Kendall Tracee L, Black Christopher D, Elder Christopher P, Gorgey Ashraf, Dudley Gary A
Department of Kinesiology, The University of Georgia, Athens, GA 30605, USA.
Med Sci Sports Exerc. 2006 Aug;38(8):1470-5. doi: 10.1249/01.mss.0000228953.52473.ce.
The purpose of this study was to compare the extent of neural activation assessed by the central activation ratio (CAR) versus activation estimated from T2 magnetic resonance imaging (MRI) and neuromuscular electrical stimulation (NMES).
Seven college-age individuals volunteered for this study. CAR was determined by manually superimposing a train of NMES (50 Hz, 450-mus biphasic pulses) for 1 s during a maximal voluntary effort. The MRI-NMES method assessed activation by stimulating the knee extensors for 3 min in a 2 s on, 2 s off cycle. T2 MR images were taken at rest and after NMES was administered. Theoretical maximal torque (TMT) of the knee extensors was calculated based on the MRI-NMES activation data. The TMT was then divided by the maximal voluntary isometric contraction (MVIC) of each subject to determine the extent of neural activation during a MVIC.
The results for CAR reveal the percent activation (mean +/- SD) of the quadriceps femoris during a MVIC was 92 +/- 7% for the right thigh and 96 +/- 4% for the left thigh. The MRI-NMES method estimated that MVIC could be achieved if 75 +/- 14% of the knee extensors on the right thigh and 74 +/- 14% on the left thigh were activated. These results are similar to findings that showed MVIC could be achieved by stimulating 71% of the knee extensors.
We conclude that CAR overestimates the extent of neural activation during an MVIC because the 3D shape of the thigh is altered. This will change electric current flow to the axonal motor neuron branches and limit the artificially evoked torque, thereby resulting in an overestimation of CAR.
本研究旨在比较通过中枢激活率（CAR）评估的神经激活程度与通过T2磁共振成像（MRI）和神经肌肉电刺激（NMES）估计的激活程度。
七名大学年龄的个体自愿参与本研究。在最大自主努力期间，通过手动叠加一串NMES（50Hz，450μs双相脉冲）持续1秒来确定CAR。MRI-NMES方法通过以2秒开、2秒关的周期刺激膝伸肌3分钟来评估激活情况。在休息时和给予NMES后拍摄T2 MR图像。基于MRI-NMES激活数据计算膝伸肌的理论最大扭矩（TMT）。然后将TMT除以每个受试者的最大自主等长收缩（MVIC），以确定MVIC期间的神经激活程度。
CAR的结果显示，在MVIC期间，右大腿股四头肌的激活百分比（平均值±标准差）为92±7%，左大腿为96±4%。MRI-NMES方法估计，如果右大腿75±14%的膝伸肌和左大腿74±14%的膝伸肌被激活，就可以实现MVIC。这些结果与显示通过刺激71%的膝伸肌可实现MVIC的研究结果相似。
我们得出结论，CAR高估了MVIC期间的神经激活程度，因为大腿的三维形状发生了改变。这将改变流向轴突运动神经元分支的电流，并限制人工诱发的扭矩，从而导致对CAR的高估。
