Low back pain is one of the most common ailments worldwide, and its causes can range from acute injury to chronic dysfunction. Despite often being attributed to mechanical issues such as muscle strains or disc problems, the pain response in the body is primarily driven by the nervous system, which plays a complex and dynamic role in managing how we perceive and respond to pain. Understanding how the nervous system functions in response to low back pain is key to grasping the broader picture of why this condition can be so persistent and challenging to treat.
The Brain’s Prioritization: Frame, Nervous System, and Organs
The nervous system is designed to protect and maintain the most critical functions of the body, and the brain is the control center that dictates this process. When the body is threatened, the brain prioritizes protective mechanisms based on the hierarchy of systems that sustain life. The nervous system prioritizes the most essential structures — the “frame” and the vital organs — over the musculoskeletal system, which may explain why low back pain, though musculoskeletal in origin, can become a complex, system-wide issue.
Prioritizing the Frame and Nervous System
The spine, including the lower back, is a critical structure for the body’s integrity and function. It houses and protects the spinal cord, which is the main highway for the communication between the brain and the rest of the body. In the presence of low back pain, the brain perceives a potential threat to this frame, especially if there is a risk of damage to the spine or nervous tissue.
When low back pain occurs, the brain’s initial priority is to safeguard the nervous system itself. Since the spinal cord transmits information necessary for bodily functions, including motor control, sensory input, and autonomic regulation (the management of organs like the heart and lungs), the nervous system’s protection becomes a top priority.
This means the body may respond to pain with changes in movement, posture, and muscle activation to protect the spine. This protective behavior, often referred to as “guarding,” involves muscle tightness or spasms, which serve as a defense mechanism to prevent further injury. Guarding, while helpful in the short term, can exacerbate pain if prolonged, leading to secondary issues such as muscle fatigue and dysfunction.
Prioritizing the Organs
After ensuring the protection of the spinal cord and nervous system, the brain’s next priority is the health and function of vital organs, including the heart, lungs, and digestive system. While low back pain is primarily musculoskeletal, the nervous system is tightly linked to the function of internal organs. This is where the autonomic nervous system comes into play, specifically the sympathetic and parasympathetic branches.
When the body is under stress from pain, the sympathetic nervous system — often referred to as the “fight or flight” system — can become activated. This leads to a cascade of effects on the body’s organs, including increased heart rate, changes in breathing patterns, and a diversion of blood flow away from the digestive system and toward the muscles to prepare for a perceived threat. Though this response is intended to protect the body, it can worsen the experience of pain by increasing tension in the body and heightening sensitivity to painful stimuli.
In some cases, chronic low back pain can even affect the functioning of these organs, as ongoing stress on the nervous system can lead to imbalances in the autonomic nervous system. For example, people with chronic pain often experience digestive issues, cardiovascular changes, or respiratory dysfunction due to the long-term activation of the sympathetic nervous system.
The Role of the Musculoskeletal System
While the nervous system prioritizes the protection of the spine and internal organs, it also plays a significant role in how the musculoskeletal system responds to low back pain. However, because the nervous system places the preservation of critical life functions above musculoskeletal concerns, muscle and joint pain often come last in the hierarchy of protection. This can lead to a situation where the body’s response to low back pain may result in further musculoskeletal issues.
The “Guarding” Mechanism
Guarding is one of the nervous system’s primary protective strategies when it detects a threat or injury to the body, especially in the context of low back pain. The brain sends signals to the muscles surrounding the spine to contract or tighten, creating a rigid “protective shield” around the affected area. This muscle contraction is meant to limit movement and prevent further damage to the spinal structures or nervous tissue.
In the short term, guarding can be beneficial. It helps stabilize the spine and prevents actions that could exacerbate an injury. For example, if a person has a herniated disc, the body’s natural response is to tighten the surrounding muscles, limiting movement that might compress the disc further and cause more nerve irritation.
However, prolonged guarding can become problematic. When muscles are held in a state of constant contraction, they become fatigued, stiff, and less efficient at their normal functions. This can lead to secondary pain, as tight muscles press on nerves or restrict blood flow, leading to increased discomfort. Guarding can also create movement imbalances, where other parts of the body overcompensate for the limited movement in the lower back, potentially causing pain in areas such as the hips, upper back, or even the neck.
Sensitization: When Pain Becomes Chronic
One of the major challenges with low back pain is that it can become chronic, meaning that the pain persists long after the original injury has healed. This happens in part because of a process known as central sensitization, where the nervous system becomes hyper-responsive to pain signals.
In cases of chronic low back pain, the brain and spinal cord may become sensitized to pain signals, meaning they respond to even minor stimuli with heightened pain perception. For example, a small movement that would not normally cause pain may trigger a strong pain response due to this sensitization.
This process is exacerbated by the body’s continued use of the guarding mechanism, as persistent muscle tension and restricted movement can feed into the pain cycle, keeping the nervous system in a heightened state of alert. Central sensitization can also lead to a phenomenon called “referred pain,” where pain is perceived in areas of the body far from the original injury, further complicating the clinical picture.
Breaking the Cycle
To effectively manage low back pain, it’s crucial to address not just the mechanical aspects of the injury, but the nervous system’s role in pain perception and response. Treatments such as physical therapy, manual therapy, and exercises that restore movement and reduce guarding can help alleviate pain and improve function. Additionally, therapies that target the nervous system directly, such as neurofeedback, mindfulness-based stress reduction, or other pain-modulating interventions, can help to reduce central sensitization and break the chronic pain cycle.
In conclusion, low back pain is not just a musculoskeletal problem; it’s a complex issue involving the nervous system’s protective mechanisms. The brain’s prioritization of vital structures, coupled with the guarding response, plays a significant role in how pain is experienced and managed. Understanding these mechanisms provides a more holistic view of how to treat low back pain effectively and can lead to better long-term outcomes for those affected.
About the Author
Dr. Crawford earned a Doctorate of Physical Therapy from the University of Miami (FL) in 2011 and a Bachelor of Arts in Sociology from The Ohio State University in 2008. She is an active member of the American Physical Therapy Association (APTA) as well as the Ohio Physical Therapy Association (OPTA).