Non-thrust manual therapy reduces erector spinae short-latency stretch reflex asymmetries in patients with chronic low back pain

The purpose of this study was to determine if non-thrust manual therapy (MT) attenuated side-to-side differences (asymmetry) of the erector spinae (ES) stretch reflex amplitude in nine patients with chronic LBP. We used electromechanical tapping to elicit short-latency stretch reflexes (SR) from the ES muscles before and after non-thrust MT. A large asymmetry in the SR was observed at baseline, with the higher of the paraspinal sides exhibiting a 100.2 ± 28.2% greater value than the lower side. Following the intervention, this SR asymmetry was reduced (100.2 ± 28.2% to 36.6 ± 23.1%; p=0.03). This change was largely due to reduced amplitude on the side that was higher at baseline (35% reduction following treatment; p=0.05), whereas no change over time was observed in the low side (p=0.23). Additionally, there was no difference between the respective sides following the intervention (p=0.38), indicating that the asymmetry was normalized following treatment. These findings provide insight into the mechanism(s) of action of non-thrust MT, and suggest that it acts to down regulate the gain of the muscle spindles and/or the various sites of the Ia reflex pathway. Ultimately, developing a better understanding of the physiologic effects of manual therapies will assist in optimizing treatment strategies for patients with LBP.