ARTICLE Biochemical impact of soccer: an analysis of hormonal, muscle damage, and redox markers during the season João Renato Silva, António Rebelo, Franklim Marques, Laura Pereira, André Seabra, António Ascensão, and José Magalhães Abstract: This study aimed to analyze changes in performance, muscle function, and stress-related biochemical markers in profes- sional soccer players (n = 14) at 4 timepoints (3 for performance and 4 for stress-related biochemical markers) during the soccer season O preseason (E1), midseason (E2), end of the season (E3) O and after the end of the recovery period (E4). Performance in 5- and 30-m sprints, countermovement jump, and agility, and maximal isokinetic knee extension and knee flexion strength were measured (E1 to E3). We observed increased in-season levels of myoglobin (E2 > E1 and E4; p < 0.05), a higher testosterone/cortisol ratio (T/C), and increased levels of creatine kinase (CK), C-reactive protein, superoxide dismutase (SOD), protein sulfhydryls (–SH), and malondialde- hyde (E2 and E3 > E1 and E4; p < 0.05). Lower cortisol concentrations (E3 < E1 and E4; p < 0.05) and glutathione reductase activity (E3 < E2 and E4; p < 0.05) were observed at the end of the season. T/C, CK, SOD, –SH, and malondialdehyde decreased during the off-season, and cortisol and glutathione reductase increased (E3 < E4; p < 0.05). Agility increased in E2 and E3 (p < 0.01). Significant correlations were found during the season between hormonal and muscle function parameters (r = 0.56–0.86; p < 0.05). In addition, in E2, significant associations were observed between match-accumulated time (MAT E2 ; minutes played by each player during the competition period), performance, and hormonal and redox parameters (r = 0.456–0.615; p < 0.05). In conclusion, this study shows that soccer players face significant changes in biomarkers of physiologic strain (muscle damage and oxidative stress-related markers) during the season, but values return to normal during the off-season. Additionally, MAT influences physical, hormonal, and oxidative stress-related parameters in professional soccer players. Key words: performance monitoring, biochemical monitoring, testosterone, cortisol, muscle damage, inflammation, antioxidant system, oxidative stress, match exposure. Résumé : Cette étude analyse les variations de la performance, de la fonction musculaire et des marqueurs biochimiques associés au stress (3 variables pour la performance et 4 pour les marqueurs biochimiques associés au stress) chez des joueurs de soccer professi- onnel (n = 14) tout au long de la saison (avant-saison (E1), milieu de la saison (E2), fin de la saison (E3) et après la fin de la période de récupération (E4)). On évalue (E1–E3) aussi la performance au sprint de 5 et 30 m, au saut avec contremouvement préparatoire et a ` un test d’agilité ainsi que la force isocinétique maximale a ` l’extension du genou et a ` la flexion du genou. Durant la saison, on observe une augmentation des valeurs de myoglobine (E2 > E1 et E4; p < 0,05), du ratio testostérone/cortisol (T/C), de la créatine kinase (CK), de la protéine C-réactive, de la superoxyde dismutase (SOD), des groupes sulfhydryles des protéines (–SH) et du malonaldéhyde (E2 et E3 > E1 et E4; p < 0,05). À la fin de la saison, on observe une plus faible concentration de cortisol (E3 < E1 et E4; p < 0,05) et une diminution de l’activité de la glutathion réductase (GR) (E3 < E2 et E4; p < 0,05). Hors saison, on observe une diminution de T/C, CK, SOD, –SH et de malonaldéhyde et une augmentation de C et de GR (E3 < E4; p < 0,05). L’agilité augmente a ` E2 et a ` E3 (p < 0,01). En saison, on enregistre des corrélations significatives entre les variables hormonales et musculaires (r = 0,56–0,86; p < 0,05). De plus, dans E2, on observe des corrélations significatives entre le nombre de minutes de compétition accumulées au milieu de la saison par un joueur (« MAT E2 ») et la performance, les variables hormonales et de redox (r = 0,456–0,615; p < 0,05). En conclusion, cette étude révèle des modifications significatives des biomarqueurs du stress physiologique (lésions musculaires, stress oxydatif) durant la saison, mais les valeurs reviennent a ` la normale hors saison. En outre, le MAT a un effet sur les variables physiques, hormonales et le stress oxydatif chez les joueurs de soccer professionnel. [Traduit par la Rédaction] Mots-clés : suivi de la performance, suivi biochimique, testostérone, cortisol, lésion musculaire, inflammation, système antioxydant, stress oxydatif, exposition a ` la compétition. Introduction Accumulated levels of physiologic stress during the playing sea- son might predispose soccer players to an inability to cope with training and competitive demands, thus compromising perfor- mance. In fact, the metabolic and mechanical stress imposed on soccer players might induce physiologic disturbances that could be exacerbated during periods of prolonged or intense exposure. There are reports of alterations in the anabolic and catabolic hor- monal environments (Kraemer et al. 2004; Handziski et al. 2006), muscle damage markers (Heisterberg et al. 2013; Meister et al. 2011), and immunologic (Rebelo et al. 1998) and redox states after periods of high-intensity soccer training and competition Received 28 April 2013. Accepted 27 October 2013. J.R. Silva. Center of Research, Education, Innovation and Intervention in Sport (CIFI2D), Rua Dr. Plácido Costa, 91, 4200-450 Porto, Portugal; National Sports Medicine Programme Excellence in Football Project, Aspetar-Qatar Orthopaedic and Sports Medicine Hospital, Doha, Qatar. A. Rebelo. Center of Research, Education, Innovation and Intervention in Sport (CIFI2D), Rua Dr. Plácido Costa, 91, 4200-450 Porto, Portugal. F. Marques and L. Pereira. Institute for Molecular and Cell Biology (IBMC), University of Porto, Porto, Portugal. A. Seabra, A. Ascensão, and J. Magalhães. Research Center in Physical Activity, Health and Leisure (CIAFEL), Portugal; Rua Dr. Plácido Costa, 91, 4200-450 Porto, Portugal. Corresponding author: João Renato Silva (e-mails: jm_silv@hotmail.com, joao.silva@aspetar.com). 432 Appl. Physiol. Nutr. Metab. 39: 432–438 (2014) dx.doi.org/10.1139/apnm-2013-0180 Published at www.nrcresearchpress.com/apnm on 28 October 2013.