This is because the upper and lower limbs are more active during exercise, and the abdominal muscles mainly play the role of driving and exerting force, with low frequency and small amplitude. In addition, bad living habits, such as eating high-fat and high-sugar foods and sitting for a long time, make a lot of fat accumulate in the abdomen, which leads to the highest hard reduction coefficient.
Therefore, if you don't want a small belly, the best way is to prevent obesity.