By Lucy Piper, Senior medwireNews Reporter
Instrument-assisted spinal manipulative therapy (SMT) targeted to the low-back region has an immediate and widespread hypoalgesic effect, say researchers.
Although their study involved asymptomatic participants, the team says the findings "add weight to the understanding of possible involvement of neurophysiologic mechanisms."
The researchers found there was an approximate 15% change in pressure pain thresholds (PPTs) following instrument-assisted SMT, which they believe is enough to suggest it has the capacity to produce hypoalgesia in the absence of pain for asymptomatic participants.
"Potentially, a greater response to lumbar instrument-assisted SMT may occur in symptomatic participants," say Xiangrui Wang (Renji Hospital, Shanghai, China) and colleagues.
The study, published in the Journal of Manipulative and Physiological Therapeutics, involved 30 participants (19 men and 11 women) without a current history of lower back pain.
Each participant attended two treatment group sessions and was randomly assigned to receive instrument-assisted SMT or a sham manipulation therapy. Instrument-assisted SMT was administered using the Activator Method protocol.
PPT measures increased significantly and immediately in the participants after receiving instrument-assisted SMT, irrespective of the site treated.
Specifically, PPT over the L5 zygapophyseal joints increased by 16.6% and 12.0% from baseline for the pelvic deficient and opposite pelvic deficient sides, respectively, and by a corresponding 14.8% and 16.1% in the L5 dermatomes, and 15.96% and 16.8% in the hand.
There was no increase in PPT measures for participants receiving the sham manipulation therapy.
"Owing to the small sample size, the results should be interpreted with some caution," the researchers warn.
"However, our results indicate that changes after manipulation are systemic, irrespective of the different sites measured or treated, which suggests the possible activation of the central nervous system involving the descending pain inhibitory pathways, which extends beyond the specific joints and spinal segments stimulated."
They also note that there was an immediate muscle relaxation effect after instrument-assisted SMT, according to basal electromyographic activity measurements, but this effect was localized, occurring only at the treated site.
This muscle relaxation was not related to the increases in PPT, which suggests that the "effects of pain sensitivity and muscle relaxation may share different mechanisms," the researchers explain.
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