Collins Brandon Wayne, Cadigan Edward W J, Stefanelli Lucas, Button Duane C
Human Neurophysiology Laboratory, School of Human Kinetics and Recreation, Memorial University, St. John's, Newfoundland and Labrador, Canada; and.
Human Neurophysiology Laboratory, School of Human Kinetics and Recreation, Memorial University, St. John's, Newfoundland and Labrador, Canada; and
J Neurophysiol. 2017 Dec 1;118(6):3242-3251. doi: 10.1152/jn.00527.2017. Epub 2017 Aug 30.
The purpose of this study was to examine the effect of shoulder position on corticospinal excitability (CSE) of the biceps brachii during rest and a 10% maximal voluntary contraction (MVC). Participants ( = 9) completed two experimental sessions with four conditions: ) rest, 0° shoulder flexion; ) 10% MVC, 0° shoulder flexion; ) rest, 90° shoulder flexion; and ) 10% MVC, 90° shoulder flexion. Transcranial magnetic, transmastoid electrical, and Erb's point stimulation were used to induce motor-evoked potentials (MEPs), cervicomedullary MEPs (CMEPs), and maximal muscle compound potentials (M), respectively, in the biceps brachii in each condition. At rest, MEP, CMEP, and M amplitudes increased ( < 0.01) by 509.7 ± 118.3%, 113.3 ± 28.3%, and 155.1 ± 47.9%, respectively, at 90° compared with 0°. At 10% MVC, MEP amplitudes did not differ ( = 0.08), but CMEP and M amplitudes increased ( < 0.05) by 32.3 ± 10.5% and 127.9 ± 26.1%, respectively, at 90° compared with 0°. MEP/M increased ( < 0.01) by 224.0 ± 99.1% at rest and decreased ( < 0.05) by 51.3 ± 6.7% at 10% MVC at 90° compared with 0°. CMEP/M was not different ( = 0.22) at rest but decreased ( < 0.01) at 10% MVC by 33.6 ± 6.1% at 90° compared with 0°. EMG increased ( < 0.001) by 8.3 ± 2.0% at rest and decreased ( < 0.001) by 21.4 ± 4.4% at 10% MVC at 90° compared with 0°. In conclusion, CSE of the biceps brachii was dependent on shoulder position, and the pattern of change was altered within the state in which it was measured. The position-dependent changes in M amplitude, EMG, and CSE itself all contribute to the overall change in CSE of the biceps brachii. We demonstrate that when the shoulder is placed into two common positions for determining elbow flexor force and activation, corticospinal excitability (CSE) of the biceps brachii is both shoulder position and state dependent. At rest, when the shoulder is flexed from 0° to 90°, supraspinal factors predominantly alter CSE, whereas during a slight contraction, spinal factors predominantly alter CSE. Finally, the normalization techniques frequently used by researchers to investigate CSE may under- and overestimate CSE when shoulder position is changed.
本研究的目的是探讨肩部位置对肱二头肌在静息状态和10%最大自主收缩（MVC）时皮质脊髓兴奋性（CSE）的影响。参与者（n = 9）完成了两个实验环节，包含四种条件：a）静息，肩部0°屈曲；b）10%MVC，肩部0°屈曲；c）静息，肩部90°屈曲；d）10%MVC，肩部90°屈曲。在每种条件下，分别采用经颅磁刺激、经乳突电刺激和Erb点刺激在肱二头肌诱发运动诱发电位（MEP）、颈髓运动诱发电位（CMEP）和最大肌肉复合电位（M）。静息时，与0°相比，90°时MEP、CMEP和M波幅分别增加（P < 0.01）509.7±118.3%、113.3±28.3%和155.1±47.9%。在10%MVC时，MEP波幅无差异（P = 0.08），但与0°相比，90°时CMEP和M波幅分别增加（P < 0.05）32.3±10.5%和127.9±26.1%。与0°相比，90°时静息状态下MEP/M增加（P < 0.01）224.0±99.1%，10%MVC时降低（P < 0.05）51.3±6.7%。静息时CMEP/M无差异（P = 0.22），但与0°相比，90°时10%MVC时降低（P < 0.01）33.6±6.1%。肌电图（EMG）在静息时增加（P < 0.001）8.3±2.0%，与0°相比，90°时10%MVC时降低（P < 0.001）21.4±4.4%。总之，肱二头肌的CSE取决于肩部位置，且变化模式在测量状态内发生改变。M波幅、EMG和CSE本身的位置依赖性变化均导致肱二头肌CSE的总体变化。我们证明，当肩部处于用于确定肘屈肌力量和激活的两个常见位置时，肱二头肌的皮质脊髓兴奋性（CSE）既取决于肩部位置也取决于状态。静息时，当肩部从0°屈曲至90°时，脊髓上因素主要改变CSE，而在轻微收缩期间，脊髓因素主要改变CSE。最后，研究人员在研究CSE时常用的标准化技术在肩部位置改变时可能会低估或高估CSE。
