Relationships between muscle architecture of rectus femoris and functional parameters of knee motion in adults with Down syndrome

This study was designed to measure in vivo muscle architecture of the rectus femoris in adults with Down syndrome, testingpossible relationships with functional parameters of the knee motion. Ten adults with Down syndrome and ten typically developedparticipated in the study. Pennation angle and thickness of the rectus femoris and subcutaneous layer of the thighweremeasured viaultrasound imaging. Knee kinematics and electromyographic activity of the rectus femoris were recorded during free leg dropping.Muscle thickness was reduced and subcutaneous layer was thicker in persons with Down syndrome with respect to typicallydeveloped adults, but there were no differences in the pennation angle. The area of the rectus femoris EMG activity during the legflexion was greater in Down syndrome with respect to typically developed adults. The leg movement velocity was lower in Downpeople than in controls, but the knee excursion was similar between the groups. Functional parameters correlated with pennationangle in the persons with Down syndrome and with muscle thickness in typically developed persons. The description of musclearchitecture and the relationships between morphological and functional parameters may provide insights on the limits and theopportunities to overcome the inherent biomechanical instability in Down syndrome.