Abstract
BackgroundWhile there is growing evidence for the efficacy of SM to treat LBP, little is known on the mechanisms and physiologic effects of these treatments. Accordingly, the purpose of this study was to determine whether SM alters the amplitude of the motor evoked potential (MEP) or the short-latency stretch reflex of the erector spinae muscles, and whether these physiologic responses depend on whether SM causes an audible joint sound.MethodsWe used transcranial magnetic stimulation to elicit MEPs and electromechanical tapping to elicit short-latency stretch reflexes in 10 patients with chronic LBP and 10 asymptomatic controls. Neurophysiologic outcomes were measured before and after SM. Changes in MEP and stretch reflex amplitude were examined based on patient grouping (LBP vs. controls), and whether SM caused an audible joint sound.ResultsSM did not alter the erector spinae MEP amplitude in patients with LBP (0.80 ± 0.33 vs. 0.80 ± 0.30 μV) or in asymptomatic controls (0.56 ± 0.09 vs. 0.57 ± 0.06 μV). Similarly, SM did not alter the erector spinae stretch reflex amplitude in patients with LBP (0.66 ± 0.12 vs. 0.66 ± 0.15 μV) or in asymptomatic controls (0.60 ± 0.09 vs. 0.55 ± 0.08 μV). Interestingly, study participants exhibiting an audible response exhibited a 20% decrease in the stretch reflex (p < 0.05).ConclusionsThese findings suggest that a single SM treatment does not systematically alter corticospinal or stretch reflex excitability of the erector spinae muscles (when assessed ~ 10-minutes following SM); however, they do indicate that the stretch reflex is attenuated when SM causes an audible response. This finding provides insight into the mechanisms of SM, and suggests that SM that produces an audible response may mechanistically act to decrease the sensitivity of the muscle spindles and/or the various segmental sites of the Ia reflex pathway.
Highlights
While there is growing evidence for the efficacy of spinal manipulation (SM) to treat Low back pain (LBP), little is known on the mechanisms and physiologic effects of these treatments
More than 25 years ago it was noticed that deep somatic or visceral pain leads to increases in muscle tone/spasm in the surrounding musculature [23], and many authors have speculated that an increased stretch reflex gain underlies the increased muscle tone in painful muscles as is commonly observed in LBP [16,17,18,24]
In addition to determining whether the motor evoked potential (MEP) and stretch reflex amplitude were altered in individuals with and without LBP, we examined whether these physiologic responses depended on whether the spinal manipulation caused an audible sound from the joint
Summary
While there is growing evidence for the efficacy of SM to treat LBP, little is known on the mechanisms and physiologic effects of these treatments. Over the past decade there has been growing scientific evidence supporting the clinical efficacy [6,7,8,9,10] and effectiveness [11,12] of manual therapies in treating LBP. The reflex activity of human back muscles has received little attention [26,27,28,29,30], and to our knowledge, no studies have quantified the effects of spinal manipulation (SM; the most common manual therapy used to treat LBP [31,32]) on the stretch reflex excitability of the low back muscles despite this being such a commonly touted mechanism of action
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