Although coordinated and simultaneous movement of upper- and lower-limb muscles is required for activities of daily living, interlimb neural interaction mechanisms and their nature are yet to be fully elucidated. The purpose of this study was to investigate effects of motor preparation and execution of ipsilateral, contralateral, and bilateral upper-limb muscle contractions on the excitability of corticospinal and spinal reflex circuits of the lower-limb muscles. Fourteen able-bodied individuals were recruited in each study. Experiments were conducted to investigate: (1) corticospinal excitability using transcranial magnetic stimulation applied on the primary motor cortex to evoke motor evoked potentials (MEPs); and (2) spinal reflex excitability using transcutaneous spinal cord stimulation applied at the lumbothoracic level to evoke spinal reflexes. Measurements were recorded from multiple right lower-limb muscles simultaneously during: (i) ipsilateral (right), (ii) contralateral (left), and (iii) bilateral (right and left) elbow flexion. The results indicate that MEPs in lower-limb muscles were facilitated during both preparation and execution of elbow flexion, while spinal reflexes were facilitated only during motor execution. Moreover, the extent of facilitation did not differ between right, left, and bilateral contractions. In conclusion, motor preparation for upper-limb muscle contractions did not affect spinal circuits, but seemed to affect the supraspinal networks controlling lower-limb muscles. However, actual contraction (motor execution) of upper-limb muscles is required to facilitate spinal reflex circuits controlling the lower-limb muscles. Moreover, interlimb remote facilitation in corticospinal and spinal reflex circuits did not depend on whether contralateral/ipsilateral hands were contracted or if they were contracted bilaterally.

中文翻译：

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在准备和执行等长肘关节屈曲过程中，皮质脊髓和脊髓反射回路中的肢间神经相互作用。

尽管日常生活活动需要上下肢肌肉的协调和同时运动，但肢体间神经相互作用机制及其性质尚未完全阐明。本研究的目的是研究运动准备和执行同侧、对侧和双侧上肢肌肉收缩对下肢肌肉皮质脊髓和脊髓反射回路兴奋性的影响。每项研究均招募了 14 名身体健全的人。进行实验以研究：（1）使用经颅磁刺激应用于初级运动皮层以唤起运动诱发电位（MEP）的皮质脊髓兴奋性; (2) 脊髓反射兴奋性使用经皮脊髓刺激应用于腰胸水平以唤起脊髓反射。在以下期间同时从多个右下肢肌肉记录测量值：（i）同侧（右），（ii）对侧（左）和（iii）双侧（右和左）肘关节屈曲。结果表明，在准备和执行肘关节屈曲过程中，下肢肌肉中的 MEPs 得到了促进，而脊柱反射仅在运动执行过程中得到了促进。此外，促进程度在右侧、左侧和双侧收缩之间没有差异。总之，上肢肌肉收缩的运动准备不会影响脊柱回路，但似乎会影响控制下肢肌肉的脊髓上网络。然而，需要上肢肌肉的实际收缩（运动执行）来促进控制下肢肌肉的脊髓反射回路。此外，皮质脊髓和脊髓反射回路中的肢间远程促进不取决于对侧/同侧手是否收缩或双侧收缩。