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

Background Handheld dynamometry (HHD) has been recommended in return-to-play (RTP) assessments following shoulder injuries; however, variations in testing methods limits interpretation of results. In contrast, isokinetic dynamometry is considered gold-standard for assessment of strength but is less accessible than HHD. Further assessment is needed to identify which shoulder HHD testing positions best reflect isokinetic dynamometry values and can be used to guide RTP practices in adolescent athletes. Purpose To compare HHD strength values of shoulder internal rotators (IR) and external rotators (ER) to isokinetic values in healthy youth athletes. Study Design Cross Sectional Methods Healthy, youth athletes aged 14-18 years with no history of upper extremity musculoskeletal or neuromuscular conditions or injuries in the prior six months were recruited from local teams, clubs, and youth sports organizations. Participants completed strength testing on dominant (DOM) and non-dominant (NON) limbs in three HHD testing positions: prone, seated, and supine. Isokinetic testing (Biodex) was completed seated at 60 degrees/second. Differences between Biodex measures and HHD conditions, as well as between HHD conditions, were evaluated using Wilcoxon signed-rank tests with effect sizes (r) and intraclass correlation coefficients (ICCs). Results A total of 64 participants (37 male; 16.8±1.0 years) participating in primarily football, baseball, lacrosse, volleyball, and basketball were included for analysis. Seated HHD for IR differed from Biodex on both limbs (p<0.001) and from prone on the non-dominant limb (p<0.001). Between HHD positions for the IR’s, seated differed from prone and supine bilaterally (DOM: p<0.001; NON: p<0.001). For the ER’s, HHD measures differed from Biodex in all positions (DOM: p<0.001; NON: p<0.001). Between ER HHD positions, seated differed from prone and supine bilaterally (DOM: p<0.001; NON: p<0.001). Agreement between Biodex and HHD positions was consistently small for ER (DOM: ICCs=0.28-0.43; NON: 0.29-0.38) and was strongest in prone for IR (DOM: ICC=0.81, 95%CI=0.69-0.88; NON: ICC=0.84, 95%CI=0.65-0.92). Conclusion This study demonstrated that HHD shows agreement with isokinetic dynamometry for strength of the shoulder IR’s in adolescent athletes when assessed in prone or supine; however, HHD is poorly correlated with isokinetic strength measures of the ER’s. Level of Evidence 3