Final answer:
The community health nurse should instruct county office workers to sit with their back supported, keep knees at hip level, and use an ergonomically designed computer keyboard to maintain good posture and avoid back strain.
Step-by-step explanation:
A community health nurse conducting a class on body mechanics for office workers should include the following instructions: A. Sit with your back supported to provide adequate support for the spine, which maintains good posture. B. Keep your knees at hip level to ensure that your center of gravity lies directly above your hips, this avoids back strain. C.
Use an ergonomically designed computer keyboard to prevent excessive strain on your wrists and to maintain proper alignment of the upper extremities. Recommendations such as keeping the elbows away from the body and tilting the head to look at the monitor screen would not encourage proper body mechanics and should be avoided.
These guidelines are based on the principle that maintaining the body's center of gravity directly over the pivot point in the hips minimizes torque and muscle strain, especially in a sitting position, thereby preventing back strain and potential damage to spinal disks.