The Importance of Reciprocity to Human Performance

The Crossed Extensor Reflex (CER; also known as the crossed cord reflex) is a protective response that apparently begins at about the 28th week of gestation and is functionally integrated one to two month after delivery. It is functionally significant in back-and-forth (or reciprocal) muscle actions. Its dysfunction can interfere with activities like running and kicking, and other functional events. Of all the nerve signals that enter the spinal cord, 12 things happen all at the same time. Amazingly, eight of those 12 things have to do with muscles. That means that more than half of the cord responses to incoming signals have to do with muscle function. The CER response is like both the deep tendon reflex and flexor withdrawal response (FWR). Where the deep tendon reflex to the patellar tendon, for example, causes contraction of the rectus femoris, the CER inhibits the ipsilateral hamstring. (READ MORE)