Slim, that is, close-fitting down, will be a little tight compared with ordinary down. As you said, doing dumbbell exercise is the expansion of muscle movement, which leads to the feeling of tightness. This is normal, mainly depending on whether you wear this for exercise or manual labor. If you just go shopping, it's nothing. If you want to do sports often, such as basketball and football, it is not suitable. Strenuous exercise can easily cause down jacket to tear. If you exercise more, it is recommended to change to a bigger size. For example, it's not too cold in the south, so you don't need to wear thick sweaters inside, so you don't need to change them. If you need to wear a sweater to thicken your clothes in the north, then slim clothes are not suitable, so you'd better change to a bigger size.