Final answer:
Proper upper body support when bending over involves maintaining good posture, with the center of gravity directly above the pivot point in the hips. This reduces the need for muscle action and minimizes the forces on the back. Leaning forward with an erect back and using the legs to raise the body and load helps distribute the forces and reduce strain on the back.
Step-by-step explanation:
When bending over, it is important to maintain proper upper body support to avoid back strain and damage to the disks. Good posture is key, which means standing or sitting in a way that the person's center of gravity lies directly above the pivot point in the hips. This ensures that the upper body's weight exerts no torque about the hips, reducing the need for muscle action and minimizing the forces on the back.
For example, in Figure 9.26, part (a) shows a person with good posture where the upper body's cg is directly above the hip's pivot point. However, part (b) shows bad posture where the cg is in front of the pivot, creating a clockwise torque around the hips that requires the lower back muscles to exert large forces. To maintain proper upper body support when bending over, it is important to lean forward with the back erect and use the legs to raise the body and load. This distributes the forces more evenly and reduces the strain on the back.