Which of the following is not a characteristic of flat back posture?

A characteristic of flat back posture is the presence of a posterior pelvic tilt. In this posture, the pelvis rotates backward, leading to a flattening of the lumbar spine and reducing the natural lordotic curve. This orientation promotes a flatter appearance of the lower back, which is fundamental to recognizing flat back posture.

The other choices reference elements that typically align with a flat back posture. The extended hips and knees suggest an alignment consistent with the lack of lumbar curve seen in flat back. Additionally, the flat lower thoracic spine is also characteristic of this posture, as it often leads to an appearance of decreased thoracic kyphosis. Anterior pelvic tilt, on the other hand, involves tilting the pelvis forward and is commonly associated with excessive lumbar lordosis, which contrasts with the alignment seen in flat back posture.