The purpose of this study was to assess the possible role of muscles in offsetting the anterior shear forces caused by the load and upper body mass and their accelerations that act on the L 4L 5, intervertebral joint during dynamic squat lifts. Fifteen males lifted five loads from 5.8 to 32.4 kg. Anterior shear forces estimated to be acting on the lumber spine, based on model output, ranged from 492 N at 5.8 kg to 736 N at 32.4 kg. However, the peak shear force that had to be supported by the facets and possibly the disc remained relatively constant at approximately 200 N, regardless of the load mass. The posteriorly directed fascicles of the lumbar portions of the iliocostalis lumborum and longissimus thoracis muscles increased their force output, as estimated from an EMG driven model, in proportion to the anterior load shear force demands, thereby sharing the load on the intervertebral joint. It appears that the combination of anatomical design and neural control of the musculature leads to a situation where the resultant shear force on the joint can be maintained at a relatively constant and safe level in the types of lifts studied. This 'safety' mechanism is useful only with the preservation of lordosis during lifting, when the muscles must provide the majority of the support moment.

译文

:这项研究的目的是评估在动态下蹲举升过程中,肌肉在抵消由负荷和上半身及其在L 4L 5椎间关节上作用的加速度所引起的前剪切力中的可能作用。 15头雄性将五种负载从5.8公斤提升至32.4公斤。根据模型输出,估计作用在木材脊柱上的前剪力范围从5.8 kg的492 N到32.4 kg的736N。然而,无论负载质量如何,必须由刻面支撑并可能由圆盘支撑的峰值剪切力保持相对恒定,约为200N。根据肌电图驱动模型估计,the肌和腰最长肌的腰部向后束束的力输出与前部剪切力需求成正比,从而分担了椎间关节的负荷。看起来,肌肉组织的解剖学设计和神经控制的结合导致了这样一种情况,在所研究的举重类型中,在关节上产生的剪切力可以保持在相对恒定和安全的水平。这种“安全”机制仅在举重过程中保留脊柱前凸肌时有用,此时肌肉必须提供大部分的支撑力矩。

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