Final answer:
The correct principles of proper body mechanics for stooping are maintaining a straight back and lowering the center of gravity, not backward displacements. Good posture and stability are achieved through alignment of the center of gravity over the base of support.
Step-by-step explanation:
Principles of proper body mechanics include maintaining a straight back, using the legs to lift, and keeping objects close to your body. When stooping or bending, it is important to apply these principles to avoid back strain and injury. Good posture requires that the body's center of gravity be positioned above the hips to reduce the need for excessive muscle force to maintain balance. Lowering the center of gravity by bending the knees and placing the feet farther apart can increase stability. Using these techniques can reduce the forces exerted on the spine, which, unlike the hips, knees, and ankles, is relatively weak.
Backward displacement is not a principle of proper body mechanics for stooping, as it is essential to keep the center of gravity aligned with the base of support, which is achieved by leaning slightly forward, not backward. This alignment decreases the need for muscle exertion and minimizes the risk of back injuries. Therefore, the proper principle is to avoid backward displacements to maintain balance and stability during stooping activities.