AI Summary
5 min readIn a 2024 study, a single degree of increased ankle range of motion improved elite 8K race times by seven to eight seconds. That is the kind of performance gain hiding in plain sight when you address asymmetries. But the science of muscle imbalances is not simple. A recent review of over 6,000 athletes across 30 studies found that about a third of the research linked asymmetries to more injury, a third found them relevant, and a third said the evidence was inconclusive. Meanwhile, a study of nearly 300 Jamaican sprinters found that symmetry in wrist, ankle, and knee size predicted who was faster in the 100-meter dash—and who was still faster 14 years later. So the central question is not whether asymmetries are good or bad, but when they matter and what to do about them.
The Three Types of Asymmetry
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What you'll learn
- 1 (00:00) **Episode Introduction & The Ankle Asymmetry Example** - Dr. Andy Galpin opens with a striking example: a single degree increase in ankle range of motion can improve race times by 7-8 seconds, setting up the episode's focus on asymmetries.
- 2 (02:28) **The 10% Rule & The Confusion Around Asymmetries** - Galpin introduces the common "10% rule" for acceptable asymmetry, but immediately notes the scientific evidence is mixed.
- 3 (04:39) **The Three Eyes Framework: Investigate, Interpret, Intervene** - Galpin outlines the episode's structure for tackling asymmetries: measurement, interpretation, and correction.
- 4 (06:23) **Three Types of Asymmetries: Morphology, Quality, and Functionality** - Galpin defines the three distinct categories of asymmetry that must be considered separately.
- 5 (11:15) **Skill vs. Force Dominance** - Galpin distinguishes between skill-dominant and force-dominant sides, explaining how they differ by sport (e.g., badminton vs. soccer vs. baseball).
- 6 (13:44) **Why Asymmetries Develop: The Van Valen Model** - Galpin breaks down the causes of asymmetries into four categories: directional (genetic, predictable), anti-symmetries (genetic, unpredictable like handedness), fluctuating (environmental), and repeated movement-induced adaptations (skill development).
- 7 (24:12) **The First Eye: Investigate - How to Measure Asymmetries** - Galpin emphasizes that bad data is worse than no data and outlines best practices for testing.
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Show Notes
In this episode, I tackle muscle asymmetries and imbalances — when the differences between your two sides help you, when they hurt you, and what to actually do about them. I move past the popular "10% rule" and walk through my three I's framework: how to investigate asymmetries across morphology (muscle size and shape), quality (fat infiltration inside the muscle), and functionality (strength, power, and movement); how to interpret the data using context rather than blanket numbers; and how to intervene with a practical five-step correction program built around unilateral training and plyometrics. I cover testing tools from tape measures to MRI, the research on grip-strength asymmetry and aging, and why lower-body asymmetries warrant more attention than upper-body ones. This is for athletes, coaches, and anyone who moves and wants to reduce injury risk or perform at their best.
Sponsors
Momentous: https://livemomentous.com/perform
LMNT: https://drinklmnt.com/perform
David: https://davidprotein.com/perform
Timestamps
(00:00:00) Introduction
(00:02:30) The Three Types: Morphology, Quality, Function
(00:09:09) Laterality: Skill vs. Force Dominance
(00:13:21) Why Asymmetries Develop
(00:19:47) The Bilateral Force Deficit
(00:24:43) Investigate: How to Measure Asymmetries
(00:29:27) Morphology: Tape Measures to MRI
(00:30:41) Tissue Quality & Fat Infiltration
(00:36:21) Functionality: The Unlimited Field of Tests
(00:42:30) Interpret: When Do Asymmetries Matter?
(00:43:25) Muscle Size: Is the Asymmetry Even Real?
(00:51:02) Push vs. Pull & the Limb-Length Myth
(00:58:44) Movement Screens & the FMS
(01:01:30) Strength, Power & Injury Risk
(01:04:25) Grip Strength Asymmetry & Aging
(01:09:46) Symmetrical Sports & the Energy Leak
(01:15:53) Red, Yellow, Green: The Real Thresholds
(01:19:35) Intervene: Correcting Asymmetries
(01:20:46) Why Plyometrics Work Best
(01:23:50) The Five-Step Correction Program
(01:31:59) The Volume Game
(01:33:50) Resources & Final Takeaways
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