Measuring mechanical properties of the vastus lateralis tendon-aponeurosis complex in vivo by ultrasound imaging

The mechanical properties of the human vastus lateralis (VL) tendon‐aponeurosis complex were investigated in eight male subjects. Knee extensor force, knee joint angle, and corresponding longitudinal VL aponeurosis displacement were monitored synchronously during graded (10‐s) maximal isometric knee extension contractions. Displacement observed during isometric conditions may be regarded as an expression of deformation in the tissues distal to the measurement site. Furthermore, aponeurosis displacement was measured during passive knee extension (90–75°°), and used to correct displacement values obtained during active contraction for joint angular motion. The passive trial yielded a highly linear relationship between aponeurosis displacement and joint angular motion (r2 = 0.998 ± 0.002) with a mean correction factor of 0.41 ± 0.10 mm/degree. Maximal knee extensor force was 5834 ± 1341 N with a corresponding VL aponeurosis displacement of 12.7 ± 2.5 mm, while correcting for joint angular motion reduced maximal displacement ∼9% (to 11.6 ± 2.5 mm, P