Relative cross-sectional areas of upper and lower extremity muscles and implications for force prediction

The purposes of this investigation were to examine the reduction in variability when muscle size is expressed relative to a functional group and its effect on improving muscle force prediction. Fourteen subjects performed maximum voluntary contractions (MVC) of elbow flexion and knee extension and had CT scans taken of the thigh and upper arm. The variation of relative cross-sectional area (RCSA) was significantly lower than CSA (p < 0.01). No significant differences were found between male and female RCSAs. A method of predicting individual muscle forces based on an MVC and RCSA is presented that reduced prediction errors to a third of those predicted on the basis of CSA and a specific tension or stress value of muscle.