Human Neurophysiology Laboratory, School of Human Kinetics and Recreation, Memorial University of Newfoundland , St. John's, Newfoundland , Canada.
Faculty of Medicine, Memorial University of Newfoundland , St. John's, Newfoundland , Canada.
J Neurophysiol. 2018 Dec 1;120(6):2908-2921. doi: 10.1152/jn.00358.2018. Epub 2018 Oct 24.
The present study investigated the effects of cadence and power output on corticospinal excitability to the biceps (BB) and triceps brachii (TB) during arm cycling. Supraspinal and spinal excitability were assessed using transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid electrical stimulation (TMES) of the corticospinal tract, respectively. Motor-evoked potentials (MEPs) elicited by TMS and cervicomedullary motor-evoked potentials (CMEPs) elicited by TMES were recorded at two positions during arm cycling corresponding to mid-elbow flexion and mid-elbow extension (i.e., 6 and 12 o'clock made relative to a clock face, respectively). Arm cycling was performed at combinations of two cadences (60 and 90 rpm) at three relative power outputs (20, 40, and 60% peak power output). At the 6 o'clock position, BB MEPs increased 11.5% as cadence increased and up to ~57.2% as power output increased ( P < 0.05). In the TB, MEPs increased ~15.2% with cadence ( P = 0.013) but were not affected by power output, while CMEPs increased with cadence (16.3%) and power output (up to ~19.1%, P < 0.05). At the 12 o'clock position, BB MEPs increased ~26.8% as cadence increased and up to ~96.1% as power output increased ( P < 0.05), while CMEPs decreased ~29.7% with cadence ( P = 0.013) and did not change with power output ( P = 0.851). In contrast, TB MEPs were not different with cadence or power output, while CMEPs increased ~12.8% with cadence and up to ~23.1% with power output ( P < 0.05). These data suggest that the "type" of intensity differentially modulates supraspinal and spinal excitability in a manner that is phase- and muscle dependent. NEW & NOTEWORTHY There is currently little information available on how changes in locomotor intensity influence excitability within the corticospinal pathway. This study investigated the effects of arm cycling intensity (i.e., alterations in cadence and power output) on corticospinal excitability projecting to the biceps and triceps brachii during arm cycling. We demonstrate that corticospinal excitability is modulated differentially by cadence and power output and that these modulations are dependent on the phase and the muscle examined.
本研究调查了在手臂循环过程中，步频和功率输出对肱二头肌（BB）和肱三头肌（TB）的皮质脊髓兴奋性的影响。通过经颅磁刺激（TMS）和经乳突电刺激（TMES）分别评估脊髓上和脊髓兴奋性。在手臂循环的两个位置记录 TMS 诱发的运动诱发电位（MEPs）和 TMES 诱发的颈髓运动诱发电位（CMEPs），这两个位置分别对应于肘部弯曲的中间（即，相对钟面为 6 点和 12 点）和肘部伸展的中间。手臂循环在两个步频（60 和 90 rpm）和三个相对功率输出（20、40 和 60%峰值功率输出）下进行。在 6 点位置，随着步频的增加，BB MEPs 增加了约 11.5%，随着功率输出的增加增加了约 57.2%（P < 0.05）。在 TB 中，MEPs 随步频增加约 15.2%（P = 0.013），但不受功率输出影响，而 CMEPs 随步频（约 16.3%）和功率输出（高达约 19.1%，P < 0.05）增加。在 12 点位置，随着步频的增加，BB MEPs 增加了约 26.8%，随着功率输出的增加增加了约 96.1%（P < 0.05），而 CMEPs 随步频下降约 29.7%（P = 0.013）并且不随功率输出变化（P = 0.851）。相比之下，TB MEPs 不受步频或功率输出的影响，而 CMEPs 随步频增加约 12.8%，随功率输出增加约 23.1%（P < 0.05）。这些数据表明，“类型”的强度以与相位和肌肉相关的方式差异调节脊髓上和脊髓兴奋性。新的和值得注意的是目前关于运动强度变化如何影响皮质脊髓通路内兴奋性的信息很少。本研究调查了手臂循环强度（即，步频和功率输出的改变）对在手臂循环期间投射到肱二头肌和肱三头肌的皮质脊髓兴奋性的影响。我们证明，皮质脊髓兴奋性受步频和功率输出的差异调节，并且这些调节取决于所检查的相位和肌肉。
