To adequately evaluate the corticospinal and spinal plasticity in health and disease, it is essential to understand whether and to what extent the corticospinal and spinal responses fluctuate systematically across multiple measurements. Thus, in this study, we examined the session-to-session variability of corticospinal excitability for the ankle dorsiflexor tibialis anterior (TA) in people with and without incomplete spinal cord injury (SCI). In neurologically normal participants, the following measures were obtained across 4 days at the same time of day (N = 13) or 4 sessions over a 12-h period (N = 9, at 8:00, 12:00, 16:00, and 20:00): maximum voluntary contraction (MVC), maximum M-wave and H-reflex (M_max and H_max), motor evoked potential (MEP) amplitude, and silent period (SP) after MEP. In participants with chronic incomplete SCI (N = 17), the same measures were obtained across 4 days. We found no clear diurnal variation in the spinal and corticospinal excitability of the TA in individuals with no known neurological conditions, and no systematic changes in any experimental measures of spinal and corticospinal excitability across four measurement days in individuals with or without SCI. Overall, mean deviations across four sessions remained in a range of 5–13% for all measures in participants with or without SCI. The study shows the limited extent of non-systematic session-to-session variability in the TA corticospinal excitability in individuals with and without chronic incomplete SCI, supporting the utility of corticospinal and spinal excitability measures in mechanistic investigation of neuromodulation interventions. The information provided through this study may serve as the reference in evaluating corticospinal plasticity across multiple experimental sessions.

为了充分评估健康和疾病中的皮质脊髓和脊髓可塑性，有必要了解皮质脊髓和脊髓反应在多次测量中是否系统地波动以及在多大程度上波动。因此，在这项研究中，我们检查了有或没有不完全脊髓损伤 (SCI) 的人踝关节胫骨前背屈肌 (TA) 皮质脊髓兴奋性的会话间变异性。在神经系统正常的参与者中，在 4 天的同一时间 ( N  = 13) 或 12 小时内的 4 次会议 ( N  = 9，在 8:00、12:00、16:00)获得以下测量值和 20:00)：最大随意收缩 (MVC)、最大 M 波和 H 反射（M _max和H _max）、运动诱发电位 (MEP) 幅度以及 MEP 后的静息期 (SP)。在患有慢性不完全 SCI 的参与者 ( N  = 17) 中，在 4 天内获得了相同的测量结果。我们发现，在没有已知神经系统疾病的个体中，TA 的脊髓和皮质脊髓兴奋性没有明显的昼夜变化，并且在有或没有 SCI 的个体中，在四个测量天内脊髓和皮质脊髓兴奋性的任何实验测量值都没有系统性变化。总体而言，对于有或没有 SCI 的参与者的所有测量，四次会议的平均偏差保持在 5-13% 的范围内。该研究表明，患有或不患有慢性不完全性 SCI 的个体 TA 皮质脊髓兴奋性的非系统性会话间变异程度有限，支持皮质脊髓和脊髓兴奋性测量在神经调节干预机制研究中的实用性。通过本研究提供的信息可以作为评估多个实验过程中皮质脊髓可塑性的参考。