Often our bike fitting work in the clinic gets a curve ball in the form of uneven leg length. This means the reach to the pedals appears different for each leg, throwing the pelvis into asymmetry. Given that my first goal in fitting is a steady, controlled pelvis to provide a solid foundation for the legs, the issue needs to addressed in the appropriate way.
There are two distinct types of leg length difference (LLD).
- Functional, where the difference is not truly in the bones but within muscle or joint asymmetry causing the leg to behave as short
- Real, where there is a genuine difference in bony length and often a mismatched foot size
Because we do a thorough physio exam before getting on the bike I’m aware of what I’m going to see in the cycling form. I’ve already noted it in the physical measurements, stance and walking pattern. The pattern on the bike then confirms what we have already seen. Interestingly the differences often stand out in even greater contrast when in the saddle.
Usually, in standing, the short leg side will:
- have tighter muscles around the front of the hip
- have a foot that looks and fits a little flatter
- have a small trunk shift towards this side, increasing the load on this leg
The long leg side will:
- show a slight knee flexion in stand and have tighter muscles behind the knee
- show subtle weakness in the outer hip stabilizers
Very small differences of functional LLD need nothing more than simple corrective exercises (often it is a tight hip flexor and/or adductors) and an awareness to avoid the postures that accentuate them. On the bike I might advance the short side cleat 1 -2 mm and take the long side cleat back 1-2 mm and note (and encourage) the slight increase in toe down position on the short side that the rider has already figured out helps them feel more balanced. Some riders will tell me straight away though that they do not like this feel of the cleats being staggered whereas others actually prefer it. We work with what helps you feel best on the bike.
A bigger difference or real LLD will mean adding height to the short side cleat stack in the form of shims, effectively making that leg longer and then adjusting the fit at the saddle as needed. This is the preferred option also for those who don’t like the staggered cleat feel.
Because we are dealing with sophisticated neuromotor control systems (your brain!) which will alter muscle patterns, it often takes a little tweaking after the main adjustments to get things to their happy balance point. It is very important to allow time to adapt to the new position which can take a few moderate length and effort rides. Once there though it really doesn’t change and the major obstacle to being more connected to the bike is removed.
Both myself and Jennifer are experienced physiotherapists, bike fitters and cyclists. Visit us at West 4th Physio if you need leg length assessment and an exploration of which variations of compensation will work best for you.