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Anthropometric Asymmetry
I often talk about anthropometric asymmetry being one of the main drivers of tissue stress and overuse injury. We as practitioners identify the limb length discrepancy aspect of this in our patients, and we may go through a process of management where appropriate to negate this. Of course, asymmetry is present everywhere in the human musculoskeletal system, but we don’t often look beyond the LLD. Asymmetry can definitely displace the CoM via ascending forces, but this can coexist with descending forces too, as the body adapts to establish the smoothest path during motion.
In this patient, there was a normal magnitude anatomical LLD (left longer), but the main driver for CoM displacement was the asymmetry in his left arm due to congenital hypertrophy/hyperplasia. As a percentage of total body weight, the average adult arm is 5.33%, the whole trunk 54.1% (Plagenhoef et al., 1983).
I have always posited that the upper body has more of an influence on the lower limb in a descending manner than the lower limb has in an ascending manner (no rotten tomatoes please, it’s just an observation!). It just makes sense! Cause and effect. What comes first – gravity or ground reaction forces? Upright bipedal gait evolved along a timeline of complex morphological changes to balance the CoM under the influence of the geophysics, not the other way around. The geophysics came first circa 4.543 billion years ago, and bipedalism a mere blink of the eye on the timeline.
Should we therefore raise our eyes to the pelvis and beyond, and assess for upper body asymmetry that might actually be the original cause of lower limb dysfunction and pain?