A Validity and Reliability Study of the K-Muscle Controller Hand-Held Dynamometer in Measuring Shoulder’s Internal and External Rotation Force

<b>Purpose:</b> To evaluate the validity and reliability of a new Hand-Held dynamometer, K-Muscle Controller, compared to MicroFET2 on measuring the shoulder's external and internal rotation strength on patients with shoulder impingement syndrome (SIS). <b>Study sample:</b> A group of 22 (Group A) and a group of 25 (Group B) SIS patients participated. <b>Data collection and Analysis:</b> The isometric force of shoulder internal and external rotation was measured using only K-Muscle Controller (group A, two measurements with K-Muscle Controller) or both instruments (group B, one measurement with each instrument). The Intra-Class Correlation (ICC) test was used to investigate the reliability and validity of the K-Muscle Controller. The Coefficient of Variation (CoV) was also calculated for both shoulders' internal and external rotation of both groups. Furthermore, Bland-Altman plots were used to present the level of agreement between the measurements for both groups. <b>Results:</b> Intraclass correlation tests revealed high correlation coefficients for validity (ICCs ranging from 0.957 to 0.986) and for reliability (ICCs ranging from 0.944 to 0.986) for both groups and both arms for K-Muscle Controller. Moreover, CoV showcased values ranging from 31.77% up to 48.57%. Bland-Altman plots showed that data were within the limits of agreement indicating strong relationship between measurements without any observed trend. <b>Conclusions:</b> K-Muscle Controller was deemed reliable for measuring the shoulder's external and internal strength in both healthy and pathological shoulders.