*Article* **Differences between Professional and Amateur Cyclists in Endogenous Antioxidant System Profile**

**Francisco Javier Martínez-Noguera 1,\*, Pedro E. Alcaraz 1, Raquel Ortolano-Ríos 1, Stéphane P. Dufour 2,3 and Cristian Marín-Pagán <sup>1</sup>**


**Abstract:** Currently, no studies have examined the differences in endogenous antioxidant enzymes in professional and amateur cyclists and how these can influence sports performance. The aim of this study was to identify differences in endogenous antioxidants enzymes and hemogram between competitive levels of cycling and to see if differences found in these parameters could explain differences in performance. A comparative trial was carried out with 11 professional (PRO) and 15 amateur (AMA) cyclists. All cyclists performed an endogenous antioxidants analysis in the fasted state (visit 1) and an incremental test until exhaustion (visit 2). Higher values in catalase (CAT), oxidized glutathione (GSSG) and GSSG/GSH ratio and lower values in superoxide dismutase (SOD) were found in PRO compared to AMA (*p* < 0.05). Furthermore, an inverse correlation was found between power produced at ventilation thresholds 1 and 2 and GSSG/GSH (r = −0.657 and r = −0.635; *p* < 0.05, respectively) in PRO. Therefore, there is no well-defined endogenous antioxidant enzyme profile between the two competitive levels of cyclists. However, there was a relationship between GSSG/GSH ratio levels and moderate and submaximal exercise performance in the PRO cohort.

**Keywords:** catalase; superoxide dismutase; oxidized glutathione; reduced glutathione; hemoglobin; power output
