When we refer to “manual therapy” we usually mean mobilizations and manipulations of the spine and/or extremities. But manual therapy exists in a variety of forms and can be targeted at joints, muscles and soft tissues (as in massage or IASTM) or the neurovascular system.
Early theories on the effectiveness of those techniques in modulating a patient’s pain experience were based the identification and subsequent correction of biomechanical “dysfunctions”. You have probably read or heard about spinal alignments, subluxations, faulty positions or breaking up of supposed adhesions. However, by today’s understanding these theories are quite antiquated.
Manual therapy does not break up adhesions, it does not put a vertebra back into place, or causes other mechanical changes of that sort in the tissue it’s addressing.
So, the question remains why patients experience changes in pain intensity, improvements in range of motion due to less stiffness/tightness, and general improvement in function.
Bialosky et al (2009) and (2017) propose several theories on how manual therapy actually manages to achieve such results.
Their comprehensive model of five mechanisms suggests that a mechanical input by means of manual therapy results in a multitude of neurophysiological effects, which we will briefly discuss in this video.
Mechanical Stimulus:
Biomechanical effects of MT have been reported but these are only transient and lasting structural changes could not be identified. Furthermore, clinicians are not able to reliably determine the specific area that would require manual therapy and third the application is not precise but rather widespread which supports the notion that additional mechanisms have to be at play.
Neurophysiological Mechanism:
Hypoalgesic responses, increased sympathetic nervous system activity, and a lessening in temporal summation have been measured following the application of manual therapy. This mechanism is assumed to be mediated by the periaqueductal gray, which is an area in our brain that plays a critical role in autonomic function, motivated behavior and behavioral responses to threatening stimuli as well as changes in the spinal dorsal horn.
Peripheral Mechanism:
We know that musculoskeletal injuries result in an inflammatory response and the expression of inflammatory mediators such as blood and serum level cytokines. Studies examining the effects of joint biased manual therapy found that those were reduced following the application of manual therapy. Furthermore, they observed changes in blood levels of among others: ß-endorphin, serotonin and endogenous cannabinoids.
Spinal Mechanism:
Studies examining the spinal mechanism rely predominantly on the gate control theory where a strong enough ascending stimulus can inhibit nociceptive signals in the spinothalamic tract. Essentially the stimulation of proprioceptors leads to inhibition at the dorsal horn and associated neuromuscular responses such as hypoalgesia, afferent discharge, and changes in muscle activity occur.
Supraspinal mechanism:
Bialosky and colleagues list other variables such as the placebo effect, expectations, and psychosocial factors that are possibly relevant in explaining the effects of manual therapy. These supraspinal mechanisms were found to be associated with supraspinal descending inhibition, changes in the opioid system, and dopamine production.