Three articles on PainSci cite Guan 2022: 1. Does Posture Matter? 2. The Complete Guide to Muscle Strains 3. Your Back Is Not Out of Alignment
PainSci commentary on Guan 2022: ?This page is one of thousands in the PainScience.com bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.
“Inter-limb asymmetry” is an alleged asymmetry between the two sides of limbs, such as a difference in strength between the hamstrings and the quads (e.g. the H:Q ratio) — probably the best known example. Supposedly such asymmetries trip us up (perhaps even literally) and cause injuries.
This review of 28 studies is noteworthy in that the studies were of generally high quality — “prospective” studies all — which are required if you’re ever going to get beyond mere correlations. This is not “garbage in” business-as-usual: this data was “garbage” not because it was low quality, but because the problem is just too hard, too messy, too many variables! For instance, these studies were about “lower-limb strength/power, dynamic balance, and muscle flexibility.” And even the same kind of asymmetry can be measured different ways:
Even using the same test, it is difficult to compare the amount of inter-limb asymmetry between studies using different parameters (e.g., jump height vs. peak ground reaction force during landing in unilateral CMJ). The variation in selection of tests may result in inconsistent findings, especially when using the cut-off values for injury prediction.
And then there were also many kinds of people studied, different ways of defining injuries, and more.
And so the paper was conclusively inconclusive. The existing evidence simply cannot clearly tell us anything about the effect of inter-limb asymmetries on injuries. This paper is mostly a resource for researchers designing better studies. But it’s also useful for making the point that it’s not actually possible to know anything about muscle balance based on evidence: we do not have the science.
~ Paul Ingraham
original abstract †Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.
BACKGROUND: Inter-limb asymmetry in lower-limb functional performance has been associated with increased risk of sport injury; however, findings are not always consistent. «Understatement!»
PURPOSE: To conduct a systematic review on whether inter-limb asymmetry in lower-limb functional performance can predict sport injury.
METHODS: Four electronic databases (MEDLINE, EMBASE, Web of Science, and SportDiscus) were systematically searched for prospective cohort studies reporting the association between inter-limb asymmetry in lower-limb functional performance and sport injury.
RESULTS: A total of 28 prospective cohort studies were included in the analyses. Collectively, the findings were highly inconsistent, and a clear statement on the association between each asymmetry and sport injury was difficult.
CONCLUSIONS: Highly inconsistent findings make it difficult to create clear recommendations on the relationship between the inter-limb asymmetry in lower-limb functional performance (power, muscle flexibility, and dynamic balance) and sport injury. The influence of potential factors (selection of tests/parameters, participant characteristics, definition of injury, and ways of calculating asymmetry) should be considered when using previous findings.
This page is part of the PainScience BIBLIOGRAPHY, which contains plain language summaries of thousands of scientific papers & others sources. It’s like a highly specialized blog. A few highlights:
- No long-term effects after a three-week open-label placebo treatment for chronic low back pain: a three-year follow-up of a randomized controlled trial. Kleine-Borgmann 2022 Pain.
- Exercise and education versus saline injections for knee osteoarthritis: a randomised controlled equivalence trial. Bandak 2022 Ann Rheum Dis.
- Association of Lumbar MRI Findings with Current and Future Back Pain in a Population-based Cohort Study. Kasch 2022 Spine (Phila Pa 1976).
- A double-blinded randomised controlled study of the value of sequential intravenous and oral magnesium therapy in patients with chronic low back pain with a neuropathic component. Yousef 2013 Anaesthesia.
- Is Neck Posture Subgroup in Late Adolescence a Risk Factor for Persistent Neck Pain in Young Adults? A Prospective Study. Richards 2021 Phys Ther.