Hi Colin, petechiae and purpura both caused by bleeding under the skin but differ in size. Petechiae are smaller, pinpoint spots. Purpura are larger patches of bleeding. Despite this difference, they share many common causes and preventive approaches.is As purpura generally associated with more significant underlying medical conditions such as blood disorders, infections, or vascular problems, I will write a new article covering it. Yes, heavy lifting can cause petechiae.