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Snap, Crackle & Pop: high velocity low amplitude thrust

We need to talk about Snap, Crackle & Pop. No, not the over-sweetened cereal mascots, but the manipulation technique used to relieve back or neck pain called High Velocity Low Amplitude Thrust (HVLAT) aka HVT, adjustment, impulse, snap, crack or pop.

What’s an HVT?

Most importantly, it is a form of manual therapy proven to be an effective option for the management of various painful muscular or joint problems. 

It is the exact same phenomenon as the popping of a knuckle or an elbow, except that we have been trained to put some movement though all joints of the body, gently, safely and effectively.

It is not exclusive to osteopathy, in fact you can get cracked by a physio, chiro, trained massage therapist or even by yourself. 

Performing a ‘lumbar roll’ high velocity low amplitude thrust

What’s the pop?

The technical term for the audible pop during a manipulation is called a ‘cavitation’ – a term from physics describing the formation of vapour filled bubbles under certain pressure and speed conditions. 

In the case of human biology, we are talking about a drop in the internal pressure (where the bubble forms) within the synovial joint capsule. The bubble stays for 15-30 minutes before being reabsorbed. This time provides the joint with a easier and greater range of movement – that lovely feeling of release.

Although the sound has come to define the technique and is very satisfying to both clinician and patient, the evidence concludes that it works just as well whether you crack or not.  

How does it work?

Now how it achieves pain relief and improves movement are questions that researchers are continuing to investigate. The scientific papers are not an easy read, but the summary sounds something like this:

  • The evidence about the physiological mechanisms of this therapy is increasing, yet still limited.
  • Studies suggest the effect is achieved by a complex cascade of physical (think joints, bones, muscles) neurological (brain, neurones & nerves) and biochemical (hormones and other messengers) stimuli triggered by the manipulation.
  • Non-specific variables such as expectation of good outcome or psychological and social factors are also likely contributors to the effectiveness of this therapy.

Is it safe?

A resounding yes, but if you are a statistician, this will be a frustrating paragraph for you. 

Most published literature relating to the adverse incidence of high velocity low amplitude thrust focuses on the most serious risk from neck manipulation – stroke. There is wildly wide variation in estimated incidence of manipulation-induced stroke: 1 in 10,000 to 1 in 50,000 to 1 in 5,000,000. It is nearly impossible to reflect true incidence as estimating the true number of manipulations is almost impossible. The incidence of death by lightning is 1 in 1,000,000. Does this help?

More likely are the transient risks: local pain, headache, fatigue, radiating pain or numbness, dizziness, nausea, stiffness, hot skin, fainting. These would start within 4h & resolving within 24h – 48 hours of treatment.

There is a long list of contraindications – either absolute or relative – which your osteopath can recite even if you woke them up from the deepest sleep in the middle of the night. 

When is it useful?

Like any other technique osteopaths may use, a high velocity low amplitude thrust has its specific uses and applications which are specific to the individual. If we feel that you may benefit from this technique, we will explain why, what you can expect and ask whether you want us to go ahead or explore alternatives like soft tissue therapy, movement therapy or no treatment. 

In conclusion:

We believe that, just like the over-sweetened cereals, safety and moderation is key. Manipulative techniques do not define osteopathic care, they are one valuable tool out of many in our repertoire of approaches to helping your body restore health. 


Gyer G, Michael J, Inklebarger J, Tedla JS. Spinal Manipulation therapy: Is it all about the brain? A current review of the neurophysiological effects of spinal manipulation. J Integr Med. 2019; 17(5): 328-337

https://www.raynersmale.com/blog/2015/8/4/does-the-audible-pop-matter-the-neurophysiology-of-manipulation. Accessed 20th December 2022

Dr Gibbons and Dr Tehan Spinal Manipulation resources