Scapular Dyskinesis, Glenohumeral Internal Rotation, and Pectoralis Minor Length in Male Elite Tennis Players.
Eo Jin Lee, Young Kyun Kim
70.9% of shoulders in 43 elite male tennis players showed scapular dyskinesis, and higher grades tracked with less internal rotation and a shorter pectoralis minor.
Cross-sectional design means this is association, not cause.
Key findings
170.9% of all shoulders showed scapular dyskinesis, with 79.1% on the dominant side and 62.8% on the non-dominant side.
2Internal rotation decreased as dyskinesis grade increased: in the dominant shoulder, from 54.6 degrees (normal) to 36.55 degrees (obvious); in the non-dominant shoulder, from 59.5 degrees to 36.50 degrees.
3Pectoralis minor length (PMI) decreased significantly with increasing dyskinesis grade in both shoulders, with the obvious group showing the shortest values and the largest effect sizes (eta-squared 0.50 dominant, 0.49 non-dominant).
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What it does not show
All participants were male, aged 14 to 24, and played tennis, so the findings cannot be generalised to other sports, other sexes, or older athletes. The cross-sectional design means the associations between dyskinesis grade, internal rotation, and pectoralis minor length cannot be read as causal in either direction. The obvious-dyskinesis subgroup was small (11 dominant, 5 non-dominant shoulders), which limits the precision of the estimates for that group. Injury history and current pain were not collected, so it is unknown whether the dyskinesis and rotation changes were symptomatic or purely adaptive. The lateral scapular slide test, a common static scapular alignment measure, did not differentiate between dyskinesis grades, suggesting it may not capture the dynamic malalignment seen in overhead athletes.
Declared interests
The authors report no conflicts of interest.
The easy way to misread this
Do not read the association between dyskinesis grade and reduced internal rotation as evidence that dyskinesis causes the rotation loss, or that correcting dyskinesis will restore rotation. The study is cross-sectional, the authors state causality cannot be inferred, and the pectoralis minor shortening may be an adaptation to repetitive overhead loading rather than a primary defect.
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