Muscle pain, also called myalgia, is experienced by many. The most common cause of localized muscle pain is overuse or injury of a muscle (strain). On the other hand, viral infections like influenza (the “flu”) may cause systemic muscle pain, as can taking certain medications or having a disease like fibromyalgia or hypothyroidism.1
Muscle pain can feel different—aching, cramping, stabbing, or burning—depending on what’s behind it. In the end, diagnosing the reason for your muscle pain requires a medical history, physical examination, and sometimes, blood and/or imaging tests. Rarely, a muscle biopsy is required.
Once diagnosed, your doctor will devise a treatment plan—one that will hopefully give you the relief you deserve.
Note: Muscle pain in infants and children may have different causes than in adults; this article focuses on the latter.
Due to the numerous potential causes of muscle pain, it’s easiest to divide them into two categories—those related to localized muscle pain and those that lead to systemic muscle pain.
Localized Muscle Pain
Localized muscle pain refers to pain that is focal, or centered around one muscle or group of muscles.
A muscle (or group of muscles) can become overused, injured, or inflamed as a result of strenuous exercise and/or sudden movement. For example, when pushing off suddenly to jump during a basketball game, an athlete may overstretch or tear (strain) their calf muscle.
Muscle strains often cause a sudden sharp or tearing sensation, sometimes accompanied by swelling or bruising.2
Muscle Cramp or Spasms
A muscle cramp or spasm is a contraction or tightening of a muscle that is not under your control. A classic example is a charley horse, in which your calf muscle squeezes on its own, causing a sudden, intense pain. Once the muscle relaxes (usually within seconds), your calf often feels sore.
It’s unclear what exactly causes muscles to cramp, but experts suspect a multitude of triggers, such as:
- Improper stretching
- Muscle fatigue
- Exercising in extreme heat
- Depletion of salt and electrolytes
A muscle contusion (bruise) may occur as a result of a direct blow against the muscle—for example, from falling onto a hard surface or getting hit during a sports game. This direct blow (or series of blows) essentially crushes the muscle fibers and surrounding connective tissue.
In addition to muscle pain, the skin around the painful muscle may become swollen and discolored. Moreover, a person may experience stiffness and weakness of the affected area, and in some cases, a hematoma (a collection of blood) forms around the injured muscle.2
Myofascial Pain Syndrome
Myofascial pain syndrome (MPS) is a pain disorder caused by trigger points within a muscle or group of muscles.4 These trigger points, which feel like tiny knots underneath the skin, are essentially tights bands of muscle and/or fascia (the tissue that surrounds muscles). Trigger points may be tender to the touch and refer pain to other areas of the body.
A common location for trigger points is in your upper trapezius muscles (situated at the back of your neck above each shoulder). These trapezius trigger points may cause a deep aching and/or burning headache that is felt in the back or side of the head.
Compartment syndrome is an uncommon disorder that occurs when pressure build-ups within a “compartment” or group of muscles.
There are two types of compartment syndromes:5
- With acute compartment syndrome, muscle pain develops suddenly and is extreme, constant, and often described as a deep ache or burn. Neurological symptoms like numbness or tingling may also occur with this serious condition.
- With chronic compartment syndrome, muscle pain comes on gradually during exercise. The classic case is a young runner who notes an aching, squeezing, tight, or cramping pain in the lower leg after running for a specific amount of time. Unlike acute compartment syndrome, the pain of chronic compartment syndrome goes away with rest, usually within 30 minutes.
Pyomyositis is a rare, pus-containing infection of muscle (usually from Staphylococcus aureus) that causes cramping muscle pain within a single muscle group, most commonly the thigh, calf, or buttock muscles.
As the infection progresses (approximately two weeks after the onset of the cramping pain), a fever often develops, and the muscle becomes exquisitely tender and swollen. At this time, an abscess (a collection of pus) may be visible within the muscle.
If not treated, the infection can spread to other organs, like the heart, lungs, and brain.6
Systemic Muscle Pain
Systemic muscle pain, which is felt all over your body, is often related to an infection, medication side effect, or underlying illness.
Several types of infections, especially viral, may cause muscle pain. Perhaps the most common infectious cause is influenza, commonly known as “the flu.”
Besides diffuse muscle or body aches, other potential symptoms of influenza include fever/feeling feverish, chills, headache, cough, sore throat, runny/stuffy nose, and unusual fatigue.7 Vomiting and/or diarrhea may also occur, although this is more common in children than adults.
Other infections that may cause muscle pain include:1
- Lyme disease
- Polio or post-polio syndrome
- Dengue fever
- Rocky Mountain spotted fever
- Trichinosis (roundworm infection)
- Toxoplasmosis (a disease resulting from a parasitic infection)
One common medication that may cause mild-to-moderate muscle aches and weakness as a side effect is a statin, which is used to lower cholesterol. If muscle aches do occur with a statin, they generally begin within six months of starting the drug and resolve within approximately two months (on average) of stopping the drug.8
Besides statins, other medications associated with muscle pain include:
- Bisphosphonates (used to treat osteoporosis)9
- Aromatase inhibitors10 (used to prevent breast cancer recurrence)
- Rapid withdrawal from an antidepressant
Fibromyalgia is a chronic pain disorder that causes widespread muscle pain, often described as aching, sore, stiff, burning, or throbbing.
In addition to muscle pain, people with fibromyalgia also may experience sleep problems, fatigue, headache, “crawling” sensations on their skin, morning stiffness, brain fog, and anxiety.11
Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)
Chronic fatigue syndrome, also known as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), is a disorder that causes a person to experience overwhelming fatigue that is often worsened with physical or mental activity, yet not improved with rest.
In addition to debilitating pain, many people with chronic fatigue syndrome report diffuse muscle and joint aches, as well as concentration and memory problems, sore throat, and/or feeling dizzy or lightheaded when standing up.12
The ambiguous nature of fibromyalgia and ME/CFS symptoms is, in part, why these conditions are quite difficult to diagnose.