Validity and reliability of the portable Kforce plates system with the use of a smartphone application for measuring countermovement jump

Physical fitness is of great importance to several sports and also, in the context of public health. Several training methods such as plyometric jump training are routinely used by athletes for promoting performance. The countermovement jump (CMJ) is one of the most implemented method for testing lower limb mechanical abilities. The purpose of the present study was to examine the validity and reliability of the KForce plates system with the concurrent use of 'My Jump 2' application for measuring CMJ. Is KForce plates system a valid and reliable tool for measuring CMJ? Thirty-four collegiate athletes, twenty-two males and twelve females (age=21.6±5.7), volunteered to participate in the present study. Each participant performed three maximal CMJs while standing on a portable force platform. The jumps were recorded with a portable KForce plates system and a concurrent validated application ‘My Jump 2’ through iPhone 13 at the same time. Each participant repeated the testing procedure after seven days in order to assess the reliability of the measurements (ICC). Systematic bias between sessions and tools was evaluated using paired t-test and Bland-Altman analysis. High test-retest reliability (ICC > 0.87) was observed for all measures (jump height and jump time) in-between conditions. Very large correlations in the sample were observed between KForce plates system and My Jump 2 app for CMJ (jump height, r = 1.000, p = 0.001) and CMJ (jump time, r = 0.999, p = 0.001). The Bland-Altman’s plot illustrates limits of agreement between KForce plates system and My Jump 2 app where the majority of the data are within the 95% CIs. The results of the current study suggest that the KForce plates system was proven a valid and reliable tool for measuring jump performance in physically active adults.