Muscle pain, or myalgia, is a common symptom of many conditions and disorders. The most common cause for myalgia is either overuse or over-stretching of a muscle or group of muscles. Muscle pain arising without a history of trauma or overuse of the muscles is often caused by viral infections. Persistent muscle pain, associated with weakness, may be a symptom of a metabolic myopathy – a defect of the muscle metabolism, leading to impaired muscle function.

The most common causes of myalgia by injury are sprains and strains (Pic. 1). An injury happens when the muscle is stretched too far and the pain can be felt at the same moment or in some cases latter during the cooling down phase after the exercise and sometimes the pain radiates to the upper arm or neck. It also usually presents with swelling and redness of the affected muscle and fever. Acute muscular strain injuries are frequently found in sports, at both amateur and competitive level. Muscular injuries can occur anywhere on our whole body. The treatment methods available to us today are of such a wide variety that the athlete can to return to physical activity as soon as possible (in most of the cases) without any permanent damage or secondary reactions. 

Muscle pain without previous injury is commonly seen in viral infections, such as the influenza, measles or mumps. Many viruses cause a condition that is very similar to the onset of influenza, and is therefore called influenza-like, or flu-like illness. Symptoms commonly include fever, shivering, chills, malaise, dry cough, loss of appetite, body aches due to muscle pain and joint pain, and nausea, typically in connection with a sudden onset of illness. In most cases, the symptoms are caused by cytokines (signaling molecules of the immune system) released by immune system activation and are thus relatively non-specific.

Muscle pain may be associated with many conditions, including:


Mumps is a viral disease caused by the mumps virus. Like many other viruses, the mumps virus is transmitted by respiratory droplets or direct contact with an infected person. Mumps is highly contagious and spreads rapidly among people living in close quarters. Initial signs and symptoms often include fever, muscle pain, headache, and feeling tired. This is then usually followed by painful swelling of one or both parotid salivary glands (Pic. 2). Symptoms typically occur 16 to 18 days after exposure and resolve after seven to ten days. One of the possible complications is painful testicular inflammation, which develops in 15–40 percent of men who have completed puberty and contract the mumps virus. This testicular inflammation is generally one-sided (both testicles are swollen in 15–30 percent of mumps orchitis cases) and typically occurs about 10 days after the parotid gland inflamed. Testicular swelling has been documented as late as six weeks after parotid gland swelling. Orchitis can be unilateral (one sided) or bilateral (both sided). Bilateral orchitis leads to oligospermia (low sperm count) and testicular atrophy (any reduction in testicular size). Following mumps orchitis, sperm morphology (specific structural features) deterioration is a long-lasting effect. Spermiogenesis (development of sperm from germ cells) was greatly disrupted in half of the patients. In many patients whose testes were not atrophied, poor fertility was found persistently. According to the observations, sperm morphology was the most influenced, of the characteristics that were studied, and sperm count might be the least affected. Women may develop ovarian swelling but this does not increase the risk of infertility.

Autoimmune disorders

Autoimmune diseases are those in which the body is attacked by its own specific adaptive immune response. In normal, healthy states, the immune system induces tolerance, which is a lack of an anti-self immune response. However, with autoimmunity, there is a loss of immune tolerance. One or more organs or tissues are then damaged or destroyed by the body´s own immune system. Myalgia is a common symptom in systemic autoimmune disorders (affecting multiple organs or organ systems), such as systemic lupus erythematodes (SLE), rheumatoid arthritis, or multiple sclerosis. SLE is an example of an autoimmune disease that can present with myalgia and myositis (muscle inflammation). Generalised muscle aches are amongst the most common symptoms (Pic. 3). Lupus erythematosus itself usually does not affect fertility. However, the disease may influence both male and female fertility by various other mechanisms, such as older age of patients compared to healthy individuals, lowered fitness and drugs used to treat lupus, which can damage the reproductive organs.


Mumps ―sourced from Wikipedia licensed under CC BY- SA 3.0
Mumps ―sourced from licensed under CC BY- SA 4.0
Diagnostic Imaging in Muscle Injury ―by Manara et al. licensed under CC BY 3.0
Overview of Different Location of Muscle Strain ―by Arroyo, Francisco licensed under CC BY 3.0
Myalgia ―sourced from Wikidoc licensed under CC BY-SA 3.0
Influenza-like illness ―sourced from Wikipedia licensed under CC BY-SA 3.0
Myalgia ―sourced from Wikipedia licensed under CC BY-SA 3.0
Microbiology ―sourced from OpenStax College licensed under CC BY 4.0
Muscle strain ―by Daniel.Cardenas licensed under CC BY 3.0
Mumps ―by CDC's Public Health Image Library licensed under CC0 1.0
Symptoms of SLE ―by Mikael Häggström licensed under CC0 1.0
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