Leg Length Discrepancy: Diagnosis and Implications to Performance.

It was announced that rider Egan Bernal from Team Inneos Grenadier had finally been diagnosed with a leg length discrepancy in October 2020. 

It was during the Tour de France that Egan Bernal appeared to be really suffering, and soon after it then became known that back pain had been the reasoning for such a drop in performance and conceding so much time to his rivals in the race. 

As news came to the fore, it then became known that his back issue has been a problem since before the Tour de France and actually forced Bernal’s retirement from the Criterium du Dauphine and then his subsequent early exit from the Tour de France before Stage 17. 

Confirmation of the issue came from Egan as follows:

“I’m already thinking about next season. It’s a pretty long recovery because basically, the problem I have is that I have one leg longer than the other and that’s caused me to have scoliosis in my spine and a disc in the spine managed to puncture a nerve that supplies the gluteus and goes down to the leg.’’

Of course myself and many others looking from the outside in don’t know what exactly has been happening behind the scenes up until the point of the issue being diagnosed, but needless to say that if a rider has been suffering considerably because of back pain, and a leg length discrepancy (LLD) is then forming the diagnosis at a later period after the rider as been suffering and been forced to abandon at a grand tour, then this does raise a lot of concern and question marks about why did it take so long to diagnose? 

Regardless of the question marks, the most important thing is that Egan will now be able to move forward with treatment and rehabilitation back to form and we hope to see him back as a serious contender at races next season. 

In light of the news regarding Bernal’s diagnosis, then it seemed a good opportunity to provide some background on the subject of Leg Length Discrepancy (LLD) and the implications on cycling performance.

Firstly it is important to outline the two main types of Leg Length Discrepancy:

· FUNCTIONAL Leg Length Discrepancy:  Functional is used to indicate when there is biomechanical asymmetry caused primarily by muscle shortening normally originating from lumbar area of the body, causing a lateral tilt to the pelvis and a subsequent functional leg length difference.

· STRUCTURAL Leg Length Discrepancy: Structural is associated with actual bone length of the lower extremity, for example: femur, tibia. Structural Leg Length can only be diagnosed by orthopedic specialists who will use either x-ray, santogram or CT scan to reach a definite structural diagnosis.

Leg length discrepancies are actually very common.  It is not only an issue that can only be attributed to those involved in cycling or other sports, because it can affect anyone. Many things such as: seated posture, required movements during manual work, posture while winding down of an evening watching television or a movie, can all contribute to creating biomechanical imbalances over a period of time. 

Having worked on many cyclists in bikefit, and also treated many people in a sports therapy capacity which included those from sport and non-sporting backgrounds, I personally found that Leg Length Discrepancies were extremely common, with more than 75% of assessments finding a discrepancy which could range from 2-3mm right up to 12mm and more, depending on other factors.

When taking into account the two types of leg length discrepancies (functional and structural) is it important to outline how the diagnosis can be made, and most importantly, who can make them: 


 As already mentioned, functional discrepancy relates to biomechanical asymmetries which create the appearance of one leg being a different length to the other. Such asymmetries can primarily be attributed to the muscles Quadratus Lumborum (QL) and Hip Flexors, of which all are found within the lumbar area of the back. When the location of these muscles are viewed closely – particularly QL – it is easy to see the influence of the muscle on creating a lateral tilt of the pelvis, thus raising one side which creates a knock on effect to shortening one leg on the same side of the short and/or tight QL.

Who can diagnose?

 Functional leg length discrepancy, postural asymmetry, causes and corrections, can be diagnosed by anyone with formal education and qualifications relating to the body, such as: manual therapist, physiotherapist, osteopath. It is important to note that many bike fitters will have been trained to assess for leg length discrepancy (diagnose the symptom), but will not be qualified to make an advanced diagnosis of the actual cause or corrective process that the body needs to go through – they should always refer the rider to one of the already mentioned specialists. There are some bike fitters who are also trained as specialist therapists therefore they can still make the diagnosis and present the corrective strategy for an individual. An assessment of Leg Length is carried out by comparing the left and right medial malleolus of each leg. Any difference in the height when compared side by side then suggests further investigation is required for any confirmed discrepancy. 

Can it be corrected?

 Under the guidance of one of the specialists mentioned, then yes, as long as a thorough assessment has been carried out, then through the use of treatment in the form of manual therapy, advanced stretching techniques, rehabilitation exercises and strength work, it is possible to correct.  Having already mentioned bike fit, correction of a functional leg length discrepancy will also mean that long term corrective leg length shims should not be needed if correction has been achieved via the means and specialists mentioned above. Correction of the root cause of a functional discrepancy is a much better longer term outcome than simply treating the symptom ie. using a leg length shim, as seen below:


Bone length leg length discrepancies do exist but are less common than functional discrepancies Over the years of working in bike fit and the treatment of cyclists and others, I can honestly say there are not more than 4 – 5 people who I have worked with or treated who have had a confirmed bone length issue. Generally, those with a bone length discrepancy will have had it previously confirmed by a specialist, or there will have been a serious event that they recall, such as an accident usually in the form of a severe leg break whereby the person will be aware of the long term outcome. If there has been no major trauma then often the bone length discrepancy can simply be attributed to growth. 

Who can diagnose?

The only specialists who can give the final confirmed diagnosis of bone length causing a leg length discrepancy, are orthopedic specialists.  Others, such as therapists, physiotherapists and osteopaths are of course qualified to raise the question of bone length during an assessment if it is clear that there is a discrepancy found during assessment and comparison of bone landmarks, but this is when a referral must be made for further evaluation and confirmation from the orthopedic specialist who will use either x-ray, santogram or CT scan to reach a definite structural diagnosis. 

Can it be corrected? 

If there has been a definitive diagnosis of a bone length discrepency from an orthepedic specialist, then correction will most likely involve cleat shims to correct a shorter leg for cyclists, or in the form of a specialist insole that has a corrective stack to assist with the difference in leg length. Shim and insole stacks should be carefully calculated for the exact depth needed to assist with the confirmed difference.   For cyclists, it is imperative to work closely with a bike fitter who understands the corrective measures of shims in order that your position can be dialed in exactly using this corrective measure. Also, if shims or insoles are used then often there is a period whereby the rider needs to adapt to the corrective measure – no different to any bike fit – but often when a rider gets re-aligned and balanced on the bike due to a good bikefit, they can often feel very misaligned after correction because of course their body has grown to think of the old position as normal. So the bike fitter should be able to guide on the process and recommendations to retrain the body in the immediate weeks after such a correction.  A follow up with the bike fitter after a period of adaptation is highly recommended. 

With regards to correcting the bone length: there are surgical procedures to perform ‘Limb Lengthening’ but these are highly invasive and general reserved for those with significant discrepancies in length. Such a procedure will normally involve a ‘external fixation system’ which is a scaffold-like frame that is connected to the bone with wires, pins, or both (seen below). By turning dials on the fixator several times a day, the bone may lengthen 1 mm per day, or approximately 1 inch per month. Overall, a long, invasive and painful correction.

What are some of the common signs and symptoms that may indicate further investigation is needed for potential leg length discrepancy?

– Over sensitive / tight glutes on one side (a longer leg). 

– Under active / Weak glutes on the shorter leg due to over extension of the (shorter) leg during pedal stroke.

– Sciatic impulses and pain on one side of the lower body (glutes) and down the back of leg. 

– Numbness in one foot – mostly the toes on one side due to extension of reach on the shorter side.

– Muscle mass difference in one leg compared to other (particularly quadriceps).

– Tight calf muscles of the shorter leg due to extension to reach bottom of the pedal stroke. 

– Rider feeling stronger more connected on one leg to the other. 

– Ankle more open and toes pointed down on one side. 

– Power meter data showing above normal discrepancy in left & right power readings.

– Saddle wear on one side, also on material of shorts. 

– A lean of the saddle to one side having been bent /mis-shapen over a period of time, suggesting more weight on one side to the other.


Leg Length Discrepancy is extremely common in most people. A functional difference of 2-5 mm is considered to be normal. But of course seeking clarification from a specialist is always highly recommended. 

If any difference is discovered during a bikefit session, then I personally prefer to prescribe stretches for the target muscles (QL & Hip Flexors) and recommend that the rider seek some manual therapy treatment prior to any kind of shim / cleat spacer be inserted to make up any difference of LLD. Such a rehabilitation approach is much better for a longer term correction of the cause rather than the shim/spacer being inserted to treat the symptom, thus leaving the cause untreated and of course, uncorrected. 

Once a diagnosis has been made and a subsequent correction plan has been implemented, it is also important to consider very close attention to re-training seated on the saddle. As mentioned previously, often during the correction phase, the body can feel wrong and uncomfortable even though the correction means the rider is positioned perfectly on the saddle and pedaling much more balanced.  So time should be spent at low intensity to allow the body to become accustomed to the new position. Often the re-centering of the rider on the saddle is the most difficult thing to do as part of adaptation, so a good tip that was passed onto me, is to tape an object on the middle of the back of the saddle so that it gently presses against the centre of the rider’s shorts, and this becomes a central reference point for the rider to confirm if they are correctly aligned in the saddle or not.

Once all correction has taken place and the rehabilitation and strength work has formed the framework of adaptation, then the increase to performance with no resulting pain should be much enjoyed by the rider.