**5. Conclusions**

The present study showed that the knee joint adapted to the fatigue state with an increase in knee abduction/valgus, with the e ffect being stronger with wide skis. Furthermore, the balance also deteriorated with fatigue using either ski width. The balance-hampering e ffect was more pronounced with the narrow skis. However, the stability parameters that were shown to be worse even before fatigue in connection with the wide skis compared to the narrow ones further deteriorated in the fatigue state and remained worse compared to the narrow skis throughout all after fatigue experiments. The study elucidates the fact that fatigue is an injury risk factor in skiing [6,7] from an additional point of view and exposes the further risk of using skis with a large waist-width, especially on hard frozen surfaces, as simulated in the study. Considering fatigue and ski waist-width related to balance deterioration, it is obvious that the injury risk for the whole body and not only the knee joint can be compromised. More specifically, the possible mechanisms of acute and chronic knee-joint injury were suggested. The medial collateral ligament tension and the uneven joint pressure distribution while turning in the fatigue state are potential biomechanical injury risk factors. Consequently, apart from using skis with a narrower waist-width, it might also be suggested to regularly interrupt "long" skiing runs/descents with long enough breaks to decrease the risk of injury.

**Author Contributions:** Conceptualization, M.S. and N.Š.; methodology, K.H.; formal analysis, K.H.; resources, M.S. and N.Š.; data curation, K.H. and M.Z.; writing—original draft preparation, M.Z. and K.H.; writing—review and editing, M.S., N.Š., and M.Z; visualization, M.Z. and M.S.; supervision, M.S. and N.Š.; project administration, N.Š. and M.S.; funding acquisition, N.Š. and M.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Slovenian Research Agency (L5-1845, L54142, and P5-0147).

**Acknowledgments:** The authors would like to sincerely thank all participants for their involvement, as well as Bojan Nemec, Zlatko Matjaˇciˇc, and Andrej Olenšek for development of the skiing simulator.

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