Growth Charts for Muscular Strength Capacity With Quantile Regression

IntroductionMuscle strength preservation may play an important role in protecting against cardiometabolic diseases, functional decline, musculoskeletal deterioration, and early all-cause mortality. However, sex-specific strength growth charts and curves using data from a U.S.-representative sample and clinically feasible measurement remain to be established.MethodsA sample of 7,119 individuals, aged 6-80 years, was included from the 2011-2012 National Health and Nutrition Examination Survey. Analyses were performed in 2015. Grip strength was assessed using a hydraulic handheld dynamometer; peak force values were normalized per body mass. Parametric quantile regression was used to determine unique normalized and absolute strength percentiles for men and women. Responses were fitted with a parametric model, involving six powers of age.ResultsGrowth charts and curves were created using output from the quantile regression from reference values of normalized and absolute grip strength corresponding to the fifth, tenth, 25th, 50th, 75th, 90th, and 95th percentiles across all ages. For men, there was a small drop in normalized strength at age 6 years followed by quick growth until about age 25 years. Among women, normalized strength grew gradually until about age 15 years. For both men and women, normalized strength declined throughout middle age and later adulthood; however, these rates were greater among men. More-pronounced patterns of growth and decline were observed for absolute strength in men and women.ConclusionsThe established strength quantiles can easily be incorporated into a clinical setting for screening individuals that would benefit from lifestyle interventions to improve muscular fitness and reduce health risks.