Neurophysiologic mechanism may underpin manual therapy effects

By Lucy Piper, Senior medwireNews Reporter

Non-thrust manual therapy (MT) may reduce chronic low-back pain (LBP) by attenuating side-to-side differences in the stretch reflex amplitude of the erector spinae muscles, study findings suggest.

The researchers, led by Brian Clark, from Ohio University in Athens, USA, observed that MT normalized stretch reflex excitability asymmetry by reducing the gain of the stretch reflex on the paraspinal side exhibiting the highest stretch reflex amplitude before treatment.

"This finding provides insight into the mechanism(s) of action of non-thrust MT, and suggests that non-thrust MT mechanistically acts by down regulating the gain of the muscle spindles and/or the various segmental sites of the Ia reflex pathway," they explain.

Clark and team note that the lack of a mechanistic underpinning has to date hindered acceptance of manual therapy by the wider scientific and healthcare communities.

"Developing a better understanding of the physiologic effects of various MTs to treat LBP will, in the long-term, assist in optimizing and developing strategic treatment strategies for specific patient populations with LBP," they believe.

A total of nine patients aged an average of 20 years with chronic LBP lasting at least 12 weeks participated in the study.

Electromechanical tapping, used to elicit short-latency stretch reflexes from the erector spinae muscles, showed a large asymmetry in the muscles before treatment, with the higher of the paraspinal sides showing a 100.2% greater value than the lower side.

After a single treatment session of non-thrust MT to the lumbar spine, however, the stretch reflex asymmetry following electromechanical tapping 10 minutes later was reduced to just 36.6%.

This change was primarily due to a significant reduction in the amplitude on the side that was higher before treatment, whereas no change over time was observed in the low side.

Also there was no longer a significant difference between the high and low sides after treatment, indicating that the asymmetry had been normalized.

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