Isokinetic Dynamometry for External and Internal Rotation Shoulder Strength in Youth Athletes: A Scoping Review.
Ian Leahy, Erin Florkiewicz, Mary P Shotwell
PMID 39628773WHAT IT FOUND
Isokinetic testing in youth overhead athletes reveals sport-specific strength imbalances, particularly in internal rotation, but normative values are inconsistent across ages and sports.
Clinicians cannot rely on adult benchmarks for skeletally immature patients, requiring careful interpretation of dynamic strength ratios to guide return-to-sport decisions.
Key findings
01Repetitive overhead sports like volleyball, swimming, and tennis lead to increased internal rotation peak torque in the dominant arm, often resulting in a decreased external-to-internal rotation ratio.
02Age significantly influences strength asymmetry; older youth athletes (mean age 17.6) show higher dominant-arm strength, while younger athletes (mean age 14.6) do not show statistically significant differences between arms.
03There is a lack of normative isokinetic data for very young athletes (under 11 years), despite repetitive throwing beginning as early as 6-7 years of age.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
Only English-language studies were included. No formal quality assessment of the included studies was performed. Significant heterogeneity in testing protocols (positions, speeds, dynamometer types) makes direct comparison between studies difficult. Data is skewed toward volleyball and swimming, with limited information on youth baseball. No studies included participants younger than 11 years, despite early sport specialization.
Declared interests
The authors declare no conflicts of interest.
The easy way to misread this
Do not assume that a lack of strength asymmetry in a young athlete (e.g., under 15 years) indicates normal shoulder function or absence of injury risk. The review shows that asymmetries often develop later in adolescence, and current normative data for skeletally immature athletes is insufficient to establish reliable baselines for all ages.