Introduction: Isokinetic extension and flexion peak torques are frequently used to assess strength possibilities of volleyball players in different periods of an annual macrocycle (Hadzic et al., 2010; Rousanoglu et al., 2013). Much less attention has, however, been paid to quantify irregularities on isokinetic torques time-curves occurring during the competitive season. The aim of this work is thus to inspect such undulations using a discrete wavelet transform methodology. It was hypothesised that a time-frequency analysis was suitable to quantify the changes in the knee extension torque characteristics throughout the annual macrocycle. Methods: The research was conducted among 13 volleyball players from a second-division team. The torque of knee extensors was measured using Biodex System Pro4. The measurements were done at the end of four different periods of the annual macrocycle: the transition period, the preparatory period, as well as the first and the second rounds of the competition. A Daubechies 4 wavelet was chosen for a time-frequency analysis of the signal originating from the dynamometer. ANOVA with repeated measures was applied to check the differences among the research variables. Results: The wavelet decomposition revealed significant differences in high frequency energy content between the first and fourth (p<=0,0087), the second and fourth (p<=0,0097) and between the third and the fourth (p<=0,021) measurements. There were no statistically significant differences between the first three measurements. Discussion: The high frequency energy contained within the details of the decomposed signal detected after the second round of the competition may reflect indirectly a fatigue of the knee extensors. The changes in energy spectrum have been already observed in biomechanics Tsepis et al. (2004) who reported the higherfrequency content in the isokinetic time-torque characteristics of ACL deficient knees compared to the intact ones. The obtained results may be of practical value, since they can help to assess the players` muscle fatigue during the macrocycle, verify and modify the training methods which are being used, and adopt an individual approach to each player.
© Copyright 2016 21st Annual Congress of the European College of Sport Science (ECSS), Vienna, 6. -9. July 2016. Veröffentlicht von University of Vienna. Alle Rechte vorbehalten.