High Velocity, Low Amplitude (HVLA) spinal manipulation is sometimes dramatically effective in relieving back pain – but not always.
HVLA has been used in physical therapy, chiropractic and osteopathy for round 150 years – and before that by bone-setters (and village blacksmiths) for many centuries.
Why HVLA is effective – and when HVLA is effective – remain a matter for conjecture?

Papers by Evans & Lucas (2010) and by Evans (2009) suggest that the mechanisms involved can commonly be described and summarised as follows:
1) A force is applied to the recipient
2) The line of action of this force is perpendicular to the articular surface of the affected joint
3) The applied force creates motion at a joint
4) This joint motion includes articular surface separation
5) Cavitation occurs within the affected joint.

The question then arises as to why cavitation (the gapping process which leads to the characteristic ‘crack’ or ‘pop’) should result in reduced pain, and/or increased range of motion?
This is particularly pertinent since before and after images (x-ray) don’t show any change of position?

Cramer et al (2010) have now offered a credible answer to at least some (the majority? all?) such events.
It seems that fibrous adhesions can form between ‘Z’ (zygapophyseal) joints during periods of relative immobility, and that these may be ‘broken’ during application of HVLA manipulation to spinal segments.

The studies that support this hypothesis involved temporary fixation of the lumbar regions of rat-spines, during which periods adhesions of varying thickness developed.
The longer the fixation (4, 8, 12, 16 weeks were tested), the larger the adhesions (see photos above).

1. Fibrous adhesions develop in hypomobile zygapophyseal joints restricting motion

2. Spinal adjustment/manipulation (HVLA) separates the articular surfaces of Z-joints by gapping them

3. This process breaks fibrous adhesions

4. Absence of adhesions allows normal motion to be resumed

Photographs of small, medium and large (rat) adhesions, between Z-joint surfaces, are shown above.

The question then arises….what happens when spinal joints are treated using other, less ‘aggressive’ methods – such as Muscle Energy Technique – where normal function frequently follows treatment?

Evans & Lucas (2010) provide one model – see the chart at the start of this post, while

Simmonds et al (2011) have offered a different – neurophysiological – model that suggests that manipulative therapies (both rapid [HVLA] and slow [MET, NAGS, SNAGS other soft tissue methods]) stimulate neural structures in fascia, and that this initiates neurophysiological responses – peripheral and central – evoking the clinical outcomes of manual therapy. These suggestions are supported by Bialowski et al (2009)

These models all include a focus on, or reference to, fascia – which is a major change from what might have been considered even 5 years ago.

The two major fascia research congresses (Boston 2007, Amsterdam 2009) have changed the landscape for clinicians – and the focus of much research.

For details of these landmark congresses, and the opportunity to purchase the proceedings books or DVDs click on the (green) links above.

For details of the next fascia congress (Vancouver 2012, click here)

As my friend Robert Schleip never tires of saying —- “fascianating times”


  • Bialowsky J et al 2009 The mechanisms of manual therapy in the treatment of musculoskeletal pain Manual Therapy 14:531–538
  • Cramer G et al 2010 Zygapophyseal joint adhesions after induced hypomobility. Journal of Manipulative and Physiological Therapeutics 33:508-518
  • Evans D 2010 Why do spinal manipulation techniques take the form they do? Towards a generalmodel of spinal manipulation Manual Therapy 15(3):212-219
  • Evans D Lucas N 2010 What is manipulation? Manual Therapy 15(3)(2010) 289-291
  • Simmonds N et al 2011 A theoretical framework for the role of fascia in manual therapy. Jnl. Bodywork & Movement Therapies IN PRESS