Background Isokinetic hamstring strength test is considered as a golden standard for identifying players with increased risk of hamstring strain injuries. However, those testing protocols were time consuming and inconvenient.

Objective The aim of this study is to examine the reliability and validity of a novel mobile device based hamstring strength test in soccer players. It is hypothesized that a greater forward flexion angle is associated a greater isokinetic hamstring strength.

Design Cross-sectional study.

Setting A physical test of hamstring strength in clinical setting.

Participants 30 first team players were recruited from professional football clubs.

Main Outcome Measurements In the CUHK hamstring strength test (CUHK test), a smartphone was attached on subject's lower back. Subjects were instructed to lower the upper body from a kneeling position until the point he cannot sustain. Trunk forward flexion angle and angular velocity were recorded by the device. In the isokinetic hamstring strength test, it examined subjects' concentric and eccentric hamstring peak torque. Pearson Correlation, linear regression and intra-class correlation coefficient (ICC) were used to examine the validity and reliability.

Results Result shown that the reliability was good, R=0.845. The CUHK strength test result was highly correlated with isokinetic hamstring peak torque at ecc. 30 degree/second, con. 60 degree/second, con. 240 degree/second respectively, i.e. R=0.81, 0.73 and 0.66. Linear regression analysis shown that the CUHK test was the best to predict isokinetic eccentric hamstring performance at 30 degree/second, R²=0.81, P<.001).

Conclusions CUHK hamstring strength test is a reliable and valid tool to examine athletes' hamstring muscle performance. Clinician and sports coaches may adopt this test for screening and monitoring athletes or patients during rehabilitation or preseason period. Individualized rehabilitation or strength training recommendation could be made based on the test result.