School of Kinesiology, University of British Columbia, Vancouver, Canada.
Centre of Precision Rehabilitation for Spinal Pain, School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK.
J Physiol. 2021 May;599(9):2401-2417. doi: 10.1113/JP281145. Epub 2021 Mar 25.
Motor adaptation is thought to be a strategy to avoid pain. Current experimental pain models do not allow for consistent modulation of pain perception depending on movement. We showed that low-frequency sinusoidal stimuli delivered at painful intensity result in minimal habituation of pain perception (over 60 s) and minimal stimulation artefacts on electromyographic signals. When the amplitude of the low-frequency sinusoidal stimuli was modulated based on the vertical force participants applied to the ground with their right leg while standing upright, we demonstrated a strong association between perceived pain and motor adaptation. By enabling task-relevant modulation of perceived pain intensity and the recording electromyographic signals during electrical painful stimulation, our novel pain model will permit direct experimental testing of the relationship between pain and motor adaptation.
Contemporary pain adaptation theories predict that motor adaptation occurs to limit pain. Current experimental pain models, however, do not allow for pain intensity modulation according to one's posture or movements. We developed a task-relevant experimental pain model using low-frequency sinusoidal electrical stimuli applied over the infrapatellar fat pad. In fourteen participants, we compared perceived pain habituation and stimulation-induced artefacts in vastus medialis electromyographic recordings elicited by sinusoidal (4, 10, 20 and 50 Hz) and square electrical waveforms delivered at constant peak stimulation amplitude. Next, we simulated a clinical condition where perceived knee pain intensity is proportional to the load applied on the leg by controlling sinusoidal current amplitude (4 Hz) according to the vertical force the participants applied with their right leg to the ground while standing upright. Pain ratings habituated over a 60 s period for 50 Hz sinusoidal and square waveforms but not for low-frequency sinusoidal stimuli (P < 0.001). EMG filters removed most stimulation artefacts for low-frequency sinusoidal stimuli (4 Hz). While balancing upright, participants' pain ratings were correlated with the force applied by the right leg (R = 0.65), demonstrating task-relevant changes in perceived pain intensity. Low-frequency sinusoidal stimuli can induce knee pain of constant intensity for 60 s with minimal EMG artefacts while enabling task-relevant pain modulation when controlling current amplitude. By enabling task-dependent modulation of perceived pain intensity, our novel experimental model replicates key temporal aspects of clinical musculoskeletal pain while allowing quantification of neuromuscular activation during painful electrical stimulation. This approach will enable researchers to test the predicted relationship between movement strategies and pain.
运动适应被认为是一种避免疼痛的策略。目前的实验性疼痛模型不允许根据运动一致地调节疼痛感知。我们表明，在疼痛强度下施加低频正弦刺激会导致疼痛感知的最小习惯化（超过 60 秒），并且肌电图信号上的最小刺激伪影。当基于参与者在直立时用右腿施加到地面的垂直力来调制低频正弦刺激的幅度时，我们证明了感知疼痛和运动适应之间存在很强的关联。通过在电刺激疼痛期间启用感知疼痛强度和记录肌电图信号的与任务相关的调制，我们的新型疼痛模型将允许直接实验测试疼痛与运动适应之间的关系。
当代疼痛适应理论预测运动适应会发生以限制疼痛。然而，目前的实验性疼痛模型不允许根据姿势或运动来调节疼痛强度。我们使用施加在髌下脂肪垫上的低频正弦电刺激开发了一种与任务相关的实验性疼痛模型。在 14 名参与者中，我们比较了正弦（4、10、20 和 50 Hz）和方形电波形在恒定峰值刺激幅度下引起的股四头肌肌电图记录中的感知疼痛习惯化和刺激引起的伪影。接下来，我们模拟了一种临床情况，其中通过根据参与者在直立时用右腿施加到地面的垂直力来控制正弦电流幅度（4 Hz），使感知到的膝关节疼痛强度与施加到腿部的负荷成比例，从而控制感知到的疼痛强度。正弦（50 Hz）和方形波形的疼痛评分在 60 秒内习惯化，但低频正弦刺激（P <0.001）则不然。低频正弦刺激（4 Hz）的肌电图滤波器去除了大多数刺激伪影。在平衡直立时，参与者的疼痛评分与右腿施加的力相关（R = 0.65），证明了感知疼痛强度的与任务相关的变化。低频正弦刺激可以在 60 秒内产生恒定强度的膝关节疼痛，并且在控制电流幅度时允许与任务相关的疼痛调制，而肌电图伪影最小。通过使感知疼痛强度的任务相关调制成为可能，我们的新型实验模型复制了临床肌肉骨骼疼痛的关键时间方面，同时允许在电刺激疼痛期间量化神经肌肉激活。这种方法将使研究人员能够测试运动策略与疼痛之间的预测关系。
