Over the past 15 years of performing professional bicycle fits we have had numerous cyclists visit us and inform us that they have a leg length discrepancy (LLD). There is a great deal of controversy around this topic as some people are proponents of compensating for this variability in leg length and others who are opposed to it. We do not feel there is one “right” answer as to whether you should shim but in this multi article break down we will provide you with the facts and information that we currently have and let you make your decision as to what you think and how your bike fit may or may not be impacted by your leg length discrepancy.
The first place to begin is with the diagnosis of this LLD. Whether you had a fit specialist, massage therapist, chiropractor, physical therapist, general practitioner, or an orthopedist tell you this can make a significant difference in the way your assessment occurred and what that information means for your fitment. Ultimately, the most important part is not who the diagnosis came from, but how the diagnosis was attained. There are three common forms of measurements that we will analyze including visual assessment, physical measurement and x-ray
Visual assessment is often performed on a massage table or similar surface. In this assessment the evaluator will usually manually manipulate the athlete to square their body on the table. This assessment is a visual comparison of foot and heel placement relative to a fixed landmark. Out of the three forms of assessment this has the greatest level of inaccuracy as it is an estimation of a brief visual overview.
Physical assessment is the measurement of the length of the bones based on commonly known physical landmarks of the bones. This assessment provides more well-defined detail than the visual assessment but can frequently exclude the individual’s asymmetry in bodily landmarks, not to mention the variability in assessor’s accuracy.
X-Ray is by far the most accurate method for measuring a structural leg length discrepancy. This method provides the clearest view of an individual’s skeletal structure but can still have slight inaccuracy dependent upon the athlete’s position on the table and variability in cartilage when seated vs standing.
In coming articles we will go into greater detail of the potential reasons for a LLD and considerations that need to be taken in order to make the most accurate decision for your personal riding style and potential physical limitations.