Eighteen professional male soccer players (age = 21.8±3.0 yr, height = 1.8±0.07 m, mass =7.2±6.5 kg) participated in the study. BIVA was conducted serially on 8 occasions throughout one soccer season. Endurance performance (Yo--Yo test) was assessed before the first training session of the pre--season training, after the pre--season training and at the end of the season.