**5. Conclusions**

The physiological and biomechanical parameters calculated by a progressively increasing swimming speed test corresponding to sLT may not be verified during continuous 30 min swimming in sprint and middle-distance swimmers. Swimmers maintaining constant speed corresponding to the second lactate threshold in a long duration 30 min swimming present individualized biomechanical and physiological adjustments that may not reflect the expected responses. In this case, an additional test for verification or a different mathematical model of lactate threshold calculation may be required to provide a valid guidance of training pace. Coaches should be aware that the individual data obtained by a progressively increasing speed test should be examined thoroughly and tested in training practice before planning a training set.

**Author Contributions:** Conceptualization: A.G.T. and G.G.A.; methodology: A.G.T., P.G.B., and G.G.A.; software: G.G.A.; validation: A.G.T. and P.G.B.; formal analysis: P.G.B.; investigation: G.G.A., I.S.N., and I.M.; resources: A.G.T.; data curation: G.G.A.; writing—original draft preparation: G.G.A.; writing—review and editing: A.G.T.; visualization: P.G.B.; supervision: A.G.T.; project administration: A.G.T. 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 swimmers for their participation in the study.

**Conflicts of Interest:** The authors declare no conflict of interest, financial or otherwise.

#### **List of Abbreviations**

