Strategies that decrease lumbar compression

We have derived an equation that enumerates the variables that affect the magnitude of compressive force (F_c) on the L5-S1 joint surface:

F_c = [(F_G * s_G)*cos a] / s_M

The equation illustrates how decreased lumbar compression (F_c) results from:

1. a decrease in F_G Lift a lighter object, or lose weight ourselves. This solution, while valid, is trivial.

2. a decrease in s_G Minimize the moment arms of the two masses on which gravity acts:
   1. keep the mass you are lifting close to the body
   2. assume a posture that keeps the trunk as erect as possible. A squat lift produces smaller moments than a lifting style that involves bending over with straight knees.

3. a change in the lumbosacral angle 'a' In a squat lift, changing the pelvic tilt and the lumbar lordosis alters the angle between gravity's vertical forces and the lumbosacral joint surface. Performing a squat lift with a lumbar lordosis reduces compressive forces on the L5-S1 surface, but increases shear forces.

4. an increase in s_M develop force in structures whose moment arms (with respect to the L5-S1 joint) are as long as possible.

   Which posterior structures have the longest moment arms? How do we develop force in those structures?

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Last updated 10-30-00 ©Dave Thompson PT
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