You can exercise the pectoralis major. How much you do depends on your personal situation. Do it in groups. Keep exercising, and you will grow chest muscles. Dumbbell arm up
Dumbbell single arm bending
Sit on dumbbells and bend alternately
Flexion and extension of one-arm dumbbell neck and back arm
They all exercise their arms. Keep exercising and your arm strength will improve. You can do it in groups until you are exhausted, that is, you can't do it anymore. Just do four or five groups.
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