Isometric Shoulder Testing Using a Forcemeter Is a Reliable Method of Strength Evaluation

Isometric strength testing using a digital dynamometer is reliable for muscle function evaluation. It allows us to objectify manual strength assessment measurement. We tested intra- and inter-observer reliability of a user-friendly efficient digital dynamometer—the Forcemeter—equipped with a computer program to monitor the measurements and to store the data. Abduction, forward flexion, and external and internal rotation of both shoulders were tested three times in 20 healthy volunteers with no record of shoulder trauma. Isometric contracture was recorded in newtons. The first and the third test were carried out by Examiner A (intra-rater reliability); the second test, by Examiner B (inter-rater reliability). Good reliability was shown for intra-class correlation coefficient (ICC) values which mean moderate to high correlations (r = 0.66–0.93) for both examiners. Moderate to high correlations (r = 0.72–0.91) were found for comparisons between the results obtained by Examiner A

Shoulder Range of Motion Measurement Using Inertial Measurement Unit—Validation with a Robot Arm

The invention of inertial measurement units allowed the construction of sensors suitable for human motion tracking that are more affordable than expensive optical motion capture systems, but there are a few factors influencing their accuracy, such as the calibration methods and the fusion algorithms used to translate sensor readings into angles. The main purpose of this study was to test the accuracy of a single RSQ Motion sensor in comparison to a highly precise industrial robot. The secondary objectives were to test how the type of sensor calibration affects its accuracy and whether the time and magnitude of the tested angle have an impact on the sensor’s accuracy. We performed sensor tests for nine repetitions of nine static angles made by the robot arm in eleven series. The chosen robot movements mimicked shoulder movements in a range of motion test (flexion, abduction, and rotation). The RSQ Motion sensor appeared to be very accurate, with a root-mean-square error below 0.15°. Furthermore, we found a moderate-to-strong correlation between the sensor error and the magnitude of the measured angle but only for the sensor calibrated with the gyroscope and accelerometer readings. Although the high accuracy of the RSQ Motion sensors was demonstrated in this paper, they require further study on human subjects and comparisons to the other devices known as the gold standards in orthopedics