Nordez Antoine, Hug François
Laboratory Motricité, Interactions, Performance, EA 4334 University of Nantes, 25 bis Blvd. Guy Mollet, BP 72206, 44322 Nantes cedex 3, France.
J Appl Physiol (1985). 2010 May;108(5):1389-94. doi: 10.1152/japplphysiol.01323.2009. Epub 2010 Feb 18.
This pilot study was designed to determine whether the shear elastic modulus measured using supersonic shear imaging can be used to accurately estimate muscle activity level. Using direct visual feedback of torque, six healthy subjects were asked to perform two incremental isometric elbow flexions, consisting of linear torque ramps of 30 s from 0 to 40% of maximal voluntary contraction. Both electromyographic (EMG) activity and shear elastic modulus were continuously measured in the biceps brachii during the two ramps. There was significant linear regression (P<0.001) between shear elastic modulus and EMG activity level for both ramps of all six subjects (R2=0.94+/-0.05, ranging from 0.82 to 0.98). Good repeatability was found for shear elastic modulus estimated at both 3% (trial 1: 21.7+/-6.7 kPa; trial 2: 23.2+/-7.2 kPa, intraclass correlation coefficient=0.89, standard error in measurement=2.3 kPa, coefficient of variation=12.7%) and 7% (trial 1: 42.6+/-14.1 kPa; trial 2: 44.8+/-15.8 kPa, intraclass correlation coefficient=0.94, standard error in measurement=3.7 kPa, coefficient of variation=7.1%) of maximal EMG activity. The shear elastic modulus estimated at both 3 and 7% of maximal EMG activity was not significantly different (P>0.05) between the two trials. These results confirm our hypothesis that the use of supersonic shear imaging greatly improves the correlation between muscle shear elastic modulus and EMG activity level. Due to the nonlinearity of muscle mechanical properties, the muscle elasticity should be linked to the muscle stress. Therefore, the present study represents a first step in attempting to show that supersonic shear imaging can be used to indirectly estimate muscle stress.
这项初步研究旨在确定使用超声剪切成像测量的剪切弹性模量是否可用于准确估计肌肉活动水平。利用扭矩的直接视觉反馈，六名健康受试者被要求进行两次递增等长肘部屈曲，包括从0到最大自主收缩的40%的30秒线性扭矩斜坡。在两次斜坡过程中，持续测量肱二头肌的肌电图（EMG）活动和剪切弹性模量。所有六名受试者的两次斜坡的剪切弹性模量与EMG活动水平之间均存在显著线性回归（P<0.001）（R2=0.94±0.05，范围为0.82至0.98）。在最大EMG活动的3%（试验1：21.7±6.7kPa；试验2：23.2±7.2kPa，组内相关系数=0.89，测量标准误差=2.3kPa，变异系数=12.7%）和7%（试验1：42.6±14.1kPa；试验2：44.8±15.8kPa，组内相关系数=0.94，测量标准误差=3.7kPa，变异系数=7.1%）时估计的剪切弹性模量具有良好的重复性。两次试验之间，在最大EMG活动的3%和7%时估计的剪切弹性模量无显著差异（P>0.05）。这些结果证实了我们的假设，即使用超声剪切成像可大大改善肌肉剪切弹性模量与EMG活动水平之间的相关性。由于肌肉力学特性的非线性，肌肉弹性应与肌肉应力相关联。因此，本研究是试图表明超声剪切成像可用于间接估计肌肉应力的第一步。
