Elder Gabriella, Smith Samuel A, Mauger Alexis R, Norbury Ryan
Faculty of Sport, Technology and Health Sciences, St Mary's University, Twickenham, United Kingdom.
School of Natural Sciences, University of Kent, Canterbury, United Kingdom.
J Neurophysiol. 2025 Aug 1;134(2):715-727. doi: 10.1152/jn.00087.2025. Epub 2025 Jul 23.
Muscle pain can alter corticospinal function, but the specific excitatory/inhibitory effects on the quadriceps across different levels of corticospinal neuron recruitment remain unclear. Furthermore, maximal force production is reduced with muscle pain, but how the rate of force development, a key component of neuromuscular function, remains less known. To investigate this, healthy participants completed an isometric maximal voluntary contraction (MVC) followed by submaximal, intermittent contractions after receiving a hypertonic saline injection into the vastus lateralis to cause quadriceps pain (HYP), or isotonic saline, a nonpainful control (ISO). Peripheral nerve stimulation was delivered during and after MVCs to determine neuromuscular function. Transcranial magnetic stimulation (TMS) was delivered at 120% and 150% of active motor threshold during submaximal contractions to determine corticospinal excitability/inhibition, along with paired-pulse TMS to determine short-interval intracortical inhibition (SICI). Results revealed a moderate effect size (ES) reduction in MVC force (ES = -0.68, = 0.020), early-phase rate of force development (ES = -0.57, = 0.029), and voluntary activation (ES = -0.66, = 0.008) in HYP compared with ISO. Corticospinal excitability increased in HYP compared with ISO (ES = 0.60, = 0.023), whereas corticospinal inhibition decreased in HYP at higher stimulation intensities only (ES = 0.63, = 0.017). Conversely, SICI increased in HYP compared with ISO (ES = 0.58, = 0.035). Our findings indicate that muscle pain induced by a hypertonic saline injection reduced quadriceps neuromuscular function due to centrally mediated mechanisms, potentially involving both excitatory and inhibitory effects on the corticospinal tract. Hypertonic saline-induced quadriceps muscle pain reduced knee-extensor maximal voluntary force, rate of force development, and voluntary activation, without altering peripheral muscle function, suggesting a centrally mediated impairment of neuromuscular performance in healthy individuals. Alongside these changes was an increase in corticospinal excitability at both low and high stimulation intensities, whereas pain decreased corticospinal inhibition at high stimulation intensities only. Furthermore, hypertonic saline-induced pain increased intracortical inhibition, suggesting nonuniform effects of pain on the corticospinal tract.
肌肉疼痛会改变皮质脊髓功能，但在不同水平的皮质脊髓神经元募集过程中，对股四头肌的具体兴奋/抑制作用仍不清楚。此外，肌肉疼痛会降低最大力量产生，但神经肌肉功能的一个关键组成部分——力量发展速率的情况仍鲜为人知。为了对此进行研究，健康参与者在接受向股外侧肌注射高渗盐水以引发股四头肌疼痛（HYP）或注射等渗盐水（一种无痛对照，ISO）后，先完成一次等长最大自主收缩（MVC），随后进行次最大强度的间歇性收缩。在MVC期间及之后进行外周神经刺激以确定神经肌肉功能。在次最大收缩期间，以主动运动阈值的120%和150%进行经颅磁刺激（TMS），以确定皮质脊髓兴奋性/抑制，同时进行配对脉冲TMS以确定短间隔皮质内抑制（SICI）。结果显示，与ISO相比，HYP组的MVC力量（效应量[ES]= -0.68，P = 0.020）、早期力量发展速率（ES = -0.57，P = 0.029）和自主激活（ES = -0.66，P = 0.008）有中度效应量降低。与ISO相比，HYP组的皮质脊髓兴奋性增加（ES = 0.60，P = 0.023），而仅在较高刺激强度下，HYP组的皮质脊髓抑制降低（ES = 0.63，P = 0.017）。相反，与ISO相比，HYP组的SICI增加（ES = 0.58，P = 0.035）。我们的研究结果表明，高渗盐水注射诱导的肌肉疼痛通过中枢介导机制降低了股四头肌神经肌肉功能，可能涉及对皮质脊髓束的兴奋和抑制作用。高渗盐水诱导的股四头肌疼痛降低了伸膝最大自主力量、力量发展速率和自主激活，而未改变外周肌肉功能，这表明健康个体的神经肌肉性能存在中枢介导的损害。伴随这些变化的是，在低刺激强度和高刺激强度下皮质脊髓兴奋性均增加，而疼痛仅在高刺激强度下降低皮质脊髓抑制。此外，高渗盐水诱导的疼痛增加了皮质内抑制，表明疼痛对皮质脊髓束的影响不均匀。
