This article will seek to describe a relatively common assymetry that I see in about 10% of my clients. The degree of variation is huge, with some of them having a mild assymetry and some having a severe degree of left-right imbalance. The basic premise is the same – many people have two hip sockets which are orientated differently on each side of their pelvis. This variation appears to be a genetic one, with most of these people having no reported signs of major trauma or damage to either hip.
To explain – most of us will have two hips with fairly similar degrees of internal and external rotation available at various hip angles. A normal range of hip motion would be around 60 degrees of external rotation and 30 degrees of internal rotation for example (measured with the hip flexed at 90 degrees). It is not uncommon to see a rider present with a strange assymetry on the bike which will manifest in one of many different ways, but is caused by having more internal rotation on one leg, and less on the other, with a corresponding decrease or increase in external rotation. The rider will present with the same overall range of motion of, say, 90 degrees (60deg external and 30deg internal) but it will be orientated differently (perhaps 45 deg internal and 45deg external).
What this means is that it is not uncommon to have one hip socket which is positioned differently in the ilium but is otherwise identical.
The implications of such assymetries can be minimal or major. The logical mechanical fallout is that one hip’s neutral plane of motion on a bike will be in more external or internal rotation than the other side. This means, all else functioning as it should, that one foot will sit in more external rotation (heel in) on the pedal than the other. The rider’s foot angle will appear assymetrical as they ride, but their knees will track normally and their pelvis will sit square on the bike. The bike fitter may often be tearing their hair out trying to figure out why the foot angles are not symmetrical thinking there is a problem, but there is no underlying problem at all.
If the cleats have been fitted on the same angle on the shoe, and the float is blocking one or both feet from rotating to match the hip’s preferred plane of motion, there will be a compensatory movement pattern employed by the rider’s hips/knees/pelvis to varying degrees. It is crucial to identify this assymetry in the pelvis before attempting to fit the rider to the bike, so that each cleat can be rotated differently on the shoe to allow the foot to sit on whatever angle the hip joint dictates. The fallout is often knee or hip pain if this is not taken care of early on in the fitting process.
It should be noted that if the rider has been functioning in a sub-optimal position with assymetrical hip sockets for a long time, they will undoubtedly have other physical signs of it. The most common is a large callus formation (thickened patch of skin) on the base of one big toe, and not on the other. This stems from toeing off assmetrically during gait and when running, loading one of their first rays more heavily than the other. This will be apparently also if the clients has a leg length difference or large pelvic tilt. You can learn a lot about a person by looking at the callus patterns on their feet!
Riders who have been functioning for a long time with a poor position and assymetrical hip sockets will often have a sticky, torsioned SIJ on one side (see part 2 above). This stems from one hip joint having it’s plane of motion challenged, and a compensatory build-up of strength and deep trigger point formations in the hip musculature causing the SIJ to lose anterior rotation. Always check that your client’s SIJ’s are moving freely when assessing this type of thing as a torsioned SIJ can look virtually identical to a pair of assymetrical hip sockets!