A study has shown that criticism while doing physical labor can not only affect our feelings, but also can cause more back pain. "Psychological stress seems to amplify the physical demands of lifting for certain personality types," the study found.
The study involved asking volunteers to lift a 25-pound box. While they did so, they were either encouraged, or criticized with statements like "You can do better than that!"
Certain personality types actually showed more spinal compression and strain while being criticized. "Introverts changed the way they used their muscles, so that lifting became much more mechanically stressful," commented a researcher.