Lingering ache deep in the low back especially, after prolonged sitting or standing is due various reasons including poor posture, prolonged sitting, lack of movement due to modern lifestyle, and natural aging of the spine. The main muscle contributes to this types of lower back pain called Quadratus Lumbarum.
The rectangular muscles originate from the lower ribs and end at the top of the iliac crest of hip, is considered the main stabilizer of the spine and pelvis. As a result of instability in the hip joint or, weakness of the pelvic floor QL overworks to stabilize the spine and becomes tight and tender to the touch.
Tightness is a common protective mechanism that occurs when the body feels unstable. But since these muscles are located very deep near critical organs such as kidneys and colon, some adverse reaction might occur in these organs as well. Often, one-sided soreness in the QL is due to SI joint injury or the hyper mobility ( instability) of the SI joint or poor posture can as well be a cause of this muscle hyperactivity and fatigue as a result; carrying small object on one side also can contribute to the one-sided tightness of QL. Both sides can also get tight when the body needs to stabilize the spine on one side in an upright position, such as cycling, running, dancing.
How to release the tension of low back?
This is done by lengthening of the side of the lower back. There are few ways to stretch QL and release low back. We must understand that even though the target is one particular muscles, but these muscles are attache to bones and with fascia they have connections to other muscles, therefore always thing of the front, back and the side of the body when stretching.
Sitting on one side on your knees and while holding the foot with your hands, bending to the opposite side as far as the body allows it, ( Think of up and over as if there is a table around the bottom of your rib cage which you need to lift your body up and over that table ) make sure it doesn't cause any pain.
Another exercise that I like which activate deep Stabilizer muscles and therefore result in QL release is called:
Spine Twist Stretch
One the best way to increase range of motion and release low back is spine twist. This yoga pose is not only healthy for your spine but also, it creates movement in the bigger muscles of the back by stretching them.
Hip Flexor Stretch
Psoas Muscle is a major cause of Disc herniation, low back pain and many other issues such as Trochantric Bursitis, There are few ways that you could stretch this muscle. The one I prefer is in standing form, while one knee is down and the other leg is in 90 flexion. Common mistakes is that people bend forward and it is important to have the back straight and stretch the arm up on the side that the knee is down. I recommend holding to a stable surface such as a wall, chair so you don't have to concentrate on your balance.
Keep in mind that holding each pose for 30 seconds or longer is the key to effectively stretching a muscles.