Reproducibility analysis of isokinetic strength measurements of shoulder and elbow muscles in subjects with spinal cord injury

In this study we tested the reproducibility for torque measurements of the shoulder musculature in subjects with spinal cord injury (SCI) on an isokinetic dynamometer. Ten subjects with motor and sensory complete SCI (ASIA A) were studied. The subjects were asked to produce maximal torque for flexion/extension in the elbow, adduction/abduction and internal/external rotation in the shoulder. They were recruited four times - twice by two investigators separately - on which occasions three contraction modes (concentric, eccentric and isometric) were tested. The intra class correlations of the shoulder isometric strength were the highest (range: 0.71-0.88). The smallest real differences were lower for the shoulder (range: 5.5-21.4 Nm) in comparison to the elbow measurements (range: 17.3-38.4 Nm) as were the coefficients of variation, 4.4-19.4% and 9.0-21.7%, respetively. This implies that measurements in the elbow were less reproducible than those in the shoulder. The coefficients of variation were higher for the inter- than the intra-tester measurements. This study demonstrates that among the muscles tested the most reproducible strength was obtained during isometric effort of shoulder rotators when these were performed by the same experimenter.