404 ORIGINAL RESEARCH Pediatric Exercise Science, 2015, 27, 404 -411 http://dx.doi.org/10.1123/pes.2014-0175 © 2015 Human Kinetics, Inc. Burns, Brusseau, and Eisenman are with the Dept. of Exer- cise and Sport Science, University of Utah, Salt Lake City, UT. Hannon is with the Dept. of Physical Activity and Sport Sciences, West Virginia University, Morgantown, WV. Saint- Maurice and Welk are with the Dept. Of Kinesiology, Iowa State University, Ames, IA. Mahar is with the Dept. of Kinesioloogy, East Carolina University, Greenville, NC. Address author cor- respondence to Ryan D. Burns at ryan.d.burns@utah.edu. Cross-Validation of Aerobic Capacity Prediction Models in Adolescents Ryan D. Burns University of Utah James C. Hannon West Virginia University Timothy A. Brusseau and Patricia A. Eisenman University of Utah Pedro F. Saint-Maurice and Greg J. Welk Iowa State University Matthew T. Mahar East Carolina University Cardiorespiratory endurance is a component of health-related itness. FITNESSGRAM recommends the Progres- sive Aerobic Cardiovascular Endurance Run (PACER) or One mile Run/Walk (1MRW) to assess cardiorespira- tory endurance by estimating VO 2 Peak . No research has cross-validated prediction models from both PACER and 1MRW, including the New PACER Model and PACER-Mile Equivalent (PACER-MEQ) using current standards. The purpose of this study was to cross-validate prediction models from PACER and 1MRW against measured VO 2 Peak in adolescents. Cardiorespiratory endurance data were collected on 90 adolescents aged 13–16 years (Mean = 14.7 ± 1.3 years; 32 girls, 52 boys) who completed the PACER and 1MRW in addition to a laboratory maximal treadmill test to measure VO 2 Peak . Multiple correlations among various models with measured VO 2 Peak were considered moderately strong (R = .74–0.78), and prediction error (RMSE) ranged from 5.95 ml·kg -1, min -1 to 8.27 ml·kg -1. min -1 . Criterion-referenced agreement into FITNESSGRAM’s Healthy Fitness Zones was considered fair-to-good among models (Kappa = 0.31–0.62; Agreement = 75.5–89.9%; F = 0.08–0.65). In conclusion, predic- tion models demonstrated moderately strong linear relationships with measured VO 2 Peak , fair prediction error, and fair-to-good criterion referenced agreement with measured VO 2 Peak into FITNESSGRAM’s Healthy Fitness Zones. Cardiorespiratory endurance is an important domain of health-related itness because of its links to cardio-met- abolic health in both the pediatric and adult populations (3,12). Results from the National Health and Nutrition Examination Survey (NHANES) shown that more than one-third of American children and adolescents have inadequate levels of cardiorespiratory endurance (6,26). Cardiorespiratory endurance also tracks reasonably well from childhood through adolescence (24), therefore chil- dren who have low cardiorespiratory endurance levels also tend to have low levels throughout their adolescent years and into adulthood. FITNESSGRAM, designated as America’s youth itness test by the President’s Council on Fitness, Sports and Nutrition (https://www.presidentschallenge.org/chal- lenge/pyfp.shtml), recommends the use of the Progressive Aerobic Cardiovascular Endurance Run (PACER) or the One-mile run/walk (1MRW) to assess aerobic capacity (i.e., VO 2 Peak ). Although the 1MRW is still widely used as a cardiorespiratory endurance ield test, it is the PACER, developed by Leger and Lambert (18), which is FIT- NESSGRAM’s primary (default) test. The PACER has displayed correlation coeficients ranging from r = .60 to .87 with measured VO 2 Peak (19,23), and has demonstrated