Reliability and validity of measuring scapular upward rotation using an electrical inclinometer

The aim of this study was to assess the reliability and validity of a modified two-dimensional electrical inclinometer to measure scapular upward rotation during static humeral elevation. Numerous techniques have been proposed to qualitatively and quantitatively measure upward rotation of the scapula. These techniques are limited by expense or an inability to be synchronized with other measurements, such as muscle activity and force output. For validity testing, static scapular upward rotation was measured separately with a digital protractor and electrical inclinometer while participants were at rest and 60°, 90° and 120° of humeral elevation in the scapular plane. For reliability testing, either 20 min before or 20 min after validity testing, participants performed the testing positions while measurements were taken with the electrical inclinometer only. Significant correlations existed between the modified electrical inclinometer and digital protractor at all four positions (r > 0.996, p < 0.001). The electrical inclinometer demonstrated good to excellent intra-rater reliability (ICC3,1 > 0.892, 95% CI: 0.785-0.988 and SEM < 1.8°). These results support the use of the electrical inclinometer to measure scapular upward rotation. These findings provide clinicians and researchers with a practical instrument that can accurately measure scapular upward rotation in synchrony with other measurements, such as electromyography and isokinetic data.