The most basic reason is that your arm strength is too small and you don't exercise often, which leads to weakness and pain in your arm after exercise. But the pain is normal. Just have a rest. Never mind it, never mind it. The pain of physical exercise is common. I was like you a few years ago. Not now, because I have the right. I often play basketball now. I usually go to the gym to practice. I suggest you stick to physical exercise in the future, and pay attention to exercise first. Avoid sports injuries. Pay more attention to nutrition in diet. Slowly, you will be strong. . .