According Spine-health.com, the lower back is supported by the extensor, flexor and oblique muscles. As InnerBody.com explains, all of the muscles in the back, abdomen, bottom and thighs work together with the spine, connective tissues and tendons to support the lower back.
No single muscle or group of muscles can do the job on its own, and each muscle within the three groups has its own particular role. According to Spine-health.com, the erector spinae are a pair of large extensor muscles that aid in holding up the spine and supporting the gluteal muscles. The abdominal muscles belong to the flexor group and are responsible for bending, flexing and arching the lower back. The design of the oblique muscles is integral to the spine's ability to rotate without damaging the lower back.