MacFadden Lisa N, Brown Nicholas A T
Department of Orthopaedics, University of Utah, Salt Lake City, UT 84108, USA.
J Biomech. 2007;40(15):3448-57. doi: 10.1016/j.jbiomech.2007.05.021. Epub 2007 Jul 12.
Moment arms are important for understanding muscular behavior and for calculating internal muscle forces in musculoskeletal simulations. Biarticular muscles cross two joints and have moment arms that depend on the angle of both joints the muscles cross. The tendon excursion method was used to measure the joint angle-dependence of hamstring (biceps femoris, semimembranosus and semitendinosus) moment arm magnitudes of the feline hindlimb at the knee and hip joints. Knee angle influenced hamstring moment arm magnitudes at the hip joint; compared to a flexed knee joint, the moment arm for semimembranosus posterior at the hip was at most 7.4 mm (25%) larger when the knee was extended. On average, hamstring moment arms at the hip increased by 4.9 mm when the knee was more extended. In contrast, moment arm magnitudes at the knee varied by less than 2.8 mm (mean=1.6 mm) for all hamstring muscles at the two hip joint angles tested. Thus, hamstring moment arms at the hip were dependent on knee position, while hamstring moment arms at the knee were not as strongly associated with relative hip position. Additionally, the feline hamstring muscle group had a larger mechanical advantage at the hip than at the knee joint.
力臂对于理解肌肉行为以及在肌肉骨骼模拟中计算肌肉内力非常重要。双关节肌跨过两个关节，其力臂取决于该肌肉所跨过的两个关节的角度。采用肌腱偏移法来测量猫后肢在膝关节和髋关节处的绳肌（股二头肌、半膜肌和半腱肌）力臂大小的关节角度依赖性。膝关节角度会影响髋关节处的绳肌力臂大小；与屈膝相比，当膝关节伸直时，半膜肌后部在髋关节处的力臂最多大7.4毫米（25%）。平均而言，当膝关节更伸直时，髋关节处的绳肌力臂增加4.9毫米。相比之下，在测试的两个髋关节角度下，所有绳肌在膝关节处的力臂大小变化小于2.8毫米（平均值 = 1.6毫米）。因此，髋关节处的绳肌力臂取决于膝关节位置，而膝关节处的绳肌力臂与髋关节相对位置的关联并不那么紧密。此外，猫的绳肌群在髋关节处比在膝关节处具有更大的机械优势。
