Abstract
BackgroundNeuromechanical responses to spinal manipulation therapy (SMT) have been shown to be modulated through the variation of SMT biomechanical parameters: peak force, time to peak force, and preload force. Although rate of force application was modulated by the variation of these parameters, the assumption that neuromuscular responses are modulated by the rate of force application remains to be confirmed. Therefore, the purpose of the present study was to evaluate the effect of a constant rate of force application in neuromechanical responses to SMT in healthy adults.MethodsFour SMT force-time profiles presenting different time to peak force and peak force, but with a constant rate of force application were applied on 25 healthy participants’ T7 transverse processes. Muscular responses were recorded through surface electromyography electrodes (T6 and T8 levels), while vertebral displacements were assessed through pasted kinematic markers on T6 to T8 spinous processes. Effects of SMT force-time profiles on neuromechanical responses were assessed using repeated-measures ANOVAs.ResultsThere was no main effect of SMT force-time profile modulation on muscular responses (ps > .05) except for the left T8 (F (3, 72) = 3.23, p = .03) and left T6 (F (3, 72) = 2.94, p = .04). Muscular responses were significantly lower for the lowest peak force condition than the highest (for T8) or second highest (for T6). Analysis showed that increasing the SMT peak force (and concomitantly time to peak force) led to a significant vertebral displacement increase for the contacted vertebra (FT7 (1, 17) = 354.80, p < .001) and both adjacent vertebras (FT6(1, 12) = 104.71, p < .001 and FT8 (1, 19) = 468.68, p < .001).ConclusionThis study showed that peak force modulation using constant rate of force application leads to similar neuromuscular responses. Coupled with previous investigations of SMT peak force and duration effects, the results suggest that neuromuscular responses to SMT are mostly influenced by the rate of force application, while peak force modulation yields changes in the vertebral displacement. Rate of force application should therefore be defined in future studies. Clinical implications of various SMT dosages in patients with spine related pain should also be investigated.Trial registrationClinicalTrials.gov NCT02550132. Registered 8 September 2015
Highlights
Neuromechanical responses to spinal manipulation therapy (SMT) have been shown to be modulated through the variation of SMT biomechanical parameters: peak force, time to peak force, and preload force
Considering the potential differences between animals, cadavers and humans responses [8], our research group has undertaken a series of experiments aimed at investigating neuromechanical responses to various SMT biomechanical parameters dosage in healthy humans through the use of an apparatus allowing the standardization of the SMT delivering
The results of the present study showed an increase in vertebral displacements when increasing SMT peak forces were applied, which is in accordance with previous studies using animal models [19,20,21]
Summary
Neuromechanical responses to spinal manipulation therapy (SMT) have been shown to be modulated through the variation of SMT biomechanical parameters: peak force, time to peak force, and preload force. Considering the potential differences between animals, cadavers and humans responses [8], our research group has undertaken a series of experiments aimed at investigating neuromechanical responses to various SMT biomechanical parameters dosage in healthy humans through the use of an apparatus allowing the standardization of the SMT delivering. These studies showed that SMT yields different vertebral displacements and local muscles activity responses depending on the dosage of the SMT peak force [9], time to peak force [10], and preload force [11]. These observations are supported by recent animal studies reporting an increased muscle spindle discharge when rate of force applications are increased [6, 12]
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