McDonough et al. 2026 / NNYFS muscular fitness
About this reference
McDonough et al. analyzed plank, modified pull-up, knee-extension, and handgrip data from the 2012 National Youth Fitness Survey using SAS survey procedures. Table 2 publishes weighted P10, P25, P50, P75, and P90 values separately for the overall sample, males, females, ages 6-11, and ages 12-15. FitnessNorms downloaded the public Y_PLX and Y_DEMO files, retained recorded plank times for participants aged 6 or older at the examination, applied the NNYFS MEC examination weight, and calculated P5, P25, P50, P75, and P95 in each crossed sex-by-age cell. The weighted empirical CDF uses the interpolation definition documented for SAS PROC SURVEYMEANS. Eligibility keys on RIDEXAGY, the age at examination, rather than RIDAGEYR, the age at screening. That is the specification which reproduces the published analysis exactly: the same 1,209 plank records, the same 69.6-second weighted mean, and all 25 published marginal cut-points to the printed decimal. Screening age instead returns 1,201 records and leaves residuals of up to 0.6 seconds against the paper.
Known limitations
- The measurements were collected in 2012. They are a historical US youth reference and may not describe current fitness levels.
- The published paper reports age and sex marginal percentiles separately. FitnessNorms crossed the paper's native 6-11 and 12-15 age bands with sex in the public microdata; those four crossed tables are an internal derivation, not tables printed in the paper.
- The page reports weighted percentile point estimates without survey-design standard errors or confidence intervals.
- The two broad age bands reduce tail instability but combine children at different stages of growth and biological maturation.
- Plank results depend on posture, correction rules, practice, encouragement, and any time cap. Other plank protocols are not directly interchangeable.
- Eligibility uses the examination age, so six participants who turned 16 between screening and their examination are included in the 12-15 band, matching the published analysis.