**4. Materials and Methods**

The authors researched the PubMed/MEDLINE electronic database by using terms consisting of the following: (AKI biomarker or cystatin C or NGAL or KIM-1 or urinary interleukin-18 or urinary interleukin or urinary liver-type fatty acid-binding protein or urinary L-FABP or urinary insulin-like growth factor-binding protein 7 or urinary IGFBP7 or urinary tissue inhibitor of metalloproteinases-2 or urinary TIMP-2 or nephrocheck or urinary osteopontin or urinary calbindin or urinary TTF) (nordic walking or physical activity or exercise or marathon or ultramarathon or swimming or cycling or games or football). The search was repeated regularly, and the database was updated until the last update on 13 July 2020, prior to manuscript submission. An additional search was conducted according to a reference list of read papers and by using investigators' names. As the initial selection was done through titles and abstracts, it is possible that some important papers might have been omitted, although the authors tried to identify all that were important. A total of 27 papers were retrieved from 629 titles and abstracts identified in the PubMed database (Figure 2).

In this review, results of 13 additional studies were also shortly discussed. These papers did not consider single exercise in healthy subjects, but revealed important information, and the authors decided to present their results. There was no possibility to perform any statistical analysis because of the high variability of schedules, experimental conditions and different study groups described in the papers cited. Ethical approval was not necessary, because the study did not involve participants.

**Figure 2.** Flow chart illustrating the procedure for article inclusion and exclusion in a systematic review of changes in AKI biomarkers after exercise.

**Author Contributions:** Conceptualization, W.W. and W.R.; resources W.W., W.R. and J.R.; writing—original draft preparation, W.W.; writing—review and editing, W.R., M.R. and J.R.; visualization W.W.; supervision, M.R. All authors have read and agreed to the published version of the manuscript.

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

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