Validity and Reliability of a Smartphone Application for Assessing Jump Performance from Takeoff and Landing Timing

Purpose: This study examined the agreement and reliability of a smartphone application (JumpEye) for measuring jump outcomes from takeoff and landing timing. Methods: Nineteen recreationally active participants (16 men and 3 women) performed three vertical jumps (VJs) and two five-rebound jump (RJ) trials, recorded concurrently with dual force platforms (1200 Hz) and an iPhone application (240 fps). Two raters analyzed all videos, and one rater repeated the analysis 7 days later. Results: The application underestimated VJ flight time by 2.2 ms and jump height by 0.3 cm. During RJ, it overestimated contact time by 5.4 ms and underestimated flight time by 4.4 ms, jump height by 0.5 cm, and reactive strength index (RSI) by 0.066, with all 95% confidence intervals excluding zero. Intra- and inter-rater reliability were nearly perfect (ICC = 0.997–1.000; CV = 0.15–0.71%). Across intra- and inter-rater comparisons, 77.2–94.1% of takeoff and landing events were identified within the same frame, with all remaining disagreements limited to one frame. Conclusions: The smartphone application provides highly reproducible measurements, although small systematic biases relative to timing-based force-platform values should be considered. Its accessibility may facilitate monitoring of physical function in community and health promotion settings without laboratory equipment.