I get questions from clients in passing quite often during session, classes, and so on. One I got this week was related to posture, and specifically a curved lower back, meaning the client often was mistaken for being pregnant. They asked what could be done to correct this.
A major factor of excessive curvature in the lumbar spine, more commonly known as swayback, is anterior pelvic tilt. This is generally caused from a weakness in the abdominals and hamstrings.
TFL (part of hip flexor)