Short‐interval intracortical inhibition (SICI) is often assessed to investigate inhibitory responses in the primary motor cortex representation of the quadriceps. However, determining appropriate paired‐pulse transcranial magnetic stimulation (TMS) parameters to optimise SICI measurement can be impractical and time‐consuming. This study investigated the intensity required to elicit maximal and 50% of maximum inhibition, and the test‐retest reliability of a time‐efficient approach for SICI measurement in quadriceps. Nine men and six women (26.6 ± 4.4 years) underwent single and paired‐pulse (3‐ms interval) TMS during 10% maximal voluntary isometric contraction on two days. Responses were recorded from vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM). Test stimulus intensity was 140% of active motor threshold (AMT), and conditioning stimulus intensities (CSIs) ranged from 55% to 90% (eight intensities) of AMT (five test and five paired responses for each intensity). With CSI of 55% AMT, SICI was minimal (conditioned:test motor evoked potential [MEP]; 1.00, 0.96 and 0.95 for VL, RF and VM, respectively, <1.00 indicates inhibition). Inhibition was greater at 70%–90% AMT for VL (0.67–0.85), at 75%–90% AMT for RF (0.70–0.78) and at 80%–90% AMT for VM (0.59–0.68) when compared to 55% AMT. The CSIs that elicited maximal and 50% maximal inhibition were ~84% and ~75% AMT, respectively. Reliability for individual CSIs ranged from “poor‐to‐good” for all muscles. SICI averaged across all CSIs demonstrated “moderate” reliability for VL and VM, but “poor” reliability for RF. This method may offer a practical approach to individualise and select CSIs to investigate quadriceps inhibitory networks in neurophysiological studies.

中文翻译：

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一种省时的方法来确定用于测量股四头肌短时皮质内抑制的参数。

通常评估短间隔皮质内抑制（SICI），以研究股四头肌的主要运动皮质表现形式的抑制反应。但是，确定合适的成对脉冲经颅磁刺激（TMS）参数以优化SICI测量可能是不切实际且耗时的。这项研究调查了引起最大抑制和最大抑制的50％所需的强度，以及一种用于四头肌的SICI测量的省时方法的重测信度。9名男性和6名女性（26.6±4.4岁）接受了单脉冲和成对脉冲（间隔3毫秒）的TMS，两天的最大自愿等距收缩率为10％。记录了来自股外侧肌（VL），股直肌（RF）和股内侧肌（VM）的反应。测试刺激强度为主动运动阈值（AMT）的140％，和条件刺激强度（CSI）的范围为AMT的55％至90％（八种强度）（每种强度分别进行五项测试和五对配对反应）。CSI的AMT为55％时，SICI最小（条件：测试电动机诱发电位[MEP]； VL，RF和VM分别为1.00、0.96和0.95，<1.00表示抑制）。与之相比，VL的抑制率为70％–90％（0.67–0.85），RF的抑制为75％–90％（0.70–0.78），VM的抑制率为80％–90％（0.59–0.68） 55％AMT。引起最大和最大抑制50％的CSI分别为AMT的〜84％和〜75％。单个CSI的所有肌肉的可靠性从“差”到“好”。所有CSI的SICI平均值表明VL和VM的可靠性“中等”，而RF的可靠性较差。