Vastus lateralis muscle volume prediction in early-adolescent boys

The applicability of a simplified approach for muscle volume assessment, based on multiplying muscle length, maximum anatomical cross-sectional area (ACSA_max) and a muscle-specific shape factor, was investigated in the present study for the vastus lateralis muscle of early-adolescent boys. Muscle length, ACSA_max and volume were calculated from magnetic resonance image muscle reconstructions of early-adolescent athletes (n = 14) and untrained peers (n = 10). A cohort-specific shape factor was obtained from the ratio of the measured volume and the product of ACSA_max and muscle length, which did not differ significantly between trained and untrained adolescents despite significant differences in anthropometry and muscle dimensions. Further, muscle volumes assessed based on the cohort-specific shape factor did not differ significantly from the measured muscle volumes with an average root mean square difference (RMS) of 4.6%. Muscle volumes assessed with a shape factor previously reported for the vastus lateralis of adults were however significantly higher in comparison to the measured muscle volumes (P < 0.001; RMS = 8.5%). These results indicate that a cohort-specific shape factor should be applied when assessing vastus lateralis muscle volume in early-adolescents as muscle development from childhood to adulthood seems to be accompanied by changes in muscle shape.