Striving for symmetry

UK fitter and physio Scott Cornish explains why chasing symmetry isn’t always the best approach in fitting.

Asymmetry and malalignment is omnipresent amongst the human population, and I’m no exception. The common notion during my physiotherapy studies was that asymmetry and malalignment (compared to the idealised human symmetry) was bad for performance and the root cause of many of the symptoms of pain and dysfunction, which was carried across in my early bike fit education. ‘Fixing’ it was the focus for improving performance, even if there were no presenting issues of pain or discomfort.

With mixed results from the early days of simply following a process of assessing for asymmetry and malalignment, which is easy to find in anyone, I altered my approach from trying to ‘fix’ these ‘issues’ to assessing and treating for pain-free, efficient function.

Professional cyclists are constantly looking for marginal gains, having their biomechanics regularly assessed and re-assessed for maximal force production and efficiency, whether it's through the use of wedges, foot beds or a strength and conditioning programme (S&C). Current thinking in bike fitting suggests that pedalling symmetry is the ideal scenario. But the key to any intervention is that it is constantly scrutinised in the longterm, checking for any possible positive or negative effects.

For the non-professional cyclist, this constant re-assessment may not always be possible (location, time, cost), hence an approach of seeking efficient function within the acute time frame setting of the fit studio, and a follow-up where possible.

LEVELS OF ASYMMETRY

There are many levels to human asymmetry and it isn’t always the bad guy it’s made out to be, as we can function perfectly well outside of the idealised symmetry and it won't necessarily lead to an increased injury risk.

Asymmetry is typically assessed in a coronal, or frontal, plane, comparing left to right in terms of strength, movement, stability, and — as alluded to — the common assumption is that asymmetry is detrimental to athletic performance, although this is not wholly supported in the research (Malony).

Our organs are not positioned symmetrically and humans often display anthropometric asymmetries, such as different sized ears or feet. We develop unilateral dominance, becoming left or right biased.

Skill dominance is acquired through sporting activities and can be task specific. Adaptive asymmetry in limb strength, stability, left-to-right force production and neuromuscular movement patterns arise between the limbs through unilateral sports such as racket sports, ball sports or sweep rowing. How we sit at a desk or bias one leg when standing, injury and physical conditions all contribute to asymmetry.

This doesn’t just affect muscular tissue either, but also the superficial and deep layers of fascia, our global connective tissue. It encases muscle, nerve fibres, blood vessels and is a major sensory and receptor network within our bodies. It is a fibroelastic, dynamic and omnidirectional tissue, important for its role in posture, movement and performance. It’s a key component when considering human asymmetry as it runs from head to toe and in slings around the body. Its properties mean that it is highly affected by injury, surgery, force production and even factors such as stress.

The common assumption is that asymmetry is detrimental to athletic performance, although this isn't wholly supported in research

THE PELVIS AND LLDS

A stable and level pelvis is a one of the key elements when looking at asymmetry on the bike and can often be missed when looking uniquely at pelvic angle. It can have an affect on the lower kinetic chain and is one of the first aspects I assess on the bike. It can easily be positively affected by postural cues to level out the posterior superior iliac spines. With 36 muscles affecting the pelvis, along with the thoracolumbar fascia and the anterior and posterior fascial slings, any imbalance within these tissues can elicit functional asymmetry in the assumption is that seated, forward flexed position on asymmetry is the bike, when compared to doing an detrimental to assessment in prone lying. This is athletic the reason why I would always performance, perform a thorough physical although this isn’t wholly supported assessment prior to observations on in research the bike - being mindful of any presenting issues, sporting and medical history, looking for any correlations, or not, with movement on the bike, such as a difference in leg length. Leg length discrepancy (LLD) is a common asymmetry in around 90% of the population, with the average difference not being clinically significant (Knutson), and individuals developing compensatory mechanisms for efficient movement. However, there is no consensus of what constitutes a clinically significant difference, with suggestions that it is as much as >20mm (Michalik) — although this relates more to walking and running. Personally, as a physio, anything >5mm and I would consider an intervention, but only once I had established that there exists an actual difference and not a functional one, which is why both a static and dynamic assessment should be made.

We may observe a positive acute mechanical effect, but when an individual has adapted over years to a LLD, it is the long-term effect of function and efficiency that need to be considered, as even a minor height adjustment can trigger an acute negative response in physiological measures of efficiency (MacDermid).

TAKE CARE WHEN SHIMMING FOR LLDS

In prone lying an insignificant difference can be noted (actual), yet as soon as the rider flexes forward on the bicycle, an imbalance in the pelvic associated tissue often produces a functionally significant LLD and an appropriate intervention should be made if this negatively affects the kinetic chain further up, beyond simply adding height under the shoe, as this may lead to long term negative effects. This is an important differentiation to establish, as highlighted by a rider I saw experiencing left hip pain after >1hour riding following a fit session some months prior, where their movement had only been assessed on the bike. A significant LLD was identified and corrected for with two 3mm leg length shims, suggesting a difference of >12mm, as a correction is generally only made for half the difference, due to an already ingrained compensatory mechanisms of the body. A pre-fit, off the bike assessment revealed a non significant difference of around 4mm. Shims were removed over two sessions and an intervention appropriate to the actual nature of the functional difference was made, with strength and conditioning (S&C) exercises and reducing the handlebar reach. This resulted in an actual difference of <5mm, where the rider functions well without any associated pain/discomfort, I would be cautious about intervening with LLD shims, simply due to the compensatory mechanisms in place. If I were to see that rider for regular follow ups during the training and racing season, then it would be a consideration where marginal gains are sought, along with some gym based strength work.

The 'ideal' alignment may never be achieved... improved, long-term function should be the goal

WHEN AND HOW TO WEDGE

Similarly, I do not follow a never be standardised process of achieved… measuring foot varus and then improved, long- fitting x amount of wedges for term function knee alignment. I actually rarely should be the goal. fit varus wedges, instead assessing what is happening further up the kinetic chain from the foot and giving targeted strength and stability exercises, looking for a long term benefit of both muscle activity and physiological efficiency as opposed to an acute benefit in the fit studio. It is all based on the individual, of course, and dependent on how compliant that rider might be with an S&C programme. A single wedge may be fitted alongside the S&C with a view to eventually removing the wedge. The 'ideal' alignment may never be achieved and stacking up wedges may be detrimental in the long term, hence improved, long-term function should be the goal. In the cases of injury or anatomical variations, wedges may of course be required, again with the caveat that S&C is part of the ongoing process of improving function. If we always try to prop up the asymmetry or what is considered malalignment, what then happens to the muscular system that has adapted to the asymmetry or malalignment? That system will likely get weaker. Hence an initial or combined approach of an S&C intervention.

With conditions such as scoliosis, again function should be the goal and not simply following a process to align or ‘fix’ asymmetry. Understanding how a rider with this conditions functions off the bike and any surgical interventions they may have had or ongoing treatment and/or symptoms is key to getting them efficient and comfortable on the bike.

Many riders I see don’t know that asymmetry is really quite normal

INJURIES AND HISTORY

Injury and its lasting effects can often cause asymmetry in movement and force production, a reason why a thorough past medical history should be carried out, to understand what possible limiting physical factors a rider may have. Even wrist and shoulder injuries can affect how a rider holds themselves through the pelvis, through unilateral bracing of the upper limb.

How we approach asymmetries or malalignments that we observe in a session can also have psychological effects on the rider. If you start listing asymmetries that a rider may not be aware of, and how it might affect the body and performance in a negative way, then it could easily negatively affect the rider's mindset, making them worry. It is well known that psychology plays a huge part in performance so care should be taken when describing any findings during a physical evaluation.

Many riders I see don’t know that asymmetry is really quite normal and I will avoid making any negative connotations especially with more recreational riders, focusing on postural awareness at the pelvis and efficient function. For the performance-oriented riders who are more body aware, the approach will be more finetuned, but again not having them worry that their left and right knee movements, for example, aren't perfectly matching. I remember once reading about a pro who had an off the bike ankle injury, and expressed concern that the foot movement was no longer ideally aligned as it was prior to the injury, yet he could still perform.

CONCLUSION

We all live with asymmetry and what asymmetry is really is considered malalignment. Symmetry is considered the holy grail of performance by some, but how much time do most of us have to chase having a symmetrical body? There is only so much that can be done in the brief fit session, and despite what may be observed mechanically, it's the long term gross efficiency in pedalling that required more research. Varus wedging and shimming has its place, but it shouldn't be such a common and systematic approach. Positive, long-term functional results can be achieved through an S&C programme or simply by improving pelvic posture. Asymmetry itself doesn't necessarily lead to injury as there could be numerous contributing factors. The body is complex and every rider can react differently to an intervention, but the goal should be improving function and/or reducing pain or discomfort if present. Addressing asymmetry may be part of that, but it shouldn't be the focus to be 'fixed'.

scott@physiobikefit.com