So what other unsuspected things in our daily lives may cause muscle injuries that we let slide? Bad posture, lifting weights with bad form, stress, overuse, anxiety, underuse, failure to stretch after lots of contraction and even being kept in a position for too long. Of course, more serious injuries that would be obvious, such as an accident or a failure to go through rehabilitation after an injury can lead to tightness and knots. When left untreated, many people develop chronic myofascial pain.