A worker bends over at the waist to pick up a load The angle

A worker bends over at the waist to pick up a load. The angle of flexion (w/vertical) is 130 degrees and moment arm for the muscle force is 5cm. For the geometry shown: Calculate the muscle force, compression and shear on the L_4/L_5 joint Discuss the difference between the task load and the postural load and suggest way of reducing the task load. Note that the given distances between L_4/L_5 and COGs of the upper body and load are parallel to the body, but not the ground. Remember to show you free body diagrams.

Solution

The L4/L5 joint is not shown but assume that the moments about this point by the reaction should balance the shown forces.

at angle of 130 degree the given forces have moment 150*.6 *cos40 + 400*4*cos40 = Fm*.05

Compression take components of 150N and 400 N along line at angle 50 degree,

for shear this is perpendicular to the compression force, use 40 degree angle