In humans, the S-shaped curve of the back is a natural adaptation of the erect posture, which helps minimize the energy requirements of holding the upper body erect for long periods. In fact for humans, standing is an energy-efficient posture to adopt, that requires little in metabolic cost (energy) and normal standing on both legs is almost effortless.
Most of the bones of the body are designed to aid body movement of the body parts where they are connected to each other at joints and are held together by ligaments and muscles. The main role of the ligaments is to hold the joints tightly and to resist any sideways movement that may damage them. In doing so, they tend to limit movement when a muscle is fully stretched.
The joints of the spine allow for a wide range of movements of the body such as bending forward and backward and rotational movements. The individual small bones of the spine are joined together by a series of elastic ligaments that help to maintain the normal curvature of the spine.
The human skeleton consists of two (2) lever systems, the arms and legs, joined together by an articulated column, the spine. The spine is important to maintain posture but an aching back may occur if undue strain is put on the mechanism.
More severe strain can cause damage to the muscles and to the elastic ligaments. If the strain is sudden or prolonged to the intervertebral discs, the result will be a painful back condition called the 'slipped disc'.
Standing in one particular position or in any unnatural posture for long duration could lead to discomfort, tiredness and fatigue. To maintain a standing posture for a long duration, the muscles and ligaments would experience static loading; soft tissues in the joints would experience compression, and venous pooling in the leg areas are more likely to occur. These conditions are the root causes of fatigue. If there is not enough recovery time for the muscles and the soft tissues in the joint, then fatigue would develop and cause pain.
Depending on the degree of the fatigue experienced, it may cause discomfort, distraction and possibly reduced job satisfaction and performance. Excessive fatigue may become severe with time and affect the job performance in terms of the quality of the job and the productivity. This situation may cause injury, which may lead to long term ill effects and affects the employee's general welfare.
There are jobs or tasks that are better performed in the standing posture. Wherever possible, jobs or tasks that require the person to stand still for long duration without support need redesign to allow for more postural movement and to avoid static postures. Occasions that put back/spine in an extreme postures should be avoided. Muscle fatigue may be avoided if the manner in which it arises is understood and factors that induce it are avoided.
The improper design of a standing workstation would make the task more difficult, strenuous, fatiguing, boring, unacceptable and uncomfortable for the operators, which will have an effect on quality of work, productivity and safety and health of the employees.
Source: Guidelines on Occupational Safety and Health for Standing at Work