Recapitulating some history
Readers other than osteopaths may ask, HVT?
So here is one definition.
High velocity refers both to the fast movement of the cavitating thrust and to the direction of that thrust.
Back in the day, we also used the term low amplitude. Our nomenclature was high-velocity, low amplitude thrust (or HVLA).
For convenience, it was shorted to HVT.
The final thrust movement has very low amplitude. There should be an inverse relationship between amplitude and speed of thrust.
What do I mean by final thrust movement?
The practitioner, having already organised the patient’s body such that there is a state of balanced ‘expectant’ tension at the target segment, makes the final, fast movement of the target joint – the ‘thrust’.
More on balanced tension below.
A basic premise is that the amount of energy we put into the patient should be no more than is necessary to complete a technique safely and effectively.
Using HVT requires the practitioner to accept several assumptions. These are;
- Intervertebral facet joints can dysfunction in a way that prevents them from moving properly, and that isolates them from adjacent segments. Let’s call them restricted joints.
- There is something that occurs during cavitation of this type of restricted joint that helps it function better, reintegrating with adjacent segments.
- HVT is a more accurate way of cavitating the restricted joint than other approaches.
Within the osteopathic profession, none of these are completely accepted. However, it is fair to say that a majority of osteopaths use the technique.
Preparing The Thrust – Two Concepts
Note that the following is the terminology I use. There isn’t a universally agreed way of describing these things.
The first way refers to the arrangement of the patient’s body such that the thrust force is directed to the target segment, as we’ve discussed above.
Take an example of L3-4 in the lumbar spine.
We balance the spine above and below this segment through combinations of opposite rotation and side-bending, one direction above, and the other below.
We should also use other accessory planes of movement. All these various planes of movement we call components. Using multiple components to zone in on the target segment is useful (though more difficult) for many reasons, one of which is that the patient feels more relaxed and – literally – less ‘wound up’.
All this to create a state of balanced tension at the target segment.
Balanced tension means that the target joint is close to cavitating.
A thrust directed at a joint that’s a long way away from its balanced tension will require a lot more energy, some of which might flow around, and not into, the target joint.
Force follows the path of least resistance, like water responds to the force of gravity.
In those few seconds before the final thrust there should be a sense that there is only a ‘little bit more to do’ and the joint we are targeting will then cavitate.
Amplification of force via leverage
Here we often use the term levers, distinguishing short-lever from long-lever.
The further away the final thrust is from the target segment, the more power is put into the segment, for any given speed.
The further away from a fulcrum you are, the more work you can do for a given amount of force. Remember the playground seesaw?
A lumbar thrust is long-lever compared to a shorter-lever cervical thrust.
So why fast?
The need for speed during efficient spinal manipulation is not to produce cavitation per se. Cavitation can happen at much lower speeds.
But more speed equals more power? Isn’t that worse?
Let’s recap some principles of physics.
The weight of the patient is equivalent to mass.
Acceleration is the rate of change of speed at any instant during the final thrust.
Distance is how far you deliver the final thrust.
Time is how long it takes to complete the final thrust.
What we are trying to achieve with a safe HVT is like a car road-test where we want to get from A to B as fast as necessary, stopping at B.
We accelerate up to the maximum speed obtained during the final thrust distance, and then rapidly decelerate.
If we have prepared the joint properly, (if you wish, refer back to here) then there is only a short distance and direction left for the joint to safely move and cavitate.
Slowly covering that remaining distance will not overcome the resistance of the segment to change. Slow speed means insufficient energy.
A faster speed overcomes resistance, resulting in successful cavitation.
Of course, one aspect of the craft of manipulation is to use the maximum necessary speed and no more.
This makes sense for many reasons, including reducing the challenge of stopping at the end point.
But there is another reason for speed that goes beyond the physics of cars and levers. Tissues aren’t rigid structures – they continuously change.
Muscle tissue will alter its tone during the technique. And non-contractile tissues may even ‘creep’ slightly if we hold the balanced tension too long.
During the technique, holding tissue tension at the target segment and in the surrounding area is like trying to focus on an erratically moving target, making it difficult to maintain the balanced tension – sometimes called the barrier tension – referred to earlier.
This is another reason why more speed helps.
Because the impulse force can flow straight and economically into the target segment before the balanced tension ‘drifts’ away, something more likely to happen in a slow speed thrust.
Done right – done wrong
Providing the acceleration and deceleration of the final thrust is controlled over a short amplitude, we achieve a safer and more effective technique than a slower speed thrust.
If we’ve arranged the patient in a comfortable way such that the target segment is balanced, and used the least leverage to achieve this result, then – despite the use of a fast final thrust with its higher level of energy – the total energy imparted to the patient during the technique is low.
If the joint is perfectly balanced before the final thrust, but the speed isn’t enough, the joint will not cavitate.
If the joint is perfectly balanced before the final thrust, but the applied distance is excessive, perhaps because the thrust has not terminated soon enough, then the joint may be irritated or even injured.
And if the joint is not correctly balanced?
Imagine it’s a long way from the state of balanced tension. For that joint to cavitate, a lot more energy has to be put into the patient’s body. Not good. And less accurate.
And if the amount of targeting or amplification used is excessive?
It’s impossible to get that state of balanced tension at the target joint. We’ve gone beyond it. The final thrust will just bounce off the patient.
We can now see that improper ways to compensate for a lack of controlled speed will likely include;
- trying to ‘lock on’ to the segment through too much targeting
- increasing amplification through excessive leverage
- using more force during the final thrust
So precise segment-level manipulation requires;
- A process and set of skills that are good enough to identify the problem joint.
- An ability to balance the segment with multiple components and minimum leverage.
- The correct choice of direction to release the segment.
- An ability to thrust across the chosen distance fast enough to achieve cavitation, but no faster.
- A definite stop point at the end of the chosen distance.
Stopping the technique is as important as starting it. Stopping the technique is an active process. A final thrust should not be allowed to ‘run out of steam’.
As an aside, there is a ‘pregnant pause’ moment, just before the final thrust, when we sense that the balance of tension is correct, we choose the precise direction of the thrust, and we visualise the speed and low amplitude of the movement.
This visualisation makes the technique work better.
The art of manipulation includes knowing when not to manipulate. Now that’s a big subject, but I mean here what joints not to manipulate. For example;
- degenerative arthrotic joints
- inflamed arthritic joints
- hypermobile joints
- tense joints
By tense joints I mean normal joints that are capable of movement but are restricted purely by muscle tension.
The distinctions between all these requires another article!
Fryette H, 1954, Principles of Osteopathic Technique, AAO, Newark
Gibbons P and Tehan P, 2001, Journal of Bodywork and Movement Therapies, April 2001, 110-119
Haas M, Journal of Manipulative and Physiological Therapies, May 1990, 204-246
Hartman L, Handbook of Osteopathic Technique, 1997, Chapman and Hall, London