The medicine ball zombie sit-up is a weighted exercise focusing on the abdominal muscles. It primarily targets the rectus abdominis or "six-pack" muscles, but also involves the obliques and deep core muscles. If it is too difficult with a medicine ball, it could be performed with just body weight, or with the feet anchored under a solid object.
Allows you to train in lower rep ranges when bodyweight straight-legged sit-ups get too easy
Weighted ab training can help the core muscles grow and look more defined
Also challenges the shoulders, serratus anterior, upper back, and hip flexors