You can exercise with a small dumbbell or anything with a little weight.

There is an action in yoga, that is, raise your arm first, and then bend your hand back hard, but your spine must be straight.

When everyone is pushing hard and the other hand is completely relaxed, you can hold the dumbbell tightly. Because when we bend our hands hard, the joints of our hands are upside down. When we bend our hands hard, we can only stretch by lowering our muscles. But it doesn't have to be slow in the stretching process, so the effect is better. You can do this action 100 times a day, 50 times with your left hand and 50 times with your right hand. Stick to it for a while, and immediately you will see that the muscles inside the arm will gradually close.