The decline plate sit-up is a weighted core exercise that works the rectus abdominis or "six pack" muscles, as well as the deep core muscles. Weighted sit-up variations are usually performed for moderate to high reps, such as 8-12 reps per set or more, as part of the core-focused portion of a workout.
Allows you to train in lower rep ranges when bodyweight decline sit-ups become 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
Can be progressed over time by pressing the weight overhead