Static and dynamic strength of the shoulder rotators in healthy, 45- to 75-year-old men and women.

Abstract

Although clinicians routinely treat patients > 45 years of age and use ratio data in making treatment decisions, the reliability of performance of these individuals and the potential utility of ratio data are unclear. The purposes of the present study were to examine the reliability of peak torques and external/internal rotation (ER/IR) ratios for static, dynamic-concentric, and dynamic-eccentric tests and to determine the interrelationships between strength measurements in healthy 45- to 75-year-old subjects. Twenty men and 20 women (mean age = 59 +/- 9 years) were tested on two occasions, completed within 4-6 days. With subjects sitting and their dominant glenohumeral joint positioned in the scapular plane, two isolated contractions were completed at 0, 60, and 120 degrees/sec angular velocities. For peak torques (Nm), all 10 reliability coefficients > or = 0.83, whereas for external rotation/internal rotation (ER/IR) ratios (%), all five reliability coefficients < or = 0.67. Relative measurement error (standard error of measurement/ standard deviation) was much larger for ER/IR ratios (56-79%) than for peak torques (17-41%). Static and dynamic scores were highly related for peak torques (r = 0.72-0.89), but poorly related for ER/IR ratios (r = 0.23-0.36). The high variation associated with ratio data and its tendency not to follow the pattern of relationships which characterizes absolute data suggests that clinicians exercise caution when making treatment-related decisions using ratio data.