Muscular Fitness Levels of U.S. Children and Adolescents

Purpose: To describe muscular fitness (MF) levels and percentile benchmarks among U.S. children and adolescents aged 6–15 years old across sociodemographic, physiological, and behavioral subgroups. Methods: Data were from the 2012 NHANES National Youth Fitness Survey (NNYFS). Four strength tests consisting of the plank, knee extension, modified pull-up, and handgrip, were analyzed by age, sex, race/ethnicity, income, BMI category, cardiorespiratory fitness (CRF), and physical activity (PA) among 1,234 participants (51% male) using SAS SURVEY procedures. Results: Mean ± SEM scores were 69.6 ± 1.8 s (plank), 56.6 ± 4.2 lb (left) and 59.2 ± 4.3 lb (right) knee extension, 5.5 ± 0.3 pull-ups, and 21.2 ± 0.3 kg handgrip strength. Male adolescents (12–15 y) scored higher than females on all tests (p < .05). Non-Hispanic Black youth outperformed White and Mexican American peers on knee extension (p < .05), whereas Mexican American youth had the lowest scores. Healthy-weight youth performed better on plank and pull-ups, while peers with obesity showed higher knee extension and grip strength (p < .005). Adolescents in the Healthy Fitness Zone for CRF outperformed high-risk peers on plank, pull-up, and grip tests (p < .001). Children meeting PA guidelines completed more pull-ups (p < .005) but had lower knee extension and grip strength (p < .01). Percentile analyses revealed similar patterns but greater variability and widening disparities toward the upper percentiles. Plank ranged from 36 s (25th) to > 127 s (90th), knee extension from ~33 lb to > 100 lb, handgrip from 14 to > 33 kg, and pull-ups from 0 to 13 reps. Conclusions: These nationally representative MF benchmarks for U.S. youth highlight subgroup disparities and support the need for continued surveillance to guide youth strength promotion initiatives.