A number of research studies have shown that psychological stress may be a risk factor for overuse and other injuries.
Cortisol is produced by the adrenal glands when we are under stress and too much cortisol can damage collagen, which is needed for tissue repair.
Another way in which psychological stress can predispose to physical injury may be through hyperventilation. When we are under stress we sometimes hyperventilate which causes vasoconstriction and an increase in body temperature. There is evidence that when heat is increased in tissues this can cause a breakdown of tendons. Maybe this means that via hyperventilation, emotional stress can be a risk factor for injury, not just in tendons but in other bodily tissues.