Bazrgari Babak, Shirazi-Adl Aboulfazl, Arjmand Navid
Department of Mechanical Engineering, Ecole Polytechnique, Montreal, QC, Canada.
Eur Spine J. 2007 May;16(5):687-99. doi: 10.1007/s00586-006-0240-7. Epub 2006 Nov 14.
Despite the well-recognized role of lifting in back injuries, the relative biomechanical merits of squat versus stoop lifting remain controversial. In vivo kinematics measurements and model studies are combined to estimate trunk muscle forces and internal spinal loads under dynamic squat and stoop lifts with and without load in hands. Measurements were performed on healthy subjects to collect segmental rotations during lifts needed as input data in subsequent model studies. The model accounted for nonlinear properties of the ligamentous spine, wrapping of thoracic extensor muscles to take curved paths in flexion and trunk dynamic characteristics (inertia and damping) while subject to measured kinematics and gravity/external loads. A dynamic kinematics-driven approach was employed accounting for the spinal synergy by simultaneous consideration of passive structures and muscle forces under given posture and loads. Results satisfied kinematics and dynamic equilibrium conditions at all levels and directions. Net moments, muscle forces at different levels, passive (muscle or ligamentous) forces and internal compression/shear forces were larger in stoop lifts than in squat ones. These were due to significantly larger thorax, lumbar and pelvis rotations in stoop lifts. For the relatively slow lifting tasks performed in this study with the lowering and lifting phases each lasting approximately 2 s, the effect of inertia and damping was not, in general, important. Moreover, posterior shift in the position of the external load in stoop lift reaching the same lever arm with respect to the S1 as that in squat lift did not influence the conclusion of this study on the merits of squat lifts over stoop ones. Results, for the tasks considered, advocate squat lifting over stoop lifting as the technique of choice in reducing net moments, muscle forces and internal spinal loads (i.e., moment, compression and shear force).
尽管人们普遍认识到提举重物在背部损伤中所起的作用，但深蹲提举与弯腰提举相比，其相对的生物力学优势仍存在争议。本研究结合体内运动学测量和模型研究，来估计在动态深蹲和弯腰提举过程中，手部有无负载时的躯干肌肉力量和脊柱内部负荷。对健康受试者进行测量，以收集提举过程中的节段旋转数据，这些数据将作为后续模型研究的输入数据。该模型考虑了脊柱韧带的非线性特性、胸段伸肌在屈曲时沿弯曲路径的包裹情况以及躯干的动态特性（惯性和阻尼），同时考虑了测量得到的运动学数据以及重力/外部负荷。采用动态运动学驱动的方法，通过同时考虑给定姿势和负荷下的被动结构和肌肉力量来解释脊柱协同作用。结果在各个水平和方向上均满足运动学和动态平衡条件。弯腰提举时的净力矩、不同水平的肌肉力量、被动（肌肉或韧带）力量以及内部压缩/剪切力均大于深蹲提举时的相应值。这是由于弯腰提举时胸部、腰部和骨盆的旋转明显更大。对于本研究中执行的相对缓慢的提举任务，下降和上升阶段各持续约2秒，一般来说，惯性和阻尼的影响并不重要。此外，弯腰提举时外部负荷相对于S1达到与深蹲提举相同力臂时的后移，并不影响本研究关于深蹲提举优于弯腰提举的结论。对于所考虑的任务，结果表明，与弯腰提举相比，深蹲提举是减少净力矩、肌肉力量和脊柱内部负荷（即力矩、压缩力和剪切力）的首选技术。
