Hanging leg and hip raise. One of the most effect core exercises. See website for details. Muscles worked: Rectus Abdominis, Iliopsoas, Tensor Fasciae Latae, Sartorius, Pectineus, Adductor Longus, Adductor Brevis, and Internal and External Obliques. Without contraction of abdomen, abs only act as synergists, and the exercise becomes just a hanging leg raise.