Concurrent validity of the portable gFlight system compared to a force plate to measure jump performance variables

Objective: Lower-limb strength and power is commonly assessed indirectly by measuring jump performance. A novel portable system (gFlight) that can be used in applied settings provides measures of jump performance. The aim of this study was to validate jump performance measures provided by the gFlight to those provided by a force plate. Approach: Thirty-six participants performed three countermovement jump (CMJ) and drop jump (DJ) trials. Jump height (JH), contact time (CT), and reactive strength index (RSI) were simultaneously recorded by a force plate and gFlight sensors to assess concurrent validity. Main Results: Significantly higher measures of JH during the CMJ (Mean: +8.79 ± 4.16 cm, 95% CI: +7.68 to 9.90 cm, P<0.001) and DJ (Mean: +4.68 ± 3.57 cm, 95% CI: +3.73 to 5.63 cm, P<0.001) were provided by the gFlight sensors compared to the force plate. The gFlight sensors displayed significantly higher measures of RSI (Mean: +0.48 ± 0.39 m·s -1, 95% CI: +0.37 to 0.58 m·s -1, P<0.001) and lower measures of CT (Mean: -0.036 ± 0.028 s, 95% CI: -0.044 to -0.029 s, P<0.001) during the DJ compared to the force plate. The bias displayed by the gFlight for JH, CT and RSI measures are eliminated using corrective equations. Significance: The gFlight sensors are a cost-effective, portable measurement system with high concurrent and ecological validity for the objective measurement of jump performance in applied settings. Corrective equations should be used to eliminate measurement biases displayed so comparisons can be made to force plate measurements of jump performance.