Lumbar Vertebrae:

The 5 lumbar vertebrae are the largest vertebrae in the spine. They are found in the lower back, between the 12th thoracic vertebra at the base of the ribs and the sacrum in the pelvis.

The lumbar vertebrae are load bearing and balance the weight of the torso onto the sacrum. This region of the spine is quite flexible and can become over-arched and contracted (lordosis), which puts excessive pressure on the  intervertebral discs.  The discs in the lumbar region of the spine tend to be vulnerable to prolapse, or rupture,  creating severe back pain. These problems can come about because of factors such as pregnancy, poor posture, the frequent wearing of high heels and general mis-use, all of which can lead to lumbago.

For an illustration of lordosis you may visit my Blog where you will see a statue of a young woman standing with an over-arched spine.