Standing up, reaching for something, twisting etc., are the everyday movements we all perform. Take those movements and add jumping, hopping and turning and you now have abdominal muscles recruitment at its finest.
Abdominal muscles are the intersection of the upper and lower body.
You use them hard in a golf swing, tennis stroke and even throwing a Frisbee. There are a few areas of the mid section that you need to work to ensure balance in strength between the muscles. The rectus abdominus and the obliques. The rectus muscles are the ones that form the six pack or in some cases the eight pack of muscles in the front. The oblique area is the one termed love handles on the sides.