Applicability of anthropometric indices for assessing speed and agility in children and adolescents: proposed reference values by age and sex

OBJECTIVE: a) To verify the applicability of anthropometric indices (body mass index (BMI), tri- weight index (TWI), body surface area (BSA)) for evaluating velocity and agility tests in children and adolescents, and to propose reference values. METHODS: A descriptive cross-sectional (correlational) study was designed in 1573 schoolchildren aged 6 to 17 years. Weight and height were assessed. BMI, TWI, and BSA were calculated. The 20-meter sprint and agility (5 meters x 10 repititions) test was evaluated. RESULTS: In the individual analysis, the explanatory power for velocity and agility for BMI was almost nil. In the case of the TWI (r² = 0.123 and 0.110) and BSA (r² = 0.157 and 0.211), they showed significant explanatory power. When age was incorporated, the predictive power significantly increased. For BMI+age (r² = 0.342 and 0.435); TWI+age (r² = 0.382 and 0.467), and BSA+age (r² = 0.292 and 0.394). When sex was added, the results showed a further improvement. For BMI+age+sex (r² = 0.409 and 0.498); TWI+age+sex (speed test (r² = 0.435 and 0.517) and BSA+age+ sex (r² = 0.373 and 0.470). CONCLUSION: The TWI better explained motor performance than the BMI and BSA in Chilean schoolchildren. Models that included TWI along with age and sex indicated that the TWI could be an alternative for assessing velocity and agility. Furthermore, percentiles were developed for the 20-meter sprint and the 5-meter agility test (10 repetitions), which are useful for monitoring and interpreting changes in the physical performance of schoolchildren.