FMS most commonly stands for fibromyalgia syndrome, a chronic condition that causes widespread pain, fatigue, and heightened sensitivity throughout the body. It affects roughly 2% to 3% of the population, and women are twice as likely as men to be diagnosed. In sports medicine, FMS can also refer to the Functional Movement Screen, a fitness assessment tool, but the vast majority of people searching this term are looking for information about fibromyalgia.
How Fibromyalgia Affects the Body
Fibromyalgia is fundamentally a problem with how the nervous system processes pain signals. In a healthy nervous system, pain signals travel from an injury site to the brain, which interprets them proportionally. In fibromyalgia, the central nervous system amplifies those signals, a process called central sensitization. The result is that stimuli which wouldn’t normally hurt, like light pressure on the skin or a firm handshake, can register as genuinely painful.
This amplification happens because of imbalances in brain chemicals that regulate pain. Levels of excitatory neurotransmitters (the ones that ramp up nerve signaling) rise, while the body’s natural pain-dampening systems don’t keep pace. People with fibromyalgia develop what researchers call an expanded pain receptive field, meaning more areas of the body become sensitive. Two hallmark features follow from this: hyperalgesia, where mildly painful things hurt far more than they should, and allodynia, where things that aren’t painful at all begin to cause pain.
The condition also disrupts the hormonal systems that regulate sleep, stress, and mood. Alterations in cortisol, growth hormone, and serotonin all play a role, which explains why fibromyalgia is never just about pain. It typically shows up in young or middle-aged adults as a package of symptoms: persistent widespread pain, stiffness, deep fatigue, unrefreshing sleep, and cognitive difficulties.
The Full Range of Symptoms
Widespread pain is the defining symptom, but fibromyalgia reaches well beyond that. Most people experience significant fatigue that doesn’t improve with rest, along with stiffness that’s often worst in the morning. Sleep is disrupted at a structural level: studies using brain wave monitoring show that people with fibromyalgia have abnormal sleep architecture. Alpha brain waves, which indicate light wakefulness, intrude into the deep sleep stages where the body normally repairs itself. Deep sleep and REM sleep are both reduced, and awakenings are more frequent. The result is sleep that feels shallow and unrestorative no matter how many hours you spend in bed.
Cognitive dysfunction, widely known as “fibro fog,” is one of the most frustrating symptoms. It involves memory impairment, reduced mental clarity, and difficulty sustaining attention and focus. Research has found that fibromyalgia produces measurable deficits in learning, memory, attention, and processing speed, with smaller but still meaningful impacts on executive function and working memory. For many people, fibro fog is more disabling than the pain itself because it interferes with work, conversation, and daily decision-making.
Anxiety and depression frequently accompany fibromyalgia as well, though they aren’t simply a reaction to living with chronic pain. The same neurotransmitter imbalances driving the pain amplification also affect mood regulation. Bowel disturbances, headaches, and jaw pain from temporomandibular joint (TMJ) dysfunction are also common. Irritable bowel syndrome overlaps so frequently with fibromyalgia that some researchers believe they share underlying mechanisms.
How Fibromyalgia Is Diagnosed
There’s no blood test or imaging scan that can confirm fibromyalgia. Diagnosis relies on clinical criteria developed by the American College of Rheumatology. The current guidelines require two things to be true: widespread symptoms must have persisted for at least three months, and those symptoms must not be better explained by another condition.
Doctors use two scoring tools together. The Widespread Pain Index tracks how many body regions are painful (out of 19 possible areas), while the Symptom Severity Scale rates fatigue, unrefreshing sleep, and cognitive problems. A diagnosis is made when the pain index reaches 7 or higher with a symptom severity score of at least 5, or when the pain index is between 4 and 6 with a symptom severity score of 9 or higher. The pain must also be generalized, affecting at least four of five body regions. Because many conditions can mimic fibromyalgia, including thyroid disorders, autoimmune diseases, and vitamin deficiencies, the diagnostic process often involves ruling those out first.
Treatment and Symptom Management
Fibromyalgia treatment works best as a combination of medication and lifestyle strategies. No single drug eliminates the condition, but certain medications can reduce pain intensity and improve sleep. Three medications have been specifically approved for fibromyalgia, including duloxetine (Cymbalta), which works by increasing the availability of serotonin and norepinephrine, two brain chemicals involved in pain suppression and mood. Not everyone responds to the same medication, so finding the right fit often takes some trial and adjustment.
Beyond medication, aerobic exercise is one of the most consistently effective tools for reducing fibromyalgia pain. The optimal approach, based on a systematic review of the available evidence, is exercising two to three times per week for 25 to 40 minutes per session, totaling more than 100 minutes weekly. The specific type of exercise matters less than doing it consistently. Walking, swimming, pool-based exercise, and stationary cycling all produce benefits. Choosing something you actually enjoy and can access easily is the strongest predictor of sticking with it long term.
This can feel counterintuitive. When your body hurts and you’re exhausted, exercise is the last thing that sounds appealing. But regular aerobic activity appears to recalibrate the pain-processing system over time, gradually raising the threshold at which stimuli register as painful. Starting slowly and building up is key, since pushing too hard too fast can trigger a symptom flare.
Conditions That Overlap With Fibromyalgia
Fibromyalgia rarely travels alone. The most common conditions that co-occur with it include irritable bowel syndrome, chronic headaches, TMJ disorders, anxiety, and depression. These overlapping conditions can make diagnosis more complicated and mean that treatment plans often need to address several problems at once. If you’ve been diagnosed with one of these conditions and also experience widespread pain and fatigue, it’s worth discussing fibromyalgia with your doctor.
FMS as the Functional Movement Screen
In sports and fitness settings, FMS refers to the Functional Movement Screen, a completely different concept. This is a screening system made up of seven movement tests that assess basic patterns like squatting, stepping, and reaching. Each test challenges your balance of mobility and stability, and the goal is to identify compensatory movement patterns, meaning ways your body has learned to work around a weakness or imbalance. The screen looks for right-to-left asymmetries and problems with how force transfers through the body during movement. It’s used by physical therapists, athletic trainers, and coaches as a tool to flag injury risk before it becomes a problem.