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Limb Asymmetry; is my Left supposed to be “more” than my Right?

One of the greatest challenges humans have today isn’t deciding what to pursue, but what not to. There is now an unparalleled amount of data and information at our fingertips thanks to great advances in technology. With such overload, we are all bound to find differences in our data…asymmetries.

Asymmetry is simply the lack of equality or equivalence between parts, a broad and DANGEROUS term that can call to us like sirens.

The first question should NOT be the sheer comparison (L v R), but rather “what does symmetry have to do with health and performance?” Humans are naturally asymmetrical (both in movement and anatomically), and those asymmetries can actually be beneficial at times.

For example, the overall body of research has shown that interlimb asymmetries (left-right) have no consistent relationship with performance. We all have asymmetry, some of the most elite sprinters have shown clear asymmetries upon analysis, (see Usain Bolt) without any clear risk.

Studies that examine the effects of asymmetry on measures of performance are scarce, research has shown that they tend to be task specific. So even if asymmetry had major significance, you would have to test that asymmetry in every single movement…you’d be testing all day, every day.

A 2018 study found asymmetries vary across commonly used strength and jumping-based tests, and that the same side is also rarely favored. That means that the right leg can be dominant in a squat, and the left leg dominant in a jump. Defining and measuring asymmetry while seemingly simple on the surface is much more complex in practice.

With measures of inter-limb asymmetry being so task-specific, it isn’t practical to address each asymmetry in your training plan. Simply said, the body doesn’t work Left/Right, just as it doesn’t work Upper/Lower; it works as a system. Instead of testing for a specific limb capacity or strength, you should holistically assess movement quality as related to health and performance outcomes. Something as simple as balancing on your left leg versus your right evaluates more than leg stability; proprioception, core stability, etc.

True asymmetry is a much broader topic, conceptual asymmetry if you will, a higher level, more meaningful concept. For example, how is your cardiovascular fitness relative to your strength? Your stability relative to your mobility? Finding asymmetry is easy, and Left versus Right just makes so much sense, but they are not the driving factor. After all, there is a reason that a car’s tires cost less than the car’s engine.

Reference

Bishop, C., Read, P., Lake, J., Chavda, S., & Turner, A. (2018). Inter-Limb Asymmetries: Understanding How to Calculate Differences From Bilateral and Unilateral Tests. Strength and Conditioning Journal40(4), 1–6. doi: 10.1519/ssc.0000000000000371