Adrenaline acts as a natural painkiller, enabling people to perform extraordinary feats—like running on broken bones—without feeling immediate pain.

Stress-induced analgesia (SIA) is a survival mechanism documented in clinical studies since the mid-20th century. When the body faces a life-threatening situation, the amygdala triggers the hypothalamus to activate the sympathetic nervous system. This release of adrenaline and norepinephrine increases heart rate and blood flow to muscles while simultaneously suppressing non-essential functions.The process involves activation of the descending pain-modulatory system. The brain releases endogenous opioids—such as endorphins and enkephalins—which bind to opioid receptors in the periaqueductal gray (PAG) area of the midbrain. This chemical reaction effectively blocks the transmission of pain signals from the spinal cord to the brain, creating a temporary state of numbness.A notable historical example occurred during the 1996 Olympic Games when gymnast Kerri Strug performed a second vault on a severely injured ankle to secure the gold medal for the United States. Medical evaluations later confirmed she had two torn ligaments and a third-degree lateral ankle sprain. Her ability to complete the movement was attributed to the massive surge of adrenaline and the resulting SIA response.Research published in journals such as Nature Neuroscience indicates that this effect is temporary, typically lasting between 10 to 60 minutes. Once the immediate threat passes and the parasympathetic nervous system takes over to restore balance, the "opioid mask" disappears. This is why athletes and accident victims often report feeling no pain until they reach safety—whether in an ambulance or locker room.