself. All the above results were achieved without massage, without joint manipulation and without me even touching the person!

The next step on anyone that gets to the stage where they are passing the vast majority of the basic tests is to make sure that the results ‘stick’ and start building stability to support the new alignment of the various joints. The end result is a stronger, faster, pain free athlete who is able to perform consistently and efficiently!

If you are interested in getting a Biomechanics screen, please get in touch via the contact page and you too could be the next to get great results like the ones above.

hoy pendleton cycling biomechanics

Biomechanics are essential, says GB Cycling Performance Director

It was great to hear in the news the other day that the Performance Director of the most successful cycling team that Great Britain has had in recent memory included Biomechanics as one of his fundamental considerations for success!

hoy pendleton cycling biomechanics

Here is an excerpt from the interview:

‘We have a small group led by Chris Boardman who look for the latest innovations in other industries and apply them to cycling.

‘You start by analysing the event that you want to win and then you give yourself priorities because you can’t win everything.

‘We look at the gap between where we are and where we have to be to win and then we create a plan and execute it.

‘If you break down everything that you need and improve every little aspect by 1 per cent then that can make a difference. Some things are essential – fitness, biomechanics, etc – others are less essential but can make the difference such as posture when you sleep, using the right kind of pillow.

‘Hygiene is extremely important because you are going to get ill a little bit less. If you put all these little things together you are going to improve.’

Read more: Londonicle-2184824/London-2012-Olympics-Victoria-Pendleton-event-sad-day–Dave-Brailsford.html#ixzz23AjitMVi

He echoes what I and other Biomechanics Coaches always say – the foundation of any training program, whether it is for a housewife looking to get fit or an olympic athlete going for gold is correct movement first. One should worry about correcting Biomechanics, exercise form etc early in the training/season in order to more safely and effectively perform at higher intensities. Whilst it is certainly possible to reach a high level of sporting achievement with incorrect and inefficient biomechanics, eventually the cumulative effects are premature wear and tear of joints, injuries and performance drop-off.