Fig. 5.

The muscle ultrasound pennation angle. The figure represents a longitudinal view of quadriceps rectus femoris muscle. The pennation angle is calculated between the intercept of fascicular path to the lower aponeurosis. Additionally, the muscle length can be measured. These two variables may be used to determine the strength of the muscle, as the lower is the angle, the lower is the length, and the lower is the strength. The right panel represents a representative reduction in pennation angle after 1 week of ICU stay