Shoulder Internal and External Rotator Strength Reliability and Validity in Healthy Adolescent Athletes.

Sixty-four healthy adolescent athletes (14–18 years, 37 male) in contact or overhead sports had shoulder internal and external rotator strength measured bilaterally. Each arm was tested with a handheld dynamometer in three positions (prone at 90° abduction, seated at 90° abduction/90° external rotation, supine at 90° abduction) and with a Biodex isokinetic dynamometer (seated, 45° abduction in the scapular plane, 60°/s). HHD force in pounds was converted to estimated joint torque using sex-specific forearm lever-arm lengths (0.29 m male, 0.25 m female). The best trial per condition was analysed. Comparisons used Wilcoxon signed-rank tests with a Bonferroni-adjusted threshold (α = 0.008); agreement was assessed with ICCs, and measurement error with SEM and MDC95.

Internal rotators: HHD in the prone and supine positions were not significantly different from Biodex, while seated HHD was significantly lower (p < 0.001). Agreement was moderate-to-strong for prone (ICC 0.81–0.84) and supine (ICC 0.76), and moderate for seated (ICC 0.59). External rotators: HHD was significantly higher than Biodex in all three positions (p < 0.001, r = 0.48–0.87), and agreement was consistently poor (ICC 0.28–0.43 dominant, 0.29–0.38 non-dominant). MDC95 for IR in the prone position was 18.3 Nm (dominant) and 16.7 Nm (non-dominant); for seated it was 26.6–26.7 Nm. Reliability was similar across dominant and non-dominant limbs.

If you are assessing a teen athlete's shoulder strength for return-to-play or rehabilitation progression, a handheld dynamometer in the prone or supine position is a reasonable substitute for isokinetic testing of internal rotator strength. However, do not rely on HHD for external rotator strength: the numbers were consistently higher than Biodex and showed poor agreement (ICC 0.28–0.43) in every position. For overhead athletes where ER strength is the concern (rotator cuff, labral pathology), isokinetic dynamometry is the appropriate tool. When tracking IR progress with HHD, a change must exceed roughly 18 Nm (prone position) to be a real change rather than measurement noise.

Only healthy athletes were tested; the study says nothing about how these measurements behave in a post-injury or post-surgical shoulder. HHD was performed without a fixation strap (examiner-held), so results may not generalise to settings that use a belt or strap. Biodex testing was at a single velocity (60°/s) and a different joint angle (45° abduction) than the HHD positions (90° abduction), so the two devices were not measuring the exact same mechanical task. All testing occurred in one session; test-retest reliability of the HHD positions was not evaluated. Single-site study with 64 participants; no blinding of the examiner to condition is described.

The authors report no potential conflicts of interest in the development or publication of the article.

Do not read the overall conclusion as 'HHD is a fine alternative to isokinetic testing for shoulder strength in teen athletes.' That is only true for internal rotators. For external rotators, the muscle group most linked to throwing-injury risk in this population, HHD agreement with Biodex was poor (ICC 0.28–0.43) in every position, and HHD values were consistently higher than Biodex. Using an HHD ER number to decide whether a young overhead athlete is ready to return to sport risks both over- and under-estimating true strength.