Reciprocal inhibition is a neuromuscular reflex that inhibits opposing muscles during movement. For example, contracting your elbow flexors (biceps) then your elbow extensors (triceps) are inhibited. This is the ideology behind active stretching, and one component of Proprioceptive Neuromuscular Facilitation (PNF stretching).
(Proprioceptive Neuromuscular Facilitation (PNF) is a form of flexibility training that involves stretching and contraction of the muscle group being targeted. PNF stretching was originally developed as a form of rehabilitation, and is very effective.)
Reciprocal inhibition is a neuromuscular reflex – if there is an increase in neural drive of a muscle, or group of muscles, there will be a reduction in the neural activity of functional antagonists. This is significant in improving the efficiency of the human movement system, and creating ideal arthrokinematics. This more in depth definition encompasses the role of reciprocal inhibition in more complex issues in human movement. Reciprocal inhibition is not a simple function of “on or off”, e.g. postural dysfunction will result in adaptive shortening and hypertonicity which inhibits functional antogaonists (tight gastrocnemius-inhibited foot flexors), but does not decrease the neural drive to the foot flexors complex completely making it possible to move and function (although less than optimally). Or, when looking at complex muscle synergies during tri-planal movement you may note that a muscle could be antagonists in one plane, but not another. This is important when considering any movement, however it should also be viewed in conjunction with synergistic dominance, arthrokinematic inhibition, and muscular synergies to understand the resultant effect on exercise…