Abnormal posturing is an involuntary flexion or extension of the arms an legs, indicating severe brain injury. It occurs when one set of muscles becomes incapacitated while the opposing set is not, and an external stimulus such as pain causes the working set of muscles to contract. The posturing may also occur without a stimulus. Since posturing is an important indicator of the amount of damage that has occurred to the brain, it is used by medical professionals to measure the severity of a coma with the Glasgow Coma Scale (for adults) and the Pediatric Glasgow Coma Scale (for infants).