The Usefulness Of Bioelectrical Impedance To Monitor The Performance In Professional Soccer Players During A Sport Season

PURPOSE Bioelectrical impedance vector analysis (BIVA) is a method that identifi es changes of hydration status and soft tissue mass by solely considering impedance components. This method eliminates the major weaknesses described for BIA, i.e. dependency on equations and euhydration status. The Yo-Yo Intermittent Recovery Test is an incremental and sensitive method to asses any possible soccer performance changes. This study determines changes of the vector position throughout a soccer season and investigates whether vector changes are associated with performance changes. METHODS On 8 occasions during a soccer season, bioelectrical impedance measurements were performed on an Italian professional football team (4th division, n=18, age: 21.8±3.0 yr, height: 180.0±7 cm, weight: 74.2±6.5 kg), and cardio-respiratory endurance was assessed before and after the pre-season training. RESULTS Signifi cant difference of the vector length were found between before pre-season training (T1: Rz=496.4±37.9, Xc=65.8) and the beginning of the competition period (T2: Rz=481.1±36.6, Xc=62.5±5.0; T3: Rz=485.5±32.6, Xc=62.9) (p<.05). Decreases in vector length (Δ vector length) were associated with improvements in endurance (Δ Yo-Yo test from 19828.5±407.9 m to 2308.6±509.2 m) performance (r=.569, p=.034). After the pre-season training (T2-3) vector positions varied when compared to values recorded throughout the season (mean value of period T4-7: Rz=498.8±3.7, Xc=70.1±0.9). Vector length at the end of the season (T8: Rz=479.9±38.5, Xc=68.0±7.9) was different when compared to T4-7. CONCLUSION Vector changes throughout the season indicate that fl uid gains occur during the preseason training. They are possible due to plasma volume expansion and the related impedance changes accompany improvements in endurance performance. During the competitive season, fl uid loss occurs but with a concomitant increase in soft tissue mass. This could indicate that players gain muscle mass throughout the season but are not able to maintain hydration status. Yet, at the very end of the season, when training volume and intensity might be reduced, body fl uid increases again.