Construct validity and test-retest reliability of the Modified Agility T-Test in healthy adults

Abstract

Background After a lower limb injury, adequate agility is decisive for safe direction changes and reduces the risk of re-injury upon return to sports. Experts recommend that patients should pass standardized return to sports testing which involves agility tests such as the Modified Agility T-Test. Aim Since the quality criteria of the Modified Agility T-Test have not been conclusively clarified, the objective of this study was to evaluate the construct validity and test-retest reliability of the Modified Agility T-Test. Methods The study was conducted as a single-center study in a cross-sectional design comparing the performance of the Modified Agility T-Test with the Illinois Agility Test to evaluate the construct validity of the Modified Agility T-Test. The construct validity was calculated with the Pearson’s correlation coefficient. Absolute and relative reliability were calculated based on the test-retest results. Each participant performed two counting trials of both agility tests. To determine the absolute test-retest reliability, the standard error of measurement, 95 % limits of agreement and the smallest detectable change were calculated. To determine the relative test-retest reliability, the intraclass correlation coefficient 2.1 was calculated. Results A total of 30 participants were recruited, with equal sex distribution and a mean age of 25.7 years. Our results showed a high construct validity of the Modified Agility T-Test (r = 0.89). The absolute test-retest reliability of the Modified Agility T-Test was 0.18 (-0.38–0.62) seconds, whereas the smallest detectable change was calculated to be 0.71 seconds. The relative test-retest reliability amounted to 0.84 (ICC 2.1). Conclusions Our findings support the construct validity and test-retest reliability of the Modified Agility T-Test as an agility test. Thus, it could be used as an alternative to the Illinois Agility Test, particularly in sports which require sideways or backwards movements and for sports with short or rapid displacements.