BACKGROUND:Confirming the reliability and validity of the My jump 2 application for measuring lower limb vertical stiffness may offer the possibility of it as an alternative to the Kistler three-dimensional force platform for measuring lower limb stiffness. OBJECTIVE:To verify the reliability and validity of the My Jump 2 application in measuring lower limb vertical stiffness of college students. METHODS:The drop jump data of the participants were collected through the Kistler three-dimensional force platform and the My Jump 2 application,and the vertical stiffness of the participants'lower limb vertical stiffness was calculated.The intraclass correlation coefficient was used to analyze the data measured by the My Jump 2 application and the Kistler three-dimensional force platform,attempting to verify the reliability of the My Jump 2 application.The bias and average between the two devices were drawn into a Bland-Altman diagram to verify the consistency between the two test methods.Finally,the test-retest reliability of the My Jump 2 applications at 30 cm and 40 cm was analyzed using the Cronbach's alpha(α)and coefficient of variation.Pearson product-moment correlation was used to analyze the correlation of My Jump 2 applications. RESULTS AND CONCLUSION:My Jump 2 application has high reliability and validity when measuring the vertical stiffness of the lower limb.At the same time,due to its advantages of low cost,convenient portability and field testing for large samples,it can be used as an alternative to the Kistler three-dimensional force platform to test the vertical stiffness of the lower limb in college students and similar populations.

Objective To explore the effect of 6-week high-intensity interval training(HIIT)on health physical fitness of naval officers and soldiers.Methods Twenty male naval officers and soldiers were divided into experimental group and control group according to the random numer table,with 10 cases in each group.The experimental group participated in HIIT 3 times a week for 6 consecutive weeks,while the control group received routine physical fitness training.The physical fitness indexes,such as body fat percentage,plank,sit-and-reach,300-yard(1 yard≈0.914 m)shuttle run,grip strength,standing long jump and deep jump,were tested before and after training.Results Compared with before intervention,there were significant differences in body fat percentage(P=0.009),plank(P=0.003),300-yard shuttle run(P=0.014),sit-and-reach(P=0.05)and right hand grip strength(P=0.005)in the experimental group after intervention,and there were significant differences only in the plank(P=0.042)and standing long jump(P=0.041)in the control group.There were significant differences in the body fat percentage(P=0.016),plank(P=0.001),300-yard shuttle run(P=0.021),sit-and-reach(P=0.003),left hand grip strength(P=0.025)and right hand grip strength(P=0.001)between the two groups after intervention.Conclusion Six-week HIIT can enhance the health physical fitness in naval crews.