Normative values of agonist-antagonist shoulder strength ratios of adults aged 20 to 78 years

Objective: To determine normative values for isometric flexion/extension, abduction/adduction, and external/internal rotation strength ratios about the shoulder and to determine if these ratios are affected by age or gender. Study Design: A cross-sectional study of 120 healthy volunteers (60 men, 60 women) aged 20 to 78 years. Setting: Orthopedic research laboratory. Methods: Flexion and extension strengths were measured isometrically using a Cybex II dynamometer at arm flexion angles of 30°, 60°, and 90°. Abduction and adduction strengths were measured at 30°, 60°, and 90°abduction. Internal and external rotation strengths were measured (1) with the arm abducted 15°and neutral external/internal rotation and (2) with the arm abducted 90°and externally rotated 30°above the transverse plane. Outcome Measures: Isometric strength ratios for flexion/extension, abduction/adduction, and external/internal rotation. Results: No statistically significant differences in agonist/antagonist strength ratios were found between dominant and nondominant sides or between genders. Age was associated with changes in strength ratios for measurements taken with the arm flexed or abducted 90°. Posture was found to affect strength ratios. Conclusions: These data can serve as a normative reference for clinical use.