title: US youth cardiorespiratory fitness levels: challenges and solutions.
authors.forename: Melita M
authors.initials: MM
authors.lastname: Nasca
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002319:Cardiovascular System; D002648:Child; D006801:Humans; D009043:Motor Activity / Q000502:physiology; D010806:Physical Education and Training; D010809:Physical Fitness / Q000502:physiology*; D012016:Reference Values; D012137:Respiratory System; D014481:United States