Possibility 1: Whether the clothes worn during exercise are more suitable, it is better to use cotton texture and be loose.

Possibility 2: Blood circulation accelerates during exercise, and capillaries expand rapidly, resulting in local hypoxia or small red lines on the skin. It is suggested to exercise scientifically, and you can make appropriate adjustments with reference to your own exercise heart rate. Don't exercise too hard, do some relaxation exercises before exercise.

Possibility 3: Go to the hospital to see a dermatologist.

They are more likely, so it is helpful to pay attention to reasonable and scientific fitness.