Quadriceps (quads)

The biarticulate rectus femoris enters passive insufficiency through the completion of knee flexion when the hips are more extended or through the completion of hip extension when the knees are more flexed. The biarticulate rectus femoris enters active insufficiency through the completion of knee extension when the hips are more flexed (other heads of the quadriceps become more active) or through the completion of hip flexion when the knees are more extended (other hip flexors become more active).