Normalizing and Standardizing Physical Fitness by Sex, Age, and Body Size in Brazilian Children and Adolescents: A PROESP-BR Study

The study aimed to use allometric modeling to identify how body size dimensions should be exponentiated to normalize physical fitness variables. It also aimed to provide reference values to standardize physical fitness into z-scores by sex, age, and body size dimensions. Cross-sectional data from 95,691 Brazilian children and adolescents (52,747 males; 55.1%; aged 6-18 years) were analyzed, including physical fitness tests (abdominal endurance, agility, cardiorespiratory fitness, flexibility, lower and upper limbs power, and speed) and anthropometric measures (arm span, body mass, and height). Allometric modeling was applied, and statistical significance was determined using p values less than 0.05. Results revealed that taller individuals with longer levers generally performed better in physical fitness tests (p ≤ 0.007), regardless of biologic sex and chronologic age, except for flexibility tests where shorter individuals with longer upper limbs performed better (p ≤ 0.001). The impact of greater body mass varied depending on whether the test required the individual to carry his/her own weight. Among females, performance in weight-bearing/carrying tests peaked at middle adolescence and declined thereafter, while among males, performance steadily increased with age. In conclusion, the present study provided reference equations to calculate z-scores independent from biologic sex and chronologic age and dimensionless to body size variables, and also suggested how arm span, body mass, and height could be exponentiated for use in the denominator of a physical fitness scaled ratio or index.