ABSTRACT
Abstract Aim: To determine whether the change of direction (COD) deficit can represent the time of the change of direction in professional under 17 years old (U-17) soccer players. Methods: Sixteen young soccer athletes performed the adapted 505 agility test with the stationary stance (2 straight lines of 5 m) and the 10 m linear running test (LR). In both tests, the partial and total times were recorded every 2.5 m by time gates (0-2.5 m; 2.5-7.5 m; 7.5-10 m). The best performances were recorded and used to determine the COD deficit (difference between the time for the LR and 505 tests). The paired t-test compared the initial acceleration (0-2.5 m) time, the COD time (2.5-7.5 m), and the COD deficit among the tests. Results: Times in the LR test were significantly shorter in the initial acceleration phase (0-2.5 m), and the change of direction deficit was also lower than the change of direction time (2.5-7.5 m) for both sides (p = 0.005). Conclusion: When an athlete is aware of an upcoming change of direction, a lower initial acceleration results in biases for determining the change of direction deficit. Therefore, acceleration capacity might not be suitable to assess using the 505 agility test.