MELATONIN AND OTHER PARAMETERS OF BLOOD ANTIOXIDANT SYSTEM IN VOLLEYBALL PLAYERS DURING AN ANNUAL TRAINING CYCLE.

Purpose. The aim of the study was to analyze changes in prooxidant-antioxidant balance parameters, with special focus on melatonin as an antioxidant, in volleyball players during an annual training cycle. Basic procedures. The study was attended by eleven volleyball players aged 16-17 years from the UKS "Budowlanka" Poznań sports club. The measurements were taken on five dates: in the preparatory "A" period (September 2002), in the pre-starting period (October 2002), in the starting period (March 2003), in the transient period (May 2003) and in the preparatory "B" period (September 2003). On all the dates, venous blood from the basilic vein was drawn from resting players. The concentration of melatonin (MLT), creatinine and creatine kinase (CK) in venous blood serum was estimated. Also, the total antioxidant capacity (TAS) and concentration of thiobarbituric acid reactive substances (TBARS) in the blood plasma were determined. Main findings. The obtained results showed that the parameters of prooxidant-antioxidant balance in players during an annual training cycle differed significantly in individual periods. The lowest level of concentration of both MLT and TAS occurred in the starting period (the third date of measurements), when the subjects were training with the heaviest physical loads. MLT concentration at the beginning of the pre-starting period, as compared with the preparatory period, was increasing, however, without statistical significance. A highly statistically significant difference was noted between the pre-starting period and the starting period (p ≤ 0.01), when the level of MLT was reduced from 26.04 to 15.2 pg/ml. A statistically significant increase in MLT concentration in relation to the starting period was observed in the transient period (p < 0.05). In the analysis of the concentration of the total antioxidant capacity of plasma (TAS) on five dates of measurements, a significant decrease on the third date, as compared with the first one, was found; from the third date of measurement, the TAS level grew systematically. Nevertheless, the difference in TAS at the beginning and at the end of the study was not statistically significant, although there was a growth tendency from 1.6 to 1.7 mmol/l. In the period between the first and the third dates of measurement, an increase was observed in the concentration of TBARS, i.e. products of peroxidation of lipids reacting with thiobarbituric acid. On the third date of measurement, the concentration of the compound in question increased significantly (p ≤ 0.01), as compared with the second date of measurement; on the fourth date, no statistically significant changes in the concentration of this parameter were observed. Conclusions. (1) The average resting concentration of melatonin in blood serum depends on the type of training load, which confirms its participation in eliminating oxidative stress induced by the character of training load. (2) Concentrations of the studied oxidative stress parameters in the blood of volleyball players in individual mesocycles of an annual training cycle seem to be determined by the type of training load. The lowest concentrations of the parameters of the antioxidant system were observed in the starting period, i.e. when the players were training with the heaviest training loads. [ABSTRACT FROM AUTHOR]