Longitudinal analysis of body composition in Italian national U17 male handball players using bioelectrical impedance vector analysis.

The bioelectrical impedance vector significantly lengthened from end of season to pre-season, then shortened progressively through season onset and winter break.

• Vector significantly lengthened from T0 (end of season) to T1 (pre-season) with Mahalanobis distance D=1.95
• Vector shortened from T1 to T2 (season onset) with D=1.63
• Vector continued to shorten from T2 to T3 (winter break) with D=0.88
• Statistical significance was set at P<0.05 using repeated measures mixed models
• Sample consisted of 15 male U17 Italian national handball players (age: 16.44±0.60 years)

Stature-adjusted resistance decreased significantly across the season, reaching its lowest value at winter break.

• Stature-adjusted resistance at T1 (pre-season) was 275.6 Ω/m±27.8
• Resistance significantly decreased at T2 (season onset) to 262.9 Ω/m±26.1 compared to T1
• Resistance reached its lowest at T3 (winter break) at 249.7 Ω/m±21.4, significantly lower than T0 (269.7 Ω/m±27.9), T1, and T2
• Decreasing resistance is indicative of increased hydration status during the competitive season

Stature-adjusted reactance significantly increased during pre-season then decreased through the competitive season.

• Stature-adjusted reactance at T0 (end of season) was 35.3 Ω/m±3.6
• Reactance significantly increased at T1 (pre-season) to 39.00 Ω/m±3.7 compared to T0
• Reactance decreased at T2 (season onset) to 36.2 Ω/m±3.2 compared to T1
• Reactance further decreased at T3 (winter break) to 35.7 Ω/m±3.4 compared to T1

Phase angle, total body water percentage, and fat-free mass percentage all increased significantly from end of season to winter break.

• Phase angle increased from 7.4°±0.5 at T0 to 8.1°±0.6 at T3
• Total body water increased from 59.9±3.6% at T0 to 61.1±3.7% at T3
• Fat-free mass increased from 82.0±4.5% at T0 to 84.0±5.1% at T3
• All three variables showed statistically significant increases over the full observation period (T0 to T3)

Four distinct time points across a full annual cycle were monitored to capture different phases of training and competition.

• T0 corresponded to end of the previous season
• T1 corresponded to pre-season preparation
• T2 corresponded to season onset
• T3 corresponded to winter break
• Repeated measures mixed models were used for statistical analysis, with Mahalanobis' tests used to track vector shifts and ellipse distances