The multifidus muscles are key stabilizers of the spine, playing an essential role in maintaining posture, providing core stability, and supporting coordinated movement. Recent research suggests a growing trend in the accumulation of fat within these muscles, a phenomenon known as muscle fatty infiltration or lipomatosis. Historically, such changes were observed mainly in aging populations or in those with specific pathological conditions like low back pain (LBP) or spinal disorders. However, increasingly, it appears that fatty infiltration of the multifidus is becoming more common across a broader segment of the population, even among those without overt clinical pathology. This review aims to explore the reasons behind this shift in the health and composition of the multifidus muscles.‍

Modern Sedentary Lifestyles

One of the most significant factors contributing to fatty infiltration of the multifidus muscles is the rise of sedentary behavior in modern society. As technology has advanced, the amount of time spent in seated positions—such as at desks, in front of computers, and on mobile devices—has greatly increased. This sedentary lifestyle leads to a decline in muscle activity and a reduction in the natural demand on stabilizing muscles, including the multifidus. When muscles are not regularly activated or subjected to load-bearing activity, they can undergo atrophy (shrinking of muscle fibers), and fatty infiltration can occur as a compensatory process.‍

Reduced Physical Activity and Muscle Atrophy

Physical inactivity contributes not only to the atrophy of muscles but also to changes in muscle composition. Studies show that muscle mass declines with age and physical inactivity, leading to a loss of lean muscle fibers and their replacement by fat cells. This replacement is not limited to large muscle groups like the quadriceps but extends to smaller muscles such as the multifidus, which are essential for spinal stabilization. The multifidus, being a deep stabilizer muscle, is particularly vulnerable to disuse atrophy, and fat infiltration serves as a substitute in the absence of functional muscle tissue.‍

Increased Prevalence of Low Back Pain

Low back pain (LBP) is one of the most common musculoskeletal conditions worldwide. A well-documented association exists between LBP and fatty infiltration of the multifidus muscles, particularly in individuals with chronic pain. The relationship is bidirectional: chronic pain leads to disuse and weakening of the multifidus muscles, while fat infiltration may further impair muscle function and contribute to pain persistence. This cycle may explain the increasing occurrence of fatty infiltration in people experiencing chronic back pain, even when other structural causes are not present. Additionally, people with LBP often engage in protective muscle guarding or altered postures, further contributing to muscle dysfunction and fat replacement.‍

Aging and Degenerative Processes

As individuals age, muscle mass naturally decreases, and the composition of muscle tissue changes. This is part of a broader phenomenon called sarcopenia, where there is a progressive loss of skeletal muscle mass and strength. In older adults, the multifidus muscles are particularly prone to fatty infiltration as the body struggles to maintain lean muscle tissue. Fatty infiltration is also linked to the degenerative changes in the spine, including disc degeneration, facet joint arthritis, and general spinal stiffness. As the body ages, the multifidus muscles become less efficient in maintaining proper spinal alignment, leading to increased susceptibility to further muscle degeneration and fatty infiltration.‍

Metabolic and Nutritional Factors

Changes in diet and metabolism may also influence muscle composition. Poor nutrition, particularly diets high in processed foods and low in essential nutrients like protein, can hinder muscle repair and regeneration, exacerbating the process of fatty infiltration. Additionally, metabolic conditions such as obesity and insulin resistance can promote the accumulation of fat within muscles, including the multifidus. Fatty infiltration may thus be linked to broader systemic issues, including poor metabolic health, which is increasingly prevalent in modern society due to lifestyle factors such as poor diet and insufficient physical activity.‍

Impaired Neuromuscular Control

The multifidus muscles rely on the central nervous system for precise and coordinated activation. Research indicates that individuals with impaired neuromuscular control—such as those with certain neurological disorders or musculoskeletal conditions—are more likely to experience fatty infiltration in the multifidus. Decreased motor control or inefficient activation of these deep spinal stabilizers leads to disuse and muscle atrophy, which may ultimately contribute to fat replacement.‍

Genetic and Epigenetic Factors

There is evidence to suggest that genetic predispositions can play a role in how the body responds to physical inactivity, aging, and injury. Certain individuals may be genetically predisposed to a higher likelihood of fatty infiltration in muscle tissue. Additionally, epigenetic factors—changes in gene expression caused by lifestyle factors like diet, exercise, and stress—can influence how muscle tissues adapt to environmental conditions, including the accumulation of fat in muscles like the multifidus.‍

Muscle Regeneration and Fat Infiltration

Fat infiltration in muscles is not necessarily a passive process. Some researchers suggest that fat may infiltrate muscle tissue as part of a compensatory regenerative process following injury or disuse. In the case of the multifidus muscles, which are prone to atrophy due to their stabilizing role, fat may fill the space vacated by degenerating muscle fibers. This process could be seen as an adaptive mechanism, though it ultimately leads to a decrease in muscle function, endurance, and the ability to provide spinal stability.

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The increasing prevalence of fatty infiltration in the multifidus muscles of the spine is a multifactorial phenomenon, influenced by modern sedentary lifestyles, aging, chronic low back pain, metabolic conditions, and impaired neuromuscular function. While fatty infiltration was once largely confined to older adults or those with chronic spinal conditions, it is now becoming more common in the general population. Understanding these trends is crucial for developing preventive and rehabilitative strategies to maintain spinal health and function, which may include promoting physical activity, improving posture, and addressing metabolic health. As research into muscle degeneration and regeneration continues, targeted interventions that preserve muscle integrity and prevent fatty infiltration in the multifidus will become increasingly important in combating the growing burden of musculoskeletal dysfunction in modern society.

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