Relationship between Body Mass Index and lower limb strength in children and adolescents

Abstract

Background Body mass index (BMI) is an anthropometric indicator used as a predictor of risk in cardiovascular disease and mortality. Objective to verify the linear and nonlinear (quadratic) relationships between BMI and lower limb strength in children and adolescents of both sexes in a region of Chile. Methodology: A descriptive (cross-sectional) study was carried out in children and adolescents of school age (6 to 17 years) of both sexes. The sample size was 863 schoolchildren (500 males and 363 females). Weight, height and the Horizontal jump test (HJ) were evaluated. Body Mass Index (BMI) and Z-BMI were calculated according to age and sex. Results In males, the explanatory power in the linear model (R = 0.15, R2 = 0.02, RMSE = 39.6) is lower than the non-linear quadratic model (R = 0.22, R2 = 0.05, RMSE = 39.0). In females, the explanatory power in the linear model (R = 0.12, R2 = 0.02, RMSE = 23.2) is lower than the quadratic nonlinear model (R = 0.19, R2 = 0.04, RMSE = 22.9). In the Z-IMC scale, men presented HJ values of: [Low BMI 145.4 ± 39.5cm, normal 164.2 ± 33.6cm, and high BMI 109.0 ± 23.2cm]. In females it was: [Low BMI 108.0 ± 23.0cm, normal 113.5 ± 36.3cm, and elevated BMI 91.5 ± 30.4cm]. Conclusion The study verified a curvilinear relationship in the form of a parabola (quadratic) between BMI and the HJ test in children and adolescents of both sexes. Schoolchildren in the extreme BMI categories (low and high BMI) reflected low performance in the HJ in relation to schoolchildren with normal BMI.