Strength Testing in the High School-Aged Baseball Athlete: Reliability, Percentage Ratios, and Pain with Throwing

Digital handheld dynamometry (HHD) is widely used to measure strength. However, among youth baseball athletes, it shows inconsistencies in isometric strength measurements, determination of within-limb strength percentage ratios (SPRs), and tracking changes in strength across a season.

To establish intra-tester reliability of isometric HHD strength testing of shoulder and elbow, describe throwing arm strength trends and SPRs across chronological ages, and report throwing with pain after seasonal participation for high school-aged baseball athletes.

Quasi-experimental observational study.

Isometric strength for throwing arm musculature was assessed in 34 male high school-aged baseball athletes using an externally fixated HHD and normalized to throwing arm ulnar length. Assessed muscles included (1) shoulder external and internal rotators (ER & IR) in neutral, (2) elbow flexors and extensors at 90˚ shoulder flexion, and (3) shoulder ER and IR at 90˚ abduction. SPRs were calculated for antagonistic groups: shoulder ER/IR and elbow extensors/flexors. Intra-tester reliability was also analyzed. Throwing-related pain was assessed with the Kerlan-Jobe Orthopaedic Clinic Shoulder and Elbow Score (KJOC) after one baseball season. Intra-tester reliability intraclass correlation coefficient (ICC), standard error of measurement (SEM), and minimal detectable change (MDC₉₅) were determined for each testing position. Descriptive trends were reported for strength, SPRs, and KJOC scores.

Thirty-four high school-aged male baseball athletes (average age 15.7 ±1.2 years) were recruited for this study, and 30 completed all aspects of the study. Intra tester reliability ICC's were .822-.902. The SEM was 3.01-6.47 Newton-Meters (Nm), MDC₉₅ 8.34-18.0 Nm. Mean SPR values for these athletes for shoulder ER/IR in neutral was 64.0%, elbow extensors/flexors 70.1%, and shoulder ER/IR at 90° abduction 69.7%. SPRs showed increasing trends with greater chronological age. Post-season KJOC scores revealed no pain with throwing for all subjects.

Isometric strength assessment using digital HHD is a reliable method to quantify upper extremity strength in high school-aged baseball athletes. Descriptive SPR trends could aid future research on normative values and analysis of throwing with and without pain.

Level 3.