, 1985; Reilly and Thomas, 1977). As a result of such a training program, strength gains among soccer players can be observed. For example, it was reported that regular players when compared to substitutes, thorough and professional players when compared to amateurs, have superior isokinetic muscle strength at various angular velocities (Cometti et al., 2001; Wisloff et al., 1998). There are various studies in which researchers examined the pre-season physiological and physical changes of soccer players over a period of 6�C8 weeks. Most of this research focused on endurance, power, and anthropometric measurements (Bangsbo, 1994; Brady et al., 1997; Brewer, 1990; Casaj?s, 2001; De Proft et al., 1988) and limited research reported isokinetic strength changes at slower velocities in soccer players (Reilly and Thomas, 1977).
However, no research examined the isokinetic strength changes at higher angular velocities in elite soccer players over a competitive season. Various environmental stimuli during soccer training and competition might result in certain long-term physiological adaptations to improve players�� endurance and speed, as well as strength. The biggest argument for including high-velocity exercise in a player��s resistance-training program deals with the concept of specificity (Murray, 2006). Soccer players apply high-speed movement for sprint performance during a match. Training with high-speed movement in strength exercises enables high-speed adaptation. Consequently, soccer players should practice their exercises at high speed.
Also, high-velocity exercises may have an appropriate place in a periodized resistance-training program designed for players who require speed (Kawamori and Newton, 2006). Therefore, the aim of this study was to evaluate the seasonal changes in isokinetic strength of knee muscles at various angular velocities in Turkish elite soccer players over the course of a 24-week soccer season that included regular daily practice and one or two regular matches per week. The authors attempted to answer the question how elite soccer players adapted to the effects of conditioning, practice, and high level competition over an entire season by assessing their strengths at two different time points. Material and methods Subjects Fourteen soccer players, 18�C32 years of age, all members of a professional soccer team in the Turkish Soccer Super League, participated in the study.
Before conducting the experiment, all subjects were informed on the risks of the study and gave informed consent, and it was a part of their professional contract. The study was approved by the Ethics Committee of the Celal Bayar University and met the conditions of the Helsinki Declaration. All soccer players participated in the 24-week soccer-specific Brefeldin_A training and competitions as regular and/or substitute players. Players with a long history of injuries were eliminated from the study.