Tri-Ponderal Mass Index and Fitnessgram BMI Classification In Sixth-grade Children

Abstract

To classify the health status of children, criterion standards for body composition and body mass index (BMI) have been established by FITNESSGRAM according to gender and age. Standards for aerobic capacity (AC) have also been established to assess cardiorespiratory function. Tri-Ponderal Mass Index (TMI) has been shown to better classify overweight and obesity than BMI in youth. PURPOSE: The purpose of this study was to determine the association between TMI and FITNESSGRAM BMI classification in sixth-grade children. METHODS: Subjects were 439 sixth-grade boys and girls, ages 11-13, who completed each of the FITNESSGRAM components as a part of their yearly assessment. In addition to height and weight, subjects’ AC was determined from one-mile run/walk times, age, gender and BMI. 43% percent of these students were classified within the Healthy Fitness Zone (HFZ) for BMI. 42% percent of these students were classified as High Risk for BMI. RESULTS: The correlation between TMI and BMI was .98, and the correlation between BMI and AC was -.82. The correlation between TMI and AC was -.80. Receiver Operating Characteristic (ROC) analysis indicated that a TMI of 13.97 represents the best cut-off score for classifying girls within the HFZ for BMI, with 94% classified correctly, and AUC = .98. Also, a TMI of 13.41 represents the best cut-off score for classifying boys within the HFZ for BMI, with 94% classified correctly, and AUC = .98. For determining High Risk classification for BMI, a TMI of 14.90 represents the best cut-off score for classifying girls as High Risk for BMI, with 96% classified correctly, and AUC = .99. Also, a TMI of 15.24 represents the best cut-off score for classifying boys as High Risk for BMI, with 94% classified correctly, and AUC = .98. CONCLUSIONS: TMI is strongly associated with classification according to FITNESSGRAM BMI standards in sixth-grade children. These data suggest that a TMI of 13.97 for girls and 13.41 for boys are the best criteria for HFZ classification for FITNESSGRAM BMI. Also, a TMI of 14.90 for girls and 15.24 for boys are the best criteria for High Risk classification for FITNESSGRAM BMI. TMI is a substantial factor in determining overweight and obesity, and body size has been shown to be an important health-related outcome, especially in youth.