The Association of Grip Strength, Body Mass Index, and Lung Function in Youth with Cystic Fibrosis

Abstract

Compared with body mass index (BMI), lean body mass and fat‐free mass are strongly associated with lung function in children and adolescents with cystic fibrosis (CF). Methods of measuring body composition in youth with CF are often unreliable, expensive, or not clinically feasible. Grip strength (GS), a measure of muscle function, is used as a surrogate for muscle mass and is an indicator of nutrition status. This quality improvement project explored the feasibility of measuring GS in medically stable youth with CF, aged 6–21 years. A total 361 GS measurements were performed by using a digital hand dynamometer in youth from a single CF center. Using reference tables that were created for this project by merging data from the 2011–2012 and 2013–2014 National Health and Nutrition Examination Surveys, youth with CF were found to be weaker than age‐ and gender‐matched peers, even when controlled for differences in size. A positive association (P < .001) was found between GS percentile and lung function, as measured by forced expiratory volume in 1 second percent predicted (FEV1pp). Statistical analysis revealed that both BMI percentile and absolute GS (AGS) percentile were positively associated with FEV1pp and with each other, primarily at the lower levels of BMI percentile (<50%) and AGS percentile (<50%). GS may provide a reliable, less expensive, and clinically feasible alternative to body composition measurements in monitoring nutrition status in youth with CF, especially in youth whose BMI is in the <50th percentile.