Physical Fitness, Body Composition, Somatotype, and Phantom Strategy (Z-Score) in U13, U15, and U17 Female Soccer Players: A Comparative and Correlational Study

Background: Some studies have suggested that physical fitness and body composition may influence individual and collective performance. However, it is necessary to be able to define the relationships between these variables in soccer players of different ages. Objective: To determine the relation between physical fitness level, body composition, and somatotype in female youth soccer players in response to age. Materials and methods: A total of 56 players were evaluated: 19 early adolescents (EA–U13) with a body mass of 48.35 ± 5.67 kg and a height of 157.63 ± 5.55 cm, 21 middle adolescents (MA–U15) with a body mass of 54.02 ± 5.96 kg and a height of 160.37 ± 5.25 cm and 16 late adolescents (LA–U17) with a body mass of 55.37 ± 6.15 kg and a height of 162.39 ± 5.77 cm. The physical fitness tests were: Squat Jump (SJ), Countermovement Jump (CMJ), Countermovement Jump with Arms (CMJA), Single Leg Countermovement Jump, COD-Timer 5-0-5, COD-Timer 5+5, Speed 15 m, Hamstring Strength, and Running-Based Anaerobic Sprint Test (RAST). The International Society for the Advancement of Kinanthropometry (ISAK) protocols were used to determine anthropometric measurements (skinfolds, circumferences, bone diameters), and the Heath-Carter method was used to assess body composition and somatotype, with z-scores calculated using the Phantom strategy. Results: The analysis revealed that the most significant differences between groups were observed in general anthropometric measurements (ω2 = 0.84), followed by sitting height (ω2 = 0.51) and percentage of body fat according to Carter’s method (ω2 = 0.24), all with large and statistically significant effect sizes (p < 0.05). Larger muscle and bone dimensions, especially in the hip, thigh, and calf, are closely related to better strength, power, and initial sprint speed performance in female soccer players. Conclusions: This study reaffirms that muscle mass is a key predictor of athletic performance, along with strength at high speeds, promoting improvements in power and sprinting in the initial meters. Adiposity is a limiting factor for youth soccer players. Age progression and biological maturation favor the development of the mesomorphic profile, optimizing strength and power.