**5. Conclusions**

Although the implementation of 3 × 10 m sprints, either BwR or FwR, to a warm-up does not enhance 20 m sprint speed in recreationally active preadolescent boys, after a recovery period of 4 min, the positive effect of BwR on sprint speed during the distance 10–20 m suggests that BwR might be an alternative means for enhancing performance in certain phases of a sprint speed. However, preadolescent boys' response to different sprint conditioning exercises, optimal rest time and/or conditioning stimuli remains to be determined on an individual basis, taking into account the basic characteristics and limitations of children's physiology.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2075-4663/8/4/55/s1, Table S1: Speed and RPE Values of All Participants.

**Author Contributions:** Conceptualization, D.P. and E.B.; Methodology, D.P., E.B., A.P. and D.A.P.; Validation, E.B., A.X and D.A.P.; Data curation, D.P., E.B. and A.P.; Formal analysis, E.B. and D.A.P.; Investigation, D.P., E.B. and A.P.; Visualization, D.A.P.; Writing—original draft, D.P., E.B., and D.A.P.; Writing—review & editing, D.P., E.B., A.P., A.X. and D.A.P.; Supervision, E.B.. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors would like to thank the participants and their parents for their dedicated time and collaboration.

**Conflicts of Interest:** The authors have no conflict of interest to declare.
