In the common presentation of acute low back pain, pain develops after movements that involve lifting, twisting, or forward-bending. The symptoms may start soon after the movements or upon waking up the following morning. The description of the symptoms may range from tenderness at a particular point to diffuse pain. It may or may not worsen with certain movements, such as raising a leg, or positions, such as sitting or standing. Pain radiating down the legs (known as sciatica) may be present. The first experience of acute low back pain is typically between the ages of 20 and 40. This is often a person's first reason to see a medical professional as an adult. Recurrent episodes occur in more than half of people with the repeated episodes being generally more painful than the first.

Other problems may occur along with low back pain. Chronic low back pain is associated with sleep problems, including a greater amount of time needed to fall asleep, disturbances during sleep, a shorter duration of sleep, and less satisfaction with sleep. In addition, a majority of those with chronic low back pain show symptoms of depression or anxiety.

Back pain may be classified by various methods to aid its diagnosis and management. The duration of back pain is considered in three categories, following the expected pattern of healing of connective tissue. Acute pain lasts up to 12 weeks, subacute pain refers to the second half of the acute period (6 to 12 weeks), and chronic pain is pain which persists beyond 12 weeks.

Weakness or asthenia is a symptom of a number of different conditions. The causes are many and can be divided into conditions that have true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, including muscular dystrophy and inflammatory myopathy. It occurs in neuromuscular junction disorders, such as myasthenia gravis.

Asthenia (Greek: "ἀσθένεια", lit "lack of strength" but also "disease") is a medical term referring to a condition in which the body lacks or has lost strength either as a whole or in any of its parts. It denotes symptoms of physical weakness and loss of strength. General asthenia occurs in many chronic wasting diseases (such as tuberculosis and cancer), sleep disorders or chronic disorders of the heart, lungs or kidneys, and is probably most marked in diseases of the adrenal gland. Asthenia may be limited to certain organs or systems of organs, as in asthenopia, characterized by ready fatiguability. Asthenia is also a side effect of some medications and treatments, such as Ritonavir (a protease inhibitor used in HIV treatment), vaccines such as the HPV vaccine Gardasil and fentanyl patches (an opioid used to treat pain).

Differentiating psychogenic (perceived) asthenia and true asthenia from myasthenia is often difficult, and in time apparent psychogenic asthenia accompanying many chronic disorders is seen to progress into a primary weakness.

Myasthenia (my- from Greek μυο meaning "muscle" + -asthenia ἀσθένεια meaning "weakness"), or simply muscle weakness, is a lack of muscle strength. The causes are many and can be divided into conditions that have either true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, including muscular dystrophy and inflammatory myopathy. It occurs in neuromuscular diseases, such as myasthenia gravis.

Back pain is pain in any region of the back. It is divided into neck pain (cervical), middle back pain (thoracic), lower back pain (lumbar) or coccydynia (tailbone or sacral pain) based on the segment affected. The lumbar area is the most common area for pain, as it supports most of the weight in the upper body. Episodes of back pain may be acute, sub-acute, or chronic depending on the duration. The pain may be characterized as a dull ache, shooting or piercing pain, or a burning sensation. Discomfort can radiate into the arms and hands as well as the legs or feet, and may include numbness, or weakness in the legs and arms.

Back pain can originate from the muscles, nerves, bones, joints or other structures in the spine. Internal structures such as the gallbladder, pancreas, aorta, and kidneys may also cause referred pain in the back.

Back pain is common, with about nine out of ten adults experiencing it at some point in their life, and five out of ten working adults having it every year. Some estimate up to 95% of Americans will experience back pain at some point in their lifetime. It is the most common cause of chronic pain, and is a major contributor of missed work and disability. However, it is rare for back pain to be permanently disabling. In most cases of herniated disks and stenosis, rest, injections or surgery have similar general pain resolution outcomes on average after one year. In the United States, acute low back pain is the fifth most common reason for physician visits and causes 40% of missed days off work. Additionally, it is the single leading cause of disability worldwide.

There are a number of ways to classify low back pain with no consensus that any one method is best. There are three general types of low back pain by cause: mechanical back pain (including nonspecific musculoskeletal strains, herniated discs, compressed nerve roots, degenerative discs or joint disease, and broken vertebra), non-mechanical back pain (tumors, inflammatory conditions such as spondyloarthritis, and infections), and referred pain from internal organs (gallbladder disease, kidney stones, kidney infections, and aortic aneurysm, among others). Mechanical or musculoskeletal problems underlie most cases (around 90% or more), and of those, most (around 75%) do not have a specific cause identified, but are thought to be due to muscle strain or injury to ligaments. Rarely, complaints of low back pain result from systemic or psychological problems, such as fibromyalgia and somatoform disorders.

Low back pain may be classified based on the signs and symptoms. Diffuse pain that does not change in response to particular movements, and is localized to the lower back without radiating beyond the buttocks, is classified as "nonspecific", the most common classification. Pain that radiates down the leg below the knee, is located on one side (in the case of disc herniation), or is on both sides (in spinal stenosis), and changes in severity in response to certain positions or maneuvers is "radicular", making up 7% of cases. Pain that is accompanied by red flags such as trauma, fever, a history of cancer or significant muscle weakness may indicate a more serious underlying problem and is classified as "needing urgent or specialized attention".

The symptoms can also be classified by duration as acute, sub-chronic (also known as sub-acute), or chronic. The specific duration required to meet each of these is not universally agreed upon, but generally pain lasting less than six weeks is classified as "acute", pain lasting six to twelve weeks is "sub-chronic", and more than twelve weeks is "chronic". Management and prognosis may change based on the duration of symptoms.

Patients with trochleitis typically experience a dull fluctuating aching over the trochlear region developing over a few days. Some may also feel occasional sharp pains punctuating the ache. In patients with migraines, trochleitis may occur simultaneously with headache. Presentation is usually unilateral with palpable swelling over the affected area supranasal to the eye. The trochlear region is extremely tender to touch. Pain is exacerbated by eye movements looking down and inwards, and especially in supraduction (looking up) and looking outwards, which stretches the superior oblique muscle tendon. Notably, there is no restriction of extraocular movements, no diplopia, and often no apparent ocular signs such as proptosis. However, occasionally mild ptosis is found. The absence of generalized signs of orbital involvement is helpful in eliminating other more common causes of periorbital pain.

Muscle weakness or myasthenia (my- from Greek μυο meaning "muscle" + -asthenia ἀσθένεια meaning "weakness") is a lack of muscle strength. The causes are many and can be divided into conditions that have either true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, including muscular dystrophy and inflammatory myopathy. It occurs in neuromuscular junction disorders, such as myasthenia gravis. Muscle weakness can also be caused by low levels of potassium and other electrolytes within muscle cells. It can be temporary or long-lasting (from seconds or minutes to months or years).

Muscle weakness can be classified as either "true" or "perceived" based on its cause.

- True muscle weakness (or neuromuscular weakness) describes a condition where the force exerted by the muscles is less than would be expected, for example muscular dystrophy.

- Perceived muscle weakness (or non-neuromuscular weakness) describes a condition where a person feels more effort than normal is required to exert a given amount of force but actual muscle strength is normal, for example chronic fatigue syndrome.

In some conditions, such as myasthenia gravis, muscle strength is normal when resting, but "true" weakness occurs after the muscle has been subjected to exercise. This is also true for some cases of chronic fatigue syndrome, where objective post-exertion muscle weakness with delayed recovery time has been measured and is a feature of some of the published definitions.

Trochleitis is inflammation of the superior oblique tendon trochlea apparatus characterized by localized swelling, tenderness, and severe pain. This condition is an uncommon but treatable cause of periorbital pain. The trochlea is a ring-like apparatus of cartilage through which passes the tendon of the superior oblique muscle. It is located in the superior nasal orbit and functions as a pulley for the superior oblique muscle. Inflammation of the trochlear region leads to a painful syndrome with swelling and exquisite point tenderness in the upper medial rim of the orbit. A vicious cycle may ensue such that inflammation causes swelling and fraying of the tendon which then increases the friction of passing through the trochlea which in turn adds to the inflammation. Trochleitis has also been associated with triggering or worsening of migraine attacks in patients with pre-existing migraines (Yanguela, 2002).

Patients with acquired non-inflammatory myopathy typically experience weakness, cramping, stiffness, and tetany, most commonly in skeletal muscle surrounding the limbs and upper shoulder girdle.

The most commonly reported symptoms are:

- Muscle fatigue

- Pain

- Muscle spasms and cramps

- Tingling

- Numbness

- Tetany

- Loss of coordination and balance

- Lack of fine and gross motor control

- Muscular wasting and atrophy

Macrophagic Myofasciitis, or MMF, is a rare muscle disease identified in 1993. The disease is characterized by microscopic lesions found in muscle biopsies that show infiltration of muscle tissue by PAS-positive macrophages.

Specific causes of MMF are unknown. Intramuscular injections of aluminium-containing vaccines have been implicated. Many of those affected with the disease had previously been treated for malaria with chloroquine or hydroxychloroquine.

Clinical symptoms include muscle pain, joint pain, muscle weakness, fatigue, fever, and muscle tenderness. A diagnosis can only be identified with an open muscle biopsy of the vaccinated muscle.

Studies at the University of Paris have shown that MMF lesions result when the aluminum hydroxide adjuvant from a vaccine remains embedded in the tissue and causes a steady immune reaction.

As of 2009 and with few exceptions, MMF had only been observed in France.

Odynophagia may have environmental or behavioral causes, such as:

- Very hot or cold food and drinks

- Taking certain medications

- Using drugs, tobacco, or alcohol

- Trauma or injury to the mouth, throat, or tongue

Odynophagia (; from "-" "pain" and "" "to eat") is pain when swallowing. The pain may be felt in the mouth or throat and can occur with or without difficulty swallowing. The pain may be described as an ache, burning sensation, or occasionally a stabbing pain that radiates to the back. Odynophagia often results in inadvertent weight loss.

Acquired noninflammatory myopathy can be caused by a variety of factors including metabolic abnormalities, drugs, nutritional deficiency, trauma, and upstream abnormalities resulting in decreased function. Two of the most common causes of ANIM are hyperthyroidism and excessive steroid use, while many drugs used to treat rheumatism are known to be inducing agents. Most cases of ANIM can be linked to drugs or dietary abnormalities.

Classic symptoms of muscle imbalances are usually pain associated with the affected joint. Symptoms can vary depending on what stage their muscular imbalance is, functional or pathological, but commonly exhibit small tissue damage or lesions accompanied by a change in muscle movement patterns. Symptoms may occur after injury or surgery, where the recuperation of the joint affected is left untreated causing either tension or restriction to flexibility and strength of the prime movers.

Scoliosis, is a medical condition where a person's spine has several irregular curves that are located between the neck and the pelvis. Symptoms of scoliosis in mild cases usually exhibit abnormal posture, back pain, tingling or numbness in the legs and in worse cases can exhibit breathing problems, fatigue, permanent deformities and in rare cases heart problems.

Muscle atrophy is defined as a decrease in the mass of the muscle; it can be a partial or complete wasting away of muscle, and is most commonly experienced when persons suffer temporary disabling circumstances such as being restricted in movement and/or confined to bed as when hospitalized. When a muscle atrophies, this leads to muscle weakness, since the ability to exert force is related to mass. Modern medicine's understanding of the quick onset of muscle atrophy is a major factor behind the practice of getting hospitalized patients out of bed and moving about as active as possible as soon as is feasible, despite sutures, wounds, broken bones and pain.

Muscle atrophy results from a co-morbidity of several common diseases, including cancer, AIDS, congestive heart failure, COPD (chronic obstructive pulmonary disease), renal failure, and severe burns; patients who have "cachexia" in these disease settings have a poor prognosis. Moreover, starvation eventually leads to muscle atrophy.

Disuse of the muscles, such as when muscle tissue is immobilized for even a few days of unuse – when the patient has a primary injury such as an immobilized broken bone (set in a cast or immobilized in traction), for example – will also lead rapidly to disuse atrophy. Minimizing such occurrences as soon as possible is a primary mission of occupational and physical therapists employed within hospitals working in co-ordination with orthopedic surgeons.

Neurogenic atrophy, which has a similar effect, is muscle atrophy resulting from damage to the nerve which stimulates the muscle, causing a shriveling around otherwise healthy limbs. Also, time in a circa zero g environment without exercise will lead to atrophy. This is partially due to the smaller amount of exertion needed to move about, and the fact that muscles are not used to maintain posture. In a similar effect, patients with a broken leg joint undergoing as little as three weeks of traction can lose enough back and buttocks muscle mass and strength as to have difficulty sitting without assistance, and experience pain, stress and burning even after a very short ten-minute exposure, when such positioning is contrived during recovery.

Orchialgia is long-term pain of the testes. It is considered chronic if it has persisted for more than 3 months. Orchialgia may be caused by injury, infection, surgery, cancer or testicular torsion and is a possible complication after vasectomy. IgG4-related disease is a more recently identified cause of chronic orchialgia.

One author describes the syndromes of chronic testicular pain thus:"The complaint is of a squeezing deep ache in the testis like the day after you got kicked there, often bilateral or alternating from one side to the other, intermittent, and, most commonly, associated with lower back pain. Sometimes it feels like the testicle is pinched in the crotch of the underwear but trouser readjustment does not help. There may also be pain in the inguinal area but no nausea or other symptoms. Back pain may be concurrent or absent and some patients have a long history of low back pain. Onset of pain is commonly related to activity that would stress the low back such as lifting heavy objects. Other stresses that might cause low back pain are imaginative coital positions, jogging, sitting hunched over a computer, long car driving, or other such positions of unsupported seating posture that flattens the normal lumbar lordosis curve."

A number of terms are used to describe critical illness polyneuropathy, partially because there is often neuropathy and myopathy in the same person, and nerve and muscle degeneration are difficult to distinguish from each other in this condition. Terms used for the condition include: critical illness polyneuromyopathy, critical illness neuromyopathy, and critical illness myopathy and neuropathy (CRIMYNE). Bolton's neuropathy is an older term, which is no longer used.

People with CIP/CIM have diffuse, symmetric, flaccid muscle weakness. CIP/CIM typically develops in the setting of a critical illness and immobilization, so patients with CIP/CIM are often receiving treatment in the intensive care unit (ICU).

Weakness (motor deficits) occurs in generalized fashion, rather than beginning in one region of the body and spreading. Limb and respiratory (diaphragm) muscles are especially affected. The muscles of the face are usually spared, but in rare cases, the eye muscles may be weakened, leading to ophthalmoplegia.

Respiratory difficulties can be caused by atrophy of the muscles between the ribs (intercostals), atrophy of the diaphragm muscle, and degeneration of the nerve that stimulates the diaphragm (phrenic nerve). This can prolong the time the wean a person off of a breathing machine (mechanical ventilation) by as much as 7 – 13 days.

Deep tendon reflexes may be lost or diminished, and there may be bilateral symmetric flaccid paralysis of the arms and legs. The nervous system manifestations are typically limited to peripheral nerves, as the central nervous system is usually unaffected.

Muscular atrophy decreases qualities of life as the sufferer becomes unable to perform certain tasks or worsen the risks of accidents while performing those (like walking). Muscular atrophy increases the risks of falling in conditions such as inclusion body myositis (IBM) . Muscular atrophy affects a high number of the elderly.

The symptoms of rhabdomyolysis depend on its severity and whether kidney failure develops. Milder forms may not cause any muscle symptoms, and the diagnosis is based on abnormal blood tests in the context of other problems. More severe rhabdomyolysis is characterized by muscle pain, tenderness, weakness and swelling of the affected muscles. If the swelling is very rapid, as may happen after someone is released from under a collapsed building, the movement of fluid from the bloodstream into damaged muscle may cause low blood pressure and shock. Other symptoms are nonspecific and result either from the consequences of muscle tissue breakdown or from the condition that originally led to the muscle breakdown. Release of the components of muscle tissue into the bloodstream causes electrolyte disturbances, which can lead to nausea, vomiting, confusion, coma or abnormal heart rate and rhythm. The urine may be dark, often described as "tea-colored", due to the presence of myoglobin. Damage to the kidneys may give rise to decreased or absent urine production, usually 12 to 24 hours after the initial muscle damage.

Swelling of damaged muscle occasionally leads to compartment syndrome—compression of surrounding tissues, such as nerves and blood vessels, in the same fascial compartment—leading to the loss of blood supply and damage or loss of function in the part(s) of the body supplied by these structures. Symptoms of this complication include pain or reduced sensation in the affected limb. A second recognized complication is disseminated intravascular coagulation (DIC), a severe disruption in blood clotting that may lead to uncontrollable bleeding.

Hypokalemic periodic paralysis (hypoKPP) is a rare, autosomal dominant channelopathy characterized by muscle weakness or paralysis when there is a fall in potassium levels in the blood. In individuals with this mutation, attacks often begin in adolescence and most commonly occur on awakening or after sleep or rest following strenuous exercise (attacks during exercise are rare), high carbohydrate meals, meals with high sodium content, sudden changes in temperature, and even excitement, noise, flashing lights and cold temperatures. Weakness may be mild and limited to certain muscle groups, or more severe full-body paralysis. During an attack reflexes may be decreased or absent. Attacks may last for a few hours or persist for several days. Recovery is usually sudden when it occurs, due to release of potassium from swollen muscles as they recover. Some patients may fall into an abortive attack or develop chronic muscle weakness later in life.

Some people only develop symptoms of periodic paralysis due to hyperthyroidism (overactive thyroid). This entity is distinguished with thyroid function tests, and the diagnosis is instead called thyrotoxic periodic paralysis.

The speed of the progression of JDMS is highly variable. Nearly all JDM patients have some skin involvement. The JDMS rash usually occurs as the initial symptom. Sometimes it is so slight as not to be recognized for what it is until muscle symptoms appear. Sometimes muscle symptoms never appear at all or occur very gradually over the course of months, and sometimes going from normal strength to being unable to walk within days. Usually, muscle symptoms appear weeks to months after the onset of the rash.