The growth of pectoral muscle is lateral growth from outside to inside. Don't worry too much. It is difficult to exercise the strength of the seam in the chest muscle, so it is more difficult to practice. At the same time, the developed middle seam requires that the pectoral muscles on both sides are very developed, so at the same time, don't stop the action training of the whole pectoral muscles such as bench press. 1, dumbbell bird, flat board, uphill and downhill; 2. Narrow push-ups; 3, parallel bars arm flexion and extension, to lower the head with chest, toes forward, upper arm extension; 4, static chest clamping, that is, hands crossed, forcibly contracting the chest muscles, forcibly squeezing to the middle, also known as crab-type chest clamping; If there are only dumbbells, you can only do these actions. Hehe, I'll tell you another way, that is, climbing the pole, which is also a way to exercise the inside of the chest muscles. However, it depends on your weight. You can try climbing the pole, because in the process of climbing the pole, your arm should hold the pole, and this circular movement depends on the inside of the chest muscle, so the effect is still good. I hope the above can help you.