Spinal manipulative therapy: review of some proposed mechanisms, and a new hypothesis.

Some of the claims for the effects, and mechanisms for the relief of pain of spinal origin, which have been attributed to spinal manipulative therapy are reviewed. Most of these are still to be adequately investigated experimentally; the few which have been specifically investigated have not been supported. It is hypothesized that an effective, albeit often temporary, decrease in patients' perception of pain may be a result of two ordered events. The first is inhibition of reflex muscle contraction which is maximally mediated by joint afferents with end of range passive joint movement. The second is a hysteresis effect for neural discharge in joint afferents which may be produced with maintained or repetitive end of range passive joint movement.