Loram Ian D, Maganaris Constantinos N, Lakie Martin
Applied Physiology Research Group, School of Sport and Exercise Sciences, University of Birmingham, Birmingham, B15 2TT, UK.
J Appl Physiol (1985). 2006 Apr;100(4):1311-23. doi: 10.1152/japplphysiol.01229.2005. Epub 2005 Dec 8.
Continuous measurement of contractile length has been traditionally achieved using animal preparations in which the muscle and tendon are exposed. More modern methods, e.g., sonomicroscopy, are still invasive. There is a widely perceived need for a noninvasive, in vivo method of measuring continuous changes of human muscle contractile length. Ultrasonography has been used for several years to measure relatively static, discrete changes in tendon, aponeurosis, and muscle fascicle length. We have recently developed this technique to continuously track changes in muscle contractile length during quiet standing. Here, we present the tracking algorithm and use externally applied perturbations to establish the spatial and temporal resolution of the technique. Subjects maintained a low level of ankle torque while a pneumatic actuator applied rapid, square-pulse ankle rotations of defined magnitude and 0.2-s duration. Tracked changes in gastrocnemius and soleus contractile length follow the temporal profile of the perturbations and scale progressively (5-400 microm) with the size of the ankle rotation (0.03-0.7 degrees ). In a second experiment, we tracked a wire oscillating in water with known peak to peak amplitudes of 1.5 microm to 8 mm. The ultrasound tracking procedure had near 100% accuracy at all amplitudes for frequencies up to 3 Hz and showed attenuation at higher frequencies consistent with an effective sampling frequency of 12 Hz and sampling time of 80 ms. This noninvasive technique is sensitive, without averaging, to changes as small as 1 microm and is suitable for observing neuromotor activity in posture and locomotion.
传统上，通过暴露肌肉和肌腱的动物标本实现对收缩长度的连续测量。更现代的方法，如超声显微镜检查，仍然具有侵入性。人们普遍认为需要一种非侵入性的体内方法来测量人体肌肉收缩长度的连续变化。超声检查已被用于测量肌腱、腱膜和肌束长度的相对静态、离散变化数年。我们最近开发了这项技术，以在安静站立期间连续跟踪肌肉收缩长度的变化。在此，我们展示了跟踪算法，并使用外部施加的扰动来确定该技术的空间和时间分辨率。受试者保持低水平的踝关节扭矩，同时气动致动器施加定义幅度和0.2秒持续时间的快速方波踝关节旋转。腓肠肌和比目鱼肌收缩长度的跟踪变化遵循扰动的时间轮廓，并随着踝关节旋转大小（0.03-0.7度）逐渐缩放（5-400微米）。在第二个实验中，我们跟踪了在水中振荡的电线，其峰峰值幅度已知为1.5微米至8毫米。超声跟踪程序在高达3 Hz的频率下对所有幅度的准确率接近100%，并且在更高频率下显示出衰减，这与12 Hz的有效采样频率和80 ms的采样时间一致。这种非侵入性技术对小至1微米的变化敏感，无需平均，适用于观察姿势和运动中的神经运动活动。
