The most common cause of purpura on exercise is allergic purpura, when allergic purpura is in the acute phase, activity will cause the blood flow to run faster, resulting in purpura on the skin mucosa. In addition, if you have upright purpura, after standing for a long time, sudden movement can cause purpura on the skin of the lower extremities, mostly due to the fragility of the capillary walls, which is less common.