This is a famous, highly structured 8-week program divided into two 4-week phases. It utilizes high-intensity techniques to shock your metabolism, allowing you to shed fat without losing muscle mass.
To make your muscles hard and dense, you must consistently lift heavier weights or increase your workout volume over time.
According to the ACE Fitness guide on core training , developing rock-hard abs requires targeting all four major abdominal muscle groups and incorporating back stabilizers.