Maas Huub, Gregor Robert J, Hodson-Tole Emma F, Farrell Brad J, Prilutsky Boris I
School of Applied Physiology, Center for Human Movement Studies, Georgia Institute of Technology, Atlanta, Georgia, USA.
J Appl Physiol (1985). 2009 Apr;106(4):1169-80. doi: 10.1152/japplphysiol.01306.2007. Epub 2009 Jan 22.
On the basis of differences in physiology, e.g., histochemical properties and spindle density, and the structural design of the cat soleus (SO) and medial gastrocnemius (MG) muscles, we hypothesized that 1) fascicle length changes during overground walking would be both muscle and slope dependent, which would have implications for the muscles' force output as well as sensory function, and that 2) muscle-tendon unit (MTU) and fascicle length changes would be different, in which case MTU length could not be used as an indicator of muscle spindle strain. To test these hypotheses, we quantified muscle fascicle length changes and compared them with length changes of the whole MTU in the SO and MG during overground walking at various slopes (0, +/- 25, +/- 50, +75, and +100%). The SO and MG were surgically instrumented with sonomicrometry crystals and fine-wire electromyogram electrodes to measure changes in muscle fascicle length and muscle activity, respectively. MTU lengths were calculated using recorded ankle and knee joint angles and a geometric model of the hindlimb. The resultant joint moments were calculated using inverse dynamics analysis to infer muscle loading. It was found that although MTU length and velocity profiles of the SO and MG appeared similar, length changes and velocities of muscle fascicles were substantially different between the two muscles. Fascicle length changes of both SO and MG were significantly affected by slope intensity acting eccentrically in downslope walking (-25 to -50%) and concentrically in upslope walking (+25 to +100%). The differences in MTU and fascicle behaviors in both the SO and MG muscles during slope walking were explained by the three distinct features of these muscles: 1) the number of joints spanned, 2) the pennation angle, and 3) the in-series elastic component. It was further suggested that the potential role of length feedback from muscle spindles is both task and muscle dependent.
基于生理学差异，例如组织化学特性和纺锤体密度，以及猫比目鱼肌（SO）和腓肠肌内侧头（MG）的结构设计，我们推测：1）在地面行走过程中，肌束长度变化将同时取决于肌肉和坡度，这将对肌肉的力输出以及感觉功能产生影响；2）肌肉-肌腱单元（MTU）和肌束长度变化会有所不同，在这种情况下，MTU长度不能用作肌肉纺锤体应变的指标。为了验证这些假设，我们量化了肌肉肌束长度变化，并将其与SO和MG在不同坡度（0、±25、±50、+75和+100%）的地面行走过程中整个MTU的长度变化进行比较。通过手术在SO和MG上植入超声晶体和细钢丝肌电图电极，分别测量肌肉肌束长度变化和肌肉活动。使用记录的踝关节和膝关节角度以及后肢的几何模型计算MTU长度。使用逆动力学分析计算产生的关节力矩，以推断肌肉负荷。结果发现，尽管SO和MG的MTU长度和速度曲线看起来相似，但两块肌肉的肌束长度变化和速度却有很大差异。在下山行走（-25至-50%）时，坡度强度对SO和MG的肌束长度变化均有显著影响，在下山行走时为离心作用，在上山行走（+25至+100%）时为向心作用。在坡度行走过程中，SO和MG肌肉的MTU和肌束行为差异可由这些肌肉的三个不同特征来解释：1）跨越的关节数量；2）羽状角；3）串联弹性成分。进一步表明，肌肉纺锤体长度反馈的潜在作用既取决于任务，也取决于肌肉。
