Anthropometric prediction of skeletal muscle cross-sectional area in persons with spinal cord injury

<jats:p> Finding an accurate and affordable method to quantify muscle size following spinal cord injury (SCI) could provide benefits clinically and in research settings. The purpose of this study was to validate the use of anthropometric measurements vs. magnetic resonance imaging (MRI) to evaluate muscle cross-sectional area (CSA) and develop a field equation to predict muscle CSA specific to the SCI population. Twenty-two men with chronic (>1 yr) motor complete SCI participated in the current study. Anthropometric measurements, including midthigh circumference and anterior skinfold thickness (SF<jats:sub>T</jats:sub>), were taken on the right thigh. The anthropometric muscle cross-sectional area (muscle CSA<jats:sub>anthro</jats:sub>) was predicted using the following equation: muscle CSA<jats:sub>anthro</jats:sub> = π[ r − (SF<jats:sub>T</jats:sub>/2)]<jats:sup>2</jats:sup>, where r = thigh circumference/2π. MRI analysis yielded whole thigh CSA (thigh CSA<jats:sub>MRI</jats:sub>), midthigh muscle CSA (muscle CSA<jats:sub>MRI</jats:sub>), midthigh absolute muscle CSA after subtracting intramuscular fat and bone (muscle CSA-IMF<jats:sub>MRI</jats:sub>), subcutaneous adipose tissue (SAT<jats:sub>T</jats:sub>) measured at one site as well as at four sites, and bone CSA. Anthropometric measurements were correlated to the thigh CSA<jats:sub>MRI</jats:sub> [ r<jats:sup>2</jats:sup> = 0.90, standard error of the estimate (SEE) = 17.6 cm<jats:sup>2</jats:sup>, P < 0.001]. Muscle CSA<jats:sub>anthro</jats:sub> was correlated to muscle CSA<jats:sub>MRI</jats:sub> ( r<jats:sup>2</jats:sup> = 0.78, SEE = 16.6 cm<jats:sup>2</jats:sup>, P < 0.001) and muscle CSA-IMF<jats:sub>MRI</jats:sub> ( r<jats:sup>2</jats:sup> = 0.75, SEE = 17.6 cm<jats:sup>2</jats:sup>, P < 0.001). A single SF<jats:sub>T</jats:sub> was correlated to the polar four-site SAT<jats:sub>T</jats:sub> ( r<jats:sup>2</jats:sup> = 0.78, SEE = 0.37 cm, P < 0.001). The average femur CSA and average IMF CSA derived from MRI led to the following field equation: muscle CSA<jats:sub>predicted</jats:sub> = π[(Thigh<jats:sub>circum</jats:sub>/2π) − (SF<jats:sub>T</jats:sub>/2)]<jats:sup>2</jats:sup> − 23.2. Anthropometric measurements of muscle CSA exhibited a good agreement with the gold standard MRI method and led to the development of a field equation for clinical use after accounting for bone and IMF. </jats:p><jats:p> NEW & NOTEWORTHY This study used anthropometric measurements and magnetic resonance imaging (MRI) to evaluate muscle cross-sectional area (CSA) and developed a field equation to predict thigh muscle CSA specific to the spinal cord-injured (SCI) population. Anthropometric measurements were correlated to the whole thigh CSA and muscle CSA as measured by MRI<jats:sub>.</jats:sub> The correlations led to the development of a SCI-specific field equation that accounted for intramuscular fat and bone areas. </jats:p>