Three Natural Curves:
In order to assure the spine is working efficiently, we must keep the bones in the best alignment. Otherwise, the stress and forces are magnified- ligaments will be overstretched and muscles fatigued- causing pain and possible injury. In any activity, these 3 curves should be maintained- but not increased.
The head should be above the shoulders so that the ear is in-line with the top of the shoulder. The top of the shoulder should be over the hips.
For more, please visit the Health and the Workplace Center.
Source: National Institutes of Health