📌The synergistic action between a representative abdominal muscle [rectus abdominis] and the iliopsoas and rectus femoris is illustrated while performing a straight-leg raise.
(a) Sufficient activation of the abdominal muscles opposes the strong downward pull of the hip flexor muscles, preventing an anterior tilt of the pelvis.
(b) With reduced activation of the abdominal muscles, contraction of the hip flexor muscles is shown producing a marked anterior tilt of the pelvis—increasing the lumbar lordosis. The reduced activation in the abdominal muscle is indicated by the lighter red color.
📌Source
https://link.springer.com/chapter/10.1007/978-1-4614-0694-5_5#citeas