Uterine fibroids are non-cancerous growths that form within the muscular wall of the uterus, commonly affecting women during their reproductive years. These growths vary in size and number, sometimes leading to symptoms. A concern that arises with fibroids is degeneration, a process where the growth begins to break down. Does high-volume exercise, such as running, cause or accelerate this fibroid degeneration?
What Uterine Fibroids Are
Uterine fibroids, medically known as leiomyomas or myomas, are solid tumors that originate from the smooth muscle tissue of the uterus, called the myometrium. Fibroids are extremely common, with most women developing them at some point, although many remain unaware because the growths are too small or asymptomatic.
Their location determines their classification, which includes intramural (within the uterine wall), submucosal (bulging into the uterine cavity), and subserosal (on the outer surface of the uterus). Depending on their position and size, fibroids can lead to various symptoms, such as heavy or prolonged menstrual bleeding, which can sometimes lead to anemia, and pelvic pressure or pain.
The Medical Process of Fibroid Degeneration
Fibroid degeneration is a biological process where the tissue within the tumor begins to die, or undergo necrosis, primarily due to an inadequate blood supply. As a fibroid grows, it develops its own network of blood vessels, but the tumor often outpaces the body’s ability to supply sufficient oxygen and nutrients. This tissue breakdown is a reaction to internal vascular insufficiency, not an external traumatic event.
The most common form is hyaline degeneration, where the smooth muscle tissue is replaced by a glassy, protein-like material; this type is often asymptomatic. Another notable form is red degeneration, or hemorrhagic infarction, which occurs when a sudden lack of blood flow causes acute pain and is seen most frequently during pregnancy. Degeneration can also manifest as cystic or myxoid changes, where fluid-filled sacs or a gelatinous material accumulate within the fibroid tissue. While degeneration can sometimes lead to shrinkage and symptom relief, the acute phase is characterized by sudden, severe pain.
Evaluating the Link Between Running and Degeneration
The scientific consensus does not support the idea that high-volume running or other forms of vigorous exercise cause fibroid degeneration. Degeneration is firmly rooted in the tumor’s internal biology and its failure to maintain its blood supply, which is not triggered by physical activity. The acute pain associated with degeneration is a result of tissue necrosis, not a mechanical injury from running.
Regular exercise is often recommended for individuals with fibroids because it supports overall uterine health. Physical activity helps maintain a healthy body weight, and studies suggest that a lower Body Mass Index (BMI) is associated with a reduced risk of fibroid growth. Furthermore, cardiovascular exercise helps regulate hormone levels, specifically reducing circulating estrogen and progesterone, which fuel fibroid development.
While running temporarily increases blood flow throughout the body, including the pelvic region, this effect is generally considered beneficial for systemic health. It does not typically initiate the localized vascular crisis required for degeneration.
For most people, running is safe and should be continued, offering benefits such as improved cardiovascular health and hormonal balance. The main limitations runners with fibroids face are symptomatic, such as increased fatigue from anemia or frequent urination caused by a large fibroid pressing on the bladder. Any decision to modify an exercise routine should be based on managing these symptoms, not on a fear that running will cause the fibroid to break down.