Figure 1. Ultrasonic images of the longitudinal sections of the vastus lateralis muscle at rest (A) and during isometric 50 % MVC contraction (B).

The point at which one fascicle was attached to the deep aponeurosis was defined as P. A marker (X) was placed between the skin and the ultrasonic probe as an indicator to confirm that the probe did not move during measurements. The cross-point between the superficial aponeurosis and fascicles did not move. Therefore, the distance travelled by P (P₂– P₁) was defined as the length change of the tendon and aponeurosis during contraction. VL, m. vastus lateralis; VI, m. vastus intermedius.