Purpose The flight-time method (FT) is used for measuring vertical jump height (JH) in the field because of its convenience; however, FT overestimates JH when the lower limb is flexed at landing. Herein, we proposed a new method (ie, flight-time method modified [FTM]) to address the problem of FT and evaluate its validity and reliability. Methods A total of 24 men performed 6 countermovement jumps on force plates (sampling rate: 1000 Hz) while being recorded with a smartphone high-speed camera at 240 frames·s-1. JH was calculated by the impulse-momentum method (IM), FT, and FTM. For FTM, the flight time and JH were calculated based on the displacement of the greater-trochanter marker using a smartphone application. Results JH calculated using FT was significantly higher (P < .001) compared with JH calculated by IM; however, JH calculated by FTM showed no significant difference with JH calculated by IM. Furthermore, JH calculated by FTM, compared with JH calculated by FT (? = .882; 95% CI, .838-.914), exhibited a stronger, nearly perfect, and significantly positive correlation (? = .987; 95% CI, .982-.991) with JH calculated by IM and showed high reliability. Conclusions The FTM proposed in this study had higher concurrent validity compared with FT and a high reliability for measuring countermovement JH because it was not affected by lower-extremity flexion at landing. Therefore, practitioners should consider using FTM as a convenient, low-cost, reliable, and more valid method for measuring JH in the field.
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