University of Wisconsin-Madison, 3046 Mechanical Engineering, 1513 University Ave, Madison, WI 53706 USA.
Physiol Meas. 2013 Jun;34(6):713-21. doi: 10.1088/0967-3334/34/6/713. Epub 2013 May 29.
Muscle stiffness is known to vary as a result of a variety of disease states, yet current clinical methods for quantifying muscle stiffness have limitations including cost and availability. We investigated the capability of shear wave elastography (SWE) to measure variations in gastrocnemius shear wave speed induced via active contraction and passive stretch. Ten healthy young adults were tested. Shear wave speeds were measured using a SWE transducer positioned over the medial gastrocnemius at ankle angles ranging from maximum dorsiflexion to maximum plantarflexion. Shear wave speeds were also measured during voluntary plantarflexor contractions at a fixed ankle angle. Average shear wave speed increased significantly from 2.6 to 5.6 m s(-1) with passive dorsiflexion and the knee in an extended posture, but did not vary with dorsiflexion when the gastrocnemius was shortened in a flexed knee posture. During active contractions, shear wave speed monotonically varied with the net ankle moment generated, reaching 8.3 m s(-1) in the maximally contracted condition. There was a linear correlation between shear wave speed and net ankle moment in both the active and passive conditions; however, the slope of this linear relationship was significantly steeper for the data collected during passive loading conditions. The results show that SWE is a promising approach for quantitatively assessing changes in mechanical muscle loading. However, the differential effect of active and passive loading on shear wave speed makes it important to carefully consider the relevant loading conditions in which to use SWE to characterize in vivo muscle properties.
肌肉僵硬会因多种疾病状态而变化，但目前量化肌肉僵硬的临床方法存在局限性，包括成本和可用性。我们研究了剪切波弹性成像（SWE）测量主动收缩和被动拉伸引起的跟腱剪切波速度变化的能力。 10 名健康的年轻人接受了测试。使用置于内踝跟腱上的 SWE 换能器，在从最大背屈到最大跖屈的踝关节角度范围内测量剪切波速度。还在固定的踝关节角度下测量主动跖屈肌收缩期间的剪切波速度。 随着被动背屈和伸展膝盖，平均剪切波速度从 2.6 增加到 5.6 m/s，当跟腱在弯曲膝盖的缩短姿势下时，剪切波速度不会随背屈而变化。在主动收缩期间，剪切波速度随净踝力矩单调变化，在最大收缩状态下达到 8.3 m/s。在主动和被动条件下，剪切波速度与净踝力矩之间存在线性相关性；然而，在被动加载条件下收集的数据的线性关系斜率明显更陡。 结果表明，SWE 是一种很有前途的定量评估机械肌肉负荷变化的方法。然而，主动和被动加载对剪切波速度的不同影响使得在使用 SWE 来描述体内肌肉特性时，仔细考虑相关的加载条件变得非常重要。
