Differences in force-time parameters and electromyographic characteristics of two high-velocity, low-amplitude spinal manipulations following one another in quick succession

Cervical Multilevel

Goal of the Study?

The goal of this study 1 was to compare the force-time parameters (magnitude of a force, preload force and duration of thrusts) and electromyographic characteristics (reflex or response) between two spinal manipulations delivered following one another in quick succession if the first thrust was not associated with audible cavitation. 

Why are they doing this study?

Spinal manipulation is an effective therapy for neck and back pain and has produced an increased range of motion and a decrease in pain. But the reason for these beneficial outcomes is not well understood. Existing research suggests a relationship between spinal manipulation (thrusts) and electromyographic responses (reflexes). However, most of these studies have looked at single thrust to a thoracic vertebra using a robot or thrusts to multiple levels of the spine. Moreover, the success of a high velocity, low amplitude (HVLA) manipulation is often thought to be successful when there is cavitation (a cracking, clicking or popping sound), even though there is conflicting evidence to support this assertion.

In response to this conflicting evidence, the researchers hypothesized that there would be differences in the force-time parameters and electromyographic responses between the two thrusts. There would also be differences between people with and without symptoms.

What was done?

The researchers did two observational studies. In the first study, they recruited 9 asymptotic volunteers between 18 and 40 attending the University of Calgary. In the second study, they recruited 18 symptomatic individuals who attended a private chiropractic clinic for neck pain. 

Each participant received six diversified-style, manual HVLA spinal manipulations to the cervical and upper thoracic spines in a set order by a trained chiropractor. Electromyographic recordings were measured using surface electrodes with placement carefully matched for each participant.

What did they find?

Over fifty-two manipulations, the researchers found that peak force was higher, and the force rate was faster in the second thrust. However, they did not find any statistically significant differences for the first or second thrust between the symptomatic and asymptomatic participants. In both asymptomatic and symptomatic participants, the researchers found that the electromyographic responses were greater following the second thrust. Additionally, there were bigger differences in the responses between the two thrusts for symptomatic participants, but the degree of difference between the thrusts was larger for the asymptomatic group. 

Overall, the research results supported the original hypothesis that differences in treatment force influence electromyographic responses and electromechanical delays. Further, supporting the existing literature, the researchers found that cavitation from HVLA spinal manipulation does not cause reflex responses. 

Popping spine model


The authors note there are a few limitations that must be addressed. First, they suggest that it is difficult to know whether the second thrust’s response elicited is independent of the first thrust. Next, they suggest that it is possible the responses could be inconsistent due to electrode placement or physical differences between the participants. Finally, there could be limitations related to the study’s design. Specifically, the pressure pad is used to record the force-time parameters.

Why do these findings matter?

These findings provide some clarity of the mechanisms underlying spinal manipulation therapy as a treatment for neck pain. While further study is required, this information can be used for healthcare professionals to adjust treatment approaches. 

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