Quadratus Lumborum primarily functions as a spinal stabilizer and side bender. Lying deep in the lower back, Quadratus Lumborum's functions revolve around protecting the spine and keeping the lower back strong and healthy.
Quadratus Lumborum Muscle
Quadratus Lumborum Function - Anatomy
To understand the function of Quadratus Lumborum, it helps to first understand its anatomy and where the hell it is. As shown above, Quadratus Lumborum lies on both sides of the lumbar spine in the lower back region. Quadratus Lumborum resides underneath two large back muscle groups - the Latissimus Dorsi (Lats) and the Spinal Erectors.
Quadratus Lumborum connects from the top of the hip to the lowest rib, and also connects all along the lumbar vertebrae. These connections give Quadratus Lumborum strong leverage in side bending the torso, and also in stabilization of the spine.
Quadratus Lumborum Function 1: Spinal Stability
Quadratus Lumborum has the crucial function of protecting the lower spine from injury. Quadratus Lumborum helps keep the spine straight, neutral, and sturdy during athletic sports, lifting objects, and even while sitting in a chair. Without this function of Quadratus Lumborum, the spine would be subject to disc injuries, vertebrae fractures, and other injuries from simple active movements.
The function of spinal stability is not glamorous, but it is incredibly important. This function of Quadratus Lumborum promotes lower back durability, strength, and resilience (or lack thereof). A Quadratus Lumborum muscle that functions well in spinal stability is insurance for lower back injury prevention and also allows for a higher level of performance in physical activities. It is important to strengthen the Quadratus Lumborum through exercise in the spinal stability function - check out the 3 exercises below to train your QL to be strong, durable, and resilient in spinal stability:
Quadratus Lumborum Function 2: Side Bending
Side bending is the second main function of Quadratus Lumborum, and one that should be explored in safe ways. Side bending in isolation can be done while standing up and reaching down toward one side. If done correctly, this will trigger strong activation from Quadratus Lumborum. Be careful with this movement - it can be very beneficial but it also puts the spine in a vulnerable position. Work with a professional physical therapist or athletic trainer before doing this movement on your own, especially with weights.
Quadratus Lumborum Function 3: Causing Pain
This is not exactly a function of Quadratus Lumborum, but it is lesser known and can shed light on some lower back issues.
Since Quadratus Lumborum is so structural and functional in spinal health, it is often subject to stress and strain that can cause a lot of pain in the body. Quadratus Lumborum can get stressed and overworked during long bouts of physical activity, and then develop spasms and trigger points that can be very painful. Spasms and trigger points in Quadratus Lumborum are signals that the spine was at risk, and Quadratus Lumborum is locked up to protect it from serious injury. Check out the video below to learn more about Quadratus Lumborum muscle pain and how to alleviate it:
 Donnelly, Joseph M. Travell, Simons & Simons Myofascial Pain and Dysfunction: the Trigger Point Manual. 3rd ed., Wolters Kluwer Health, 2019.
 Davies, Clair, and Amber Davies. The Trigger Point Therapy Workbook: Your Self-Treatment Guide for Pain Relief. 3rd ed., New Harbinger Publications, Inc., 2013.