Accuracy of the My Jump Lab App for Two Methods of Single-Leg Countermovement Jump Height Assessment

Background/Objectives: The My Jump Lab app can be used to examine inter-limb asymmetry during the countermovement jump (CMJ), both in healthy athletes and in athletes undergoing rehabilitation post-injury. However, the correct assessment of jump height (JH) using this application requires high measurement accuracy, similar to the method of double integration of vertical ground reaction force values. This study aimed to determine the validity and reliability of the My Jump Lab app for estimating jump height (JH) during the single-leg countermovement jump (CMJ). Methods: Twenty-two healthy male adults performed single-leg CMJs for the dominant lower extremity (D) and non-dominant lower extremity (ND). The AMTI force platform and an iPhone 13 smartphone were used. JH during the CMJ was estimated based on the displacement of the jumper’s center of mass (force platform), the jumper’s flight time (smartphone and My Jump Lab), and the flight time of the reflective marker placed on the jumper’s sacrum (smartphone and My Jump Lab-M). Results: The assessment of the concurrent validity showed (1) poor agreement between the My Jump Lab and the force platform for the ND and D (p < 0.001) and (2) moderate (ND) and good (D) agreement between the My Jump Lab-M and the force platform (p < 0.001). Conclusions: The results of the single-leg CMJ height estimation revealed the greater accuracy of the My Jump Lab-M method compared with the My Jump Lab method. However, due to the good agreement between My Jump Lab-M and the gold standard, this new method may not provide an objective assessment of the height in this vertical jump. Therefore, the most accurate method of double integration of vertical ground reaction force values is recommended for the single-leg CMJ test.