First, find the tendon in the picture. If you look closely, you will find it. When the white tendon is separated from the red muscle, it looks like a piece.
Tendon stroke is an important reason to make abdominal muscles look piece by piece, which determines how we practice. Abdominal muscles will not just become as full as sticks like biceps brachii.
However, this thing called tendon stroke is natural and will not become more or less in your exercise.
Practitioners can usually do more supine leg lifts or suspended leg lifts. These two movements focus on stimulating the lower part of abdominal muscles, which helps people born with eight abdominal muscles to develop the last two abdominal muscles.
Practice method:
Sit-ups and leg lifts each group 10 or so, do 3 to 6 groups, and rest between each group 1 minute. If you do more than 20 supine leg lifts at a time, do suspended leg lifts. The number of groups and the number of times of each group are the same as those of supine leg lifting. If there is too much abdominal fat, you can also run to reduce fat, otherwise the excess fat will cover the abdominal muscles.