Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo, 153-8902, Japan.
Japan Society for the Promotion of Science, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo, 102-0083, Japan.
Exp Brain Res. 2020 Sep;238(9):1977-1987. doi: 10.1007/s00221-020-05857-0. Epub 2020 Jun 26.
Ankle dorsiflexion force control is essential for performing daily living activities. However, the involvement of the corticospinal pathway during different ankle dorsiflexion tasks is not well understood. The objective of this study was to compare the corticospinal excitability during: (1) unilateral and bilateral; and (2) ballistic and tonic ankle dorsiflexion force control. Fifteen healthy young adults (age: 25.2 ± 2.8 years) participated in this study. Participants performed unilateral and bilateral isometric ankle dorsiflexion force-control tasks, which required matching a visual target (10% of maximal effort) as quickly and precisely as possible during ballistic and tonic contractions. Transcranial magnetic stimulation (TMS) was applied over the primary motor cortex to elicit motor-evoked potentials (MEPs) from the right tibialis anterior during: (i) pre-contraction phase; (ii) ascending contraction phase; (iii) plateau phase (tonic tasks only); and (iv) resting phase (control). Peak-to-peak MEP amplitude was computed to compare the corticospinal excitability during each experimental condition. MEP amplitudes significantly increased during unilateral contraction compared to bilateral contraction in the pre-contraction phase. There were no significant differences in the MEP amplitudes between the ballistic tasks and tonic tasks in any parts of the contraction phase. Although different strategies are required during ballistic and tonic contractions, the extent of corticospinal involvement appears to be similar. This could be because both tasks enhance the preparation for precise force control. Furthermore, our results suggest that unilateral muscle contractions may largely facilitate the central nervous system during movement preparation for unilateral force control compared to bilateral muscle contractions.
踝关节背屈力控制对于进行日常活动至关重要。然而，皮质脊髓通路在不同的踝关节背屈任务中的参与情况尚不清楚。本研究的目的是比较在以下情况下皮质脊髓兴奋性的差异：（1）单侧和双侧；（2）弹性能量和强直性能量踝关节背屈力控制。15 名健康的年轻成年人（年龄：25.2±2.8 岁）参与了这项研究。参与者进行了单侧和双侧等长踝关节背屈力控制任务，需要在弹性能量和强直性能量收缩过程中尽可能快速和精确地匹配视觉目标（最大努力的 10%）。经颅磁刺激（TMS）应用于初级运动皮层，在以下情况下从右侧胫骨前肌引出运动诱发电位（MEPs）：（i）预收缩阶段；（ii）上升收缩阶段；（iii）平台阶段（仅强直任务）；和（iv）休息阶段（对照）。计算峰峰值 MEP 幅度，以比较每个实验条件下的皮质脊髓兴奋性。与双侧收缩相比，在预收缩阶段，单侧收缩时 MEP 幅度明显增加。在收缩阶段的任何部分，弹性能量任务和强直任务之间的 MEP 幅度均无显著差异。尽管在弹性能量和强直收缩过程中需要不同的策略，但皮质脊髓的参与程度似乎相似。这可能是因为这两种任务都增强了对精确力控制的准备。此外，我们的结果表明，与双侧肌肉收缩相比，单侧肌肉收缩在单侧力控制的运动准备过程中可能在很大程度上促进了中枢神经系统。
