Cross-sectional Study of Self-reported Physical Activity and BMI in Adolescents: The Role of Gender and Age

This cross-sectional study examined the association between physical activity and body mass index (BMI) among 754 middle school students (39.5% female, 60.5% male; aged 15-18 years).Both BMI and physical activity were derived from self-reported data: weight and height were used to calculate BMI, while the frequency, duration and intensity of physical activity were assessed using the International Physical Activity Questionnaire (IPAQ).Logistic regression was applied to analyze the influence of activity, gender and grade on overweight status.Overall, 73.2% of students reported meeting the WHO guideline of 60 minutes of moderate-to-vigorous activity per day, while 26.8% did not.Clear gender-and grade-specific differences emerged: girls, particularly in the third and fourth grades, were disproportionately represented among those reporting less than 60 minutes of daily activity, whereas boys more frequently met the recommendations.The regression model was statistically significant ((5) = 29.76,p < .001),explaining 3.9% (Cox & Snell R) to 5.7% (Nagelkerke R) of the variance.Gender and grade were significant predictors, while activity level was not (B = -0.10,p = .63,OR = 0.91, 95% CI [0.64, 1.29]).Boys had 38% lower probability of being overweight than girls (B = -0.48,p = .009,OR = 0.62, 95% CI [0.43, 0.89]).Compared with grade 4, overweight risk was significantly lower in grade 1 (OR = 0.33, p < .001),grade 2 (OR = 0.44, p = .001),and grade 3 (OR = 0.47, p = .001).These findings highlight gender-and age-related differences in activity and overweight.Preventive strategies should be specifically adapted for girls in higher grades.