Proper posture is standing upright, with the pelvis in line with the shoulders. The ear, shoulder, pelvis and ankle should line up in one straight line.
The first and third image shown will, in time, end up with moderate headaches, shoulder tension, knee pain, and low back pain. These symptoms can further manifest into migraines, carpal tunnel like pain, and arthritis.
Not only do these postures wear on the joints, but they cause repetitive strain injuries to the muscles which cause them to fatigue much more easily. This causes much higher likelihood that the worker will be much more tired before or after working, and thus more likely to cause mistakes or possibly injure themselves.
Let’s take a closer look at the differences between proper and poor posture.