AbstractThe aim of the study was to evaluate the impact of the competitive phase on physiological and metabolic indices and selected markers of skeletal muscle damage in male volleyball players. The study group consisted of 24 young male volleyball players. During the study, participants underwent two series of measurements, before and after the competitive phase of the annual training cycle. In both study terms, players performed an incremental treadmill running test to determine their ventilatory threshold and maximal oxygen uptake. Venous and capillary blood samples were taken for biochemical analysis. There was no significant difference in the physical fitness level, values of biochemical variables and the level of antioxidant status in the surveyed athletes between the two study terms. Significant changes within skeletal muscle damage markers were observed between the beginning and the end of the competitive period: an increase in the concentration of cellular DNA damage products (8-hydroxy-2′-deoxyguanosine; p < 0.0001) and a decrease in muscle activity of creatine kinase (p<0.05). In spite of the increment in cell damage markers, the unaffected level of physiological and biochemical markers may indicate that the experienced cell destruction did not negatively affect the level of physical fitness. When designing the annual training plan, coaches and athletes need to take into consideration that temporary physiological states – oxidative stress and inflammation – may be required to attain training adaptation.