It is generally accepted that spine control and stability are relevant for the prevention and rehabilitation of low back pain (LBP). However, there are conflicting results in the literature in regards to how these variables are modified in the presence of LBP. The aims of the present work were twofold: (1) to use noxious stimulation to induce LBP in healthy individuals to assess the direct effects of pain on control (quantified by the time-dependent behavior of kinematic variance), and (2) to assess whether the relationship between pain and control is moderated by psychological features (i.e. pain catastrophizing (PC) and kinesiophobia). Participants completed three conditions (baseline, pain, recovery) during a task involving completion of 35 cycles of a repetitive unloaded spine flexion/extension movement. The neuromuscular control of spine movements was assessed during each condition using maximum finite-time Lyapunov exponents (λmax). Nociceptive stimulus involved injection of hypertonic saline into the interspinous ligament, eliciting pain that was greater than baseline and recovery (p<0.001). Although there was no overall main effect of the nociceptive stimulation (i.e. pain) on λmax when the whole group was included in the statistical model (p=0.564), when data were considered separately for those with high and low PC, two distinct and well established responses to the pain were observed. Specifically, those with high PC tightened their control (i.e. stabilized), whereas those with low PC loosened their control (i.e. destabilized). This study provides evidence that individuals' beliefs and attitudes towards pain are related to individual-specific motor behaviors, and suggests that future research studying spine control/stability and LBP should account for these variables.
Keywords: Biomechanics; Kinematics; Local dynamic stability; Lyapunov exponents; Psychology.
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