@posturemanual: Straight Back Thoracic, Flat Back, Common Muscle Imbalance. #posture #posturecorrection #posturetips #flatback #thoracicspine EXAMPLE: Straightened curvature of the thoracic spine when standing or walking. Common in adolescents, or underweight people. Due to a wrong sense of core muscle control, when trying to keep the body "sitting up straight" and overly straighten the upper back for a long period and other movement habits. This results in excessive tension in the middle back, lower back, and related muscles over a long period. If an upright posture makes you feel confident, follow the subsequent breathing-related topics to learn how to properly control the middle of your torso and straighten your upper back within a more reasonable range.