A 34-year-old pregnant woman at 30 weeks gestation reports lower back discomfort, especially when standing. She denies injury, and the pain improves with rest. Which assessment finding best explains her symptoms?

Increased lumbar lordosis from the shift in the center of gravity

Decreased mobility of the sacroiliac joints

Increased thoracic kyphosis due to breast enlargement

Muscle atrophy of the paraspinal muscles from reduced activity