As humans, we are influenced by internal and external factors that cause us to have emotions and feelings. When we are feeling pain inside, we naturally convey it on the outside through body language and posture.
We also perceive pain in a social context, where the behavior and reactions of people around us affects how we feel the pain. Having friends or loved ones around who can offer help and support can help alleviate pain, but how are they to know that it exists if you don't tell them?
This is where your posture comes in. You may not realize it but when you are in pain, you communicate it through body posture, which people are naturally programmed to recognize and react to. The point of any pain communication is to encourage others to help, and it seems as though body postures are a natural and effective way to get the message across.
Get the full story here: Pain communication through body posture: The many postures of pain