[matheusmoreira]

Depends on the job and the ergonomics involved but in general: posture. Most people just have really bad posture in general. Even while standing or sitting.

There are proper postures to do a lot of activities and they are frequently not observed. Maintaining proper posture is a skill that must be trained until you don't have to think about it. Even something "mindlessly simple" like lifting a heavy object off the ground and carrying it somewhere requires proper posture and technique to reduce chance of injuries. Reduce, not eliminate. You can do everything right and still get injured.

When lifting things off the ground, most people will flex and extend the torso instead of using their much stronger leg muscles. The better form is to squat down by flexing the thighs, pick up the object then lift it up by extending the thighs, all while maintaining the spine aligned.

Physical education and conditioning is important in these jobs. In our every day lives.