“ When the central nervous system sends a message to the agonist (muscle causing movement) to contract, the tension in the antagonist (muscle opposing movement) is inhibited by impulses from motor neurons, and thus must simultaneously relax. This neural phenomenon is called reciprocal inhibition.
Taken from Massage Therapy Principles & Practices by Susan Salvo1999,pg 161
Reciprocal inhibition describes muscles on one side of a joint relaxing to accommodate contraction on the other side of that joint.
Reciprocal Inhibition, however, can backfire by both muscles attempting to contract at the same time. Thus a common tear can occur at muscle level which can cause death. The body handles this pretty well during physical activities like running, where muscles that oppose each other are engaged and disengaged sequentially to produce coordinated movement. This facilitates ease of movement and is a safeguard against injury. Sometimes, for example, a football running back can experience a "misfiring" of motor units and end up simultaneously contracting the quads and hamstrings during a hard sprint. If these muscles, which act opposite to each other are fired at the same time, at a high intensity, a tear can result. The stronger muscle, usually the quadriceps in this case, overpowers the hamstrings. This sometimes results in a common injury known as a pulled hamstring.
The term reciprocal inhibition has also been used in the literature on parallel processing and lateralization. It was used to describe the reduced activation in the less dominant hemisphere in response to lateralized stimuli during processing. This term was used in Hirnstein, Hausmann, Gunturkun's (2008) article on Functional Cerebral Asymmetries.