**2.2 Search strategy**

This review identified the studies fulfilling the above criteria in the systematic review of Larsson et al. (Larsson et al., 2007). Furthermore, we modified their search strategy in the following ways: ((muscle OR pain) AND microdialysis) OR (muscle AND pain AND induced) AND (Humans[Mesh] AND (Clinical Trial[ptyp] OR Meta-Analysis[ptyp] OR Review[ptyp]) AND English[lang] AND adult[MeSH] AND "last 10 years"[PDat]).

Using this strategy, PubMed was searched. From this search, the titles and abstracts were scrutinized. If the articles were relevant and necessary, they were read for further evaluation. We also checked reference lists of these articles. If the article was relevant according to our aim and inclusion criteria, we listed the results in tables. The tables of the different conditions reported the statistics concerning comparisons between the patient group and control group with respect to baseline data or corresponding data for all investigated substances. Moreover, we listed gender, flow rate, number of subjects in each group, and if and how the authors handled RR.

### **2.3 Positive outcome with respect to potential biomarker**

A specific substance was classified as a potential biomarker if the majority of studies (including the majority of subjects) showed significantly lower or significantly higher concentrations in the patient group compared to the controls.
