AIM: The aim of this paper was to determine changes of the bioelectrical impedance vector (BIVA) throughout a soccer season and to ascertain whether vector changes are associated with endurance performance changes. METHODS: Eighteen professional male soccer players (age=21.8±3.0 years, 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 preseason training, after the pre-season training and at the end of the season. RESULTS: Vector length shortened (p<0.05) during pre-season training and was associated with improvements in endurance performance (r=0.569, p=0.034). Vector length and phase-angle increased at mid-season compared to post pre-season training (p<0.05). Vector length at end-season was lower compared to mid-season (p<0.05). No further changes in endurance performance occurred. CONCLUSION: Bioimpedance vector variations from baseline indicate that fluid-gains occur during the pre-season training, possibly due to plasma volume expansion and enhanced glycogen storage, accompanied by improvements in endurance performance. The vector migration and the increase in phase angle during the competitive season indicate fluid-loss and an increase in body cell mass without effects on performance. At the very end of the season, when training volume and intensity are reduced, body fluid increases again.
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