Physical Fitness in 9–11 Italian Children Is Influenced by Sex, Chronological Age, BMI, and Frequency of Sport Practice but Not by Maturity or Relative Age

This study aimed at analyzing physical fitness in 9-11 years-old children, in relation to: sex, chronological and biological age (Peak Height Velocity, PHV), relative age effect (RAE), body mass index (BMI), levels of sport practice (SP), and sex and chronological age interacted sub-groups. One-thousand-one-hundred-forty-three Italian primary school children (50.7% males) performed anthropometric measurements (body mass, height, BMI) and physical tests for meas-uring coordination (Plate Tapping, PT), handgrip strength (HandGrip, HG), lower-limb power (standing long-jump, SLJ), low-back flexibility (sit-and-reach, SR) and sprint (20m sprint, 20m) skills. Non-parametric tests were applied for verifying fitness differences between subgroups. Higher male values for HG, SLJ, and 20m (p range=0.019-< 0.001), and higher female outcomes in SR (p< 0.001) emerged. For chronological age, effects resulted for each test (p range=0.011-< 0.001). Considering sex and chronological age interacted subgroups, sporadic differences emerged for PHV and RAE, whereas effects frequently resulted for BMI (especially for HG and SLJ tests) and SP (especially for SLJ and 20m tests). Physical fitness in 9-11 years-old Italian students resulted strongly discriminable by BMI and SP, thus highlighting how an adequate lifestyle and fitness should be regularly promoted. Conversely, biological ages and RAE seem to be factors not char-acterizing non-competitive pre-puberty subjects.