Lesson
Loads on Spine - continued
When the spine undergoes LATERAL FLEXION and AXIAL TWISTING (as frequently seen in the golf downswing), the patterns of trunk muscle activation are far more complex than in simple flexion/extension of the spine.
[Eg.
50 Nm extension torque places 800 N COMPRESSION on L4-L5 joint BUT
50 Nm lateral flexion + axial twisting torques respectively place 1400 N and 2500N of COMPRESSION on the L4-L5 vertebral joint.]
It has been shown that spinal loading is also affected by body movement speed – rapid, jerking lifting of objects increases compressive and shear forces on the spine.
A normal or slightly flattened lumbar curve allows the lumbar muscles to partially offset the anterior shear of body weight. A lordotic lumbar curve increases loading on posterior vertebral discs and facet joints. Full lumbar flexion changes the line of action of lumbar extensor muscles do that they cannot easily counteract anterior shear.