Effect on Growth Assessment: Body composition and muscle tone

Body composition and muscle tone may influence the way weight-for-age and weight-for-stature (or body mass index-for-age) are interpreted. The data used to assess weight and stature proportionality (weight-for-length and body mass index-for-age) are based on children with typical body composition.

Low muscle tone is common among children with some disorders, and this must be taken into consideration. Disorders that are frequently associated with low muscle tone include cerebral palsy, Down syndrome, Prader-Willi syndrome, Fragile X syndrome, and muscular dystrophy. Children with paralysis (e.g., myelomeningocele) will also have altered body composition. Because fat weighs less than muscle, a child with decreased muscle mass and an “acceptable” weight-for-length, may be overfat.