Sporis, G, Vucetic, V, Jovanovic, M, Jukic, I, and Omrcen, D. Reliability and factorial validity of flexibility tests for team sports: Method paper. J Strength Cond Res 25: 1168–1176, 2011. (2011)

To the Editor: We will respond to all the remarks point by point: 1. We are very glad that you have found our article interesting to read and comment. Because of the complexity of the study, it is normal that some clarifications are necessary; the title of the paper was suggested by the reviewer; initially, the title was “Reliability and Factorial Validity of Flexibility Tests for Soccer Players”; also, one reviewer asked us to do the crossvalidation study, and we have made the necessary corrections. Subsequently, we have also changed the title of the article, as suggested by the reviewers. 2. As it was pointed out, there is no or weak evidence that flexibility training is beneficial for injury prevention, muscle soreness, or performance. This is correct because no strong scientific evidence existed to state this claim. But according to my experience as a coach (working with Croatian national team, U-19, U-17, and U-15 and also with many female selections), one of the reasons why soccer is so popular is that players need not have outstanding abilities in all areas (technical, tactical, biomechanical, physiological, and mental), but must have a reasonable level of each of them, thus also a reasonable level of flexibility. For soccer players, dynamic flexibility is indirectly beneficial (2-4), and if we want our players to be efficient in sprinting abilities during the 90 minutes of the game. To be able to achieve this, they need to have an appropriate level of aerobic capacity and also an appropriate level of flexibility (and of all other conditioning abilities). For coaches, this is a normal claim, which is also appropriate for this journal because it implies practical application, not just the pure science, and also the bridging of the gap between science and practice. So, it is to be considered as our assumption, for which we hope to find solid scientific proof in our future studies. 3. To determine the factor validity of new flexibility tests, we have used a previously published methodological model (1). The intercorrelation matrix of 6 flexibility tests was factorized using a principle components factor analysis. The number of significant factors was determined by the Kaiser-Guttman criterion, which retains the principal components with eigenvalues of 1.0 or greater. The structure matrix was used to determine the factor validity. The factorial validity is one form of construct validity and was identified in the test showing the highest correlation with the extracted factor. The confirmatory instead of exploratory factor analysis was used to determine the validity of these 6 flexibility tests to gain an insight into the complex latent structure of flexibility for the tests used in this study (therefore we have used the simplest factor analysis—the principal components analysis with varimax rotation). For the future studies, we need to combine our flexibility test in the analysis with other motor and oxygen-transport-system-related abilities tests to gain a stronger evidence of its validity. 4. In the last remark, we have to agree with the professor. 5. We would like to express our gratitude for reviewing our article and contributing to its quality with your comments. We are going to suggest you as a reviewer in our future studies. The comments that you have given will be taken into account for future publications. Goran Sporis, PhD Vlatko Vucetic, PhD Mario Jovanovic, Bed Igor Jukic, PhD Darija Omrcen, PhD Faculty of Kinesiology, University of Zagreb, Zagreb, Croatia