Last updated date: 10-Mar-2024

Originally Written in English

Muscle strains Explained

    Muscle strains are one of the most common ways to get injured during exercise. They can also be one of the least serious injuries. Depending on how bad your muscle strain is, a muscle strain may be just a case of stiffness in the injury site that lasts a few days or weeks. Muscle strains are injuries to your muscles and tendons which can cause pain, bruising, swelling, and tenderness at the site of your injury. This article explains everything you need to know about muscle strains!


    What are muscles?

    Muscles are a vital component of our day-to-day life, as they help us breathe, digest food, speak, run, jump, and most importantly, they keep our hearts beating. There are two types of muscles: smooth (involuntarily controlled) and striated or skeletal (voluntary controlled) muscles. The heart is a special kind of muscle as it has the microscopical aspect and function of a striated muscle and the characteristics of a smooth muscle, as we have no control over its beating. Smooth muscles ensure the proper function of our organs, and skeletal muscles are responsible for locomotion.

    The skeletal muscles are made of muscle fibers and layers of connective tissue. About 250 muscle fibers bundle together and form an endomysium, which is considered the functional unit of the muscles, also known as the primary bundle. A lot of these primary bundles are formed, and then, they, too, bundle together and then are wrapped all around by the perimysium, thus the secondary bundle forms. Finally, the entire muscle is encircled by the epimysium. Muscles are separated from the surrounding structures by their fascia, which is a thin, tight-wrapped layer of connective tissue. Aside from protecting the muscles from their surroundings, the fascia also plays a role in binding parts of the body together.

    The muscle fiber is made of sarcomeres (the basic units of a skeletal muscle, as they gave the muscle the ability to contract and relax) which contain a big number of myofibrils; the myofibrils are made of two main myofilaments (protein filaments) called actin (the thin, bright layer) and myosin (the thick, dark layer), that are placed in a parallel manner, and a slightly secondary type of myofilament called elastic, that is made of a springy form of a protein called titin. The actin filaments bind to the lateral ends of each sarcomere (these portions are called the Z bands).

    When muscles contract, the inextensible myosin filaments, which form the A bands, remain centered as the I bands, formed by actin filaments, change their length along with the sarcomere. A sliding movement of the filaments can be observed as each sarcomere shortens due to the contraction. The sliding movements of actin and myosin filaments, when the contraction happens, generate the necessary tension within the muscle, for it to carry out the proper movement. This observation called “The sliding filament theory” lies at the basis of the mechanism of our voluntary muscle movements. The same myofilaments responsible for the physiological muscle contraction are the ones that are damaged when a muscle strain occurs.


    What are muscle strains?


    A muscle strain can appear directly into the muscle or in the muscle-tendon. The tendon is the flexible, strong cord of connective tissue that connects the muscle to the joints.

    Some muscles are prone to straining due to their insertion on two joints. These muscles, though they have a greater capacity to change their lengths and generate movement, lack resistance when it comes to withstanding excessive tension. Some examples include the hamstrings, the quadriceps, neck, and back muscles.

    A muscle strain, commonly known as a pulled muscle, regardless of its site of appearance, has one mechanism of occurrence, an excessive amount of tension placed on the muscle fibers, much more than they can cope with, this eventually leading to a tear-like injury in those said muscle fibers. The excessive tension can form either from overstretching the muscle or from forcing the muscle to contract stronger than its capacities. Alongside the tearing of the muscle, small blood vessels can be damaged as a result of the primary injury, causing local hemorrhage (bleeding) or ecchymosis (bruising, though it appears in severe cases) and pain. The pain is the result of damaged nerve endings, that run alongside the muscle, in the injured area.

    These types of injuries can be frequently encountered among sprinters, marathon runners, tennis players or any other non-contact sports athletes, as the injury is not caused directly by the trauma, as seen in blunt force trauma caused by contact sports. But muscle strains are not restricted to athletes and they can occur while doing basic activities, as long as there is a sudden increase in the duration of the activity and a greater intensity of the movement.

    Muscle strains can be classified as acute or chronic. The type of muscle strain that occurs among athletes is considered chronic, as it is a result of a repetitive movement over a long period of time. The acute type can appear from something as common as walking or improper stretching before or after a sustained physical activity like running, jumping or lifting and throwing heavy objects.


    Predisposing factors

    Besides the susceptibility of some muscle groups to strain, there are other factors that can increase the risk of occurrence of this condition. There are two categories of predisposing factors as follows:

    • The extrinsic factor is represented by cold weather as the muscles become stiffer and stiffer to try and generate heat for our bodies and therefore can easily strain during improper movements in this state.
    • The intrinsic factors can be subdivided in:
    1. Modifiable: fitness and skill levels, body composition and psychological factors;
    2. Non-modifiable: age, sex, body anatomy (defective alignment), and health (previous injuries or instability of joints).


    Symptoms of a strained muscle

    Symptoms of a strained muscle

    Considering the extension of the injury, the intensity of the clinical symptoms, and the loss of function that follows the injury, muscle strains are classified into three categories. The classification also helps physicians diagnose the condition and offer suitable treatment options in a more facile manner.

    • Grade I strain is represented by damage to only a few muscle fibers, caused either by overstretching or sudden improper movements. The strength and function of the muscle do not suffer alterations. Common symptoms for this grade are tenderness and pain at the site of the injured muscle, but it’s considered a mild pathology.
    • Grade II strain is a moderate strain and it involves a greater number of damaged muscle fibers. The symptoms are similar to the ones occurring in the grade I strain, but their intensity is greater. Besides the pain and tenderness, some mild swelling (edema) and occasional bruising can be present. A loss of strength of the affected muscle can be noticeable.
    • Grade III strain is a serious, severe type of strain that is defined by a tear that goes all the way through the muscle, breaking it into two or more separate pieces or shearing it away from its tendon. The loss of function is complete and the clinical symptoms include considerable pain, swelling, tenderness, and discoloration.

    Even though the intensity and extension of the clinical manifestations differ from one grade to another, according to the severity of the injury, the muscle strain symptoms all include pain, tenderness, and some level of swelling. 

    Of course, the symptoms can also differ based on the regions of the body where the injury initially occurs: 

    • Muscle strain in the back: increased pain while moving, cramping or spasms of the injured muscle as well as decreased range or function of the joint. Patients might experience difficulty walking or bending forward or sideways, and increased pain even when standing up straight 
    • Muscle strains in the arms or muscle strain in the legs: limited motion, muscle spasms, and weakness
    • Muscle strains in the neck: stiff neck, sharp localized pain, muscle spasms, and achy pain that can prevent or affect sleeping.

    The symptoms mentioned above qualify for an acute type of muscle strain. A chronic muscle strain tends to go unnoticed at first, at it typically has a gradual onset of pain and dysfunction. This happens due to the repetitive occurrence of the strains that cause the muscle fiber to break down but in a slow manner. The initial breakdown is healed by the body’s physiological means, but if the strains continue to appear, which is often the case, it reaches a point where the body cannot heal the damage as fast as it is provoked. This is the moment when pain appears.


    Strain vs Sprain

    As mentioned above, the strain occurs when a certain muscle is misused or overused and it can affect the muscle itself or the tendon connecting the muscle to the joint. 

    A sprain is an affection of the ligaments, bands of connective tissue that connect the bones, caused by overstretching or tearing.

    The biggest clinical difference between the two is the bruising. Even though a muscle strain bruise can occur with a moderate to severe case of the injury, the bruising is usually a sign of a sprained muscle, as it is caused by the tearing of the blood vessels that go alongside the ligaments.


    How to diagnose a muscle strain?

    diagnose a muscle strain

    A complete patient history and physical exam are usually more than enough to diagnose a strained muscle safely for a mild to moderate muscle strain (grades I and II). However, for a severe muscle strain (grade III) the healthcare professional may be able to feel a tear or gap beneath the skin, during the physical exam. This alone is not enough for an accurate diagnosis so an MRI is needed to clinically assess if the rupture of injured muscle is complete or not. The MRI is useful to diagnose any secondary damage, like a hematoma, a collection of blood caused by a ruptured blood vessel, that is collected under the surface of the skin.

    The X-rays are a useful paraclinical tool for a proper differential diagnosis, as they can show fractures or dislocations that can mimic a strained muscle.


    The process of muscle regeneration

    There are three physiological phases of the regeneration process that occur when a muscle is injured, either by a strain or contusion (destruction of muscular tissues and blood vessels caused by direct trauma):

    • Destruction: the initial phase that occurs when the injury happens and lasts throughout the first days after the trauma; the muscle tissue has an adaptive mechanism that prevents the injury site from enlargement, by “sealing off” the damaged site to ensure the phases of the regeneration process only occur in this specific site alone;
    • Repair: during the second phase, a cell called a macrophage is introduced into the damaged area, its role is “to clean away” the dead tissue and dry blood caused by the injury. Once the macrophage phase is complete, another cell, a satellite cell, is released onto the site. The satellite cells have a very important role, they transform into myoblast cells; the newly formed myoblast cells merge to create a new muscle fiber. The peak of this phase usually occurs about two weeks after the trauma;
    • Remodeling: the last phase overlaps considerably with the repair phase, so it’s hard to mention when one ends and the other begins. During this phase, the regenerating muscle fibers and connective tissue continue to mature and are being oriented into the final scar tissue. The biggest concern of this phase is the manner in which the scar tissue is oriented, because as the tissue reapers itself, the physiological straight-oriented lines of the muscle tissue become randomly oriented.


    How to cure a muscle strain?

    Muscle strain chart

    For the acute phase of a strained muscle, the first-line of treatment is composed of five steps, commonly known as P.R.I.C.E:

    • Protection: refers to covering the injured area with a soft padding, to keep the impact with the surrounding objects to a minimum;
    • Rest: rest and muscle relaxation are necessary to accelerate healing; with proper healing, the risk of re-injury is reduced considerably;
    • Ice: applying ice to the injured area, but not for more than 20 minutes at a time, is necessary because it causes vasoconstriction, which reduces the blood flow to the damaged site of injury;
    • Compression: consists of wrapping the strained muscular site with a soft bandage, which significantly reduces the progression of diapedesis (the passage of blood cells through the intact walls of the capillaries) and promotes the drainage of the lymphatic vessels, also decreasing the inflammation signs;
    • Elevation: represents keeping the strained area as close to the level of the heart as possible; this promotes venous blood return to the systemic circulation.

    To ensure the efficiency of the P.R.I.C.E. treatment, adjunctive medication therapy like NSAIDs (non-steroidal anti-inflammatory drugs) is frequently used, especially for moderate to severe cases. Some commonly prescribed NSAIDs are ibuprofen and naproxen.Their main purpose, as the name indicates, is to reduce the immediate inflammation caused by the injury. The dosage of NSAIDs should be decided after consulting a physician, as it should meet the specific needs of the patient.

    New treatments like platelet-rich-plasma injections (PRP injections) are used to accelerate the recovery of muscle strains, that are considered non-surgical. By using biological factors, studies have shown that the occurrence of the physiological phases involved in the muscle regeneration process are favored to appear faster.

    After the first-line treatment represented by P.R.I.C.E, which should last about a week, mobilization must begin. It is recommended that the mobilization process starts as soon as possible, the only limitation being the patient’s pain threshold. The mobilization increases gradually within those limits of pain. It is shown that mobilization improves the regeneration of injured striated muscles. Progressive functional physical therapy is always an option and should be used when needed.

    After 2-3 weeks have passed since the injury, normal tension must be applied to the injured muscle for the proper remodeling, anatomical and functional.

    The treatment should also be adapted accordingly to the physiological phase of the regenerative process, in which the patient presents themselves when asking for a consult.


    Treatment for the destruction phase:

    • Immobilization for 3 to 7 days
    • P.R.I.C.E treatment

    Treatment for the repair phase:

    • Transitioning from immobilization to mobilization
    • Physical therapy

    Treatment for the remodeling phase:

    • Manual therapy
    • Specialized treatment techniques

    The only treatment option for chronic muscle strains is physiotherapy, as it helps to break the scarring tissue formed at the site of the injury and increases elasticity, both needed to realign the muscle fiber from a random manner to straight parallel lines.


    Recovery time

    A muscle strain recovery time ranges accordingly to the severity of the injury as follows:

    • Mild muscle strain, which only involves muscle tissue, takes about 3 to 6 weeks to heal.
    • Moderate to severe muscle strains that involve mostly the muscle tissue, take about 8 to 12 weeks to heal.
    • Tendon-involving muscle strain takes more than four months to heal properly.



    Complications muscle strain

    Different types of complications can occur due to a muscle strain, they can be categorized according to their onset, they can be caused either by the injury itself, by a misdiagnosis, or by a misconducted treatment plan.

    Early-onset complications occur when a cased is misdiagnosed and no MRI imagining is performed in order to assess the presence of hematomas. A hematoma within the muscle that does not receive adequate treatment can cause an acute compartment syndrome (increased tissue pressure in an inextensible compartment due to the presence of the hematoma). The hematoma could also lead to the compression of the popliteal or gastrocnemius veins (if the injury interests the posterior muscles of the calves).

    Intermediate onset complications can be caused by inadequate use of P.R.I.C.E treatment, as patients often do not let the injured muscle rest and return to their regular activities too early thus early recurrences are often present. Also, increased age and decreased mobility are associated with recurrences.

    Delayed onset complications are represented by a decrease in muscle elasticity caused by permanent scar tissue and adhesions.

    The complication caused by treatment consists of an early mobilization that is too rough and determines a re-rupture of the muscle, as the newly formed muscle fibers do not yet have the necessary strength to sustain movement.



    A case of re-injury of a strained muscle should always be avoided and there are several ways and methods to perform in order to prevent re-injury or recurrence from happening, like:

    • Allowing the injury to properly heal, by taking a break from the physical activities that involve the affected muscle, for the recommended amount of time by the doctor;
    • Forming a daily habit of stretching all muscles;
    • Performing physical activities that strengthen the muscles;
    • Warming up and cooling down after every intense physical activity;
    • Eating foods with high levels of potassium (avocados, bananas) before exercise to prevent muscle fatigue;
    • Hydrating properly during physical activities.



    A muscle strain is a contraction-induced injury caused by extensive mechanical stress, that can appear either from overusing the muscle or from misusing the muscle. Some muscles are prone to straining due to:

    • Their insertion on two different joints;
    • The way they contract: eccentric contractions may change the tension inside the muscle and cause an overload injury (examples of eccentric contractions: running, sprinting);
    • The high-speed contractions they can develop, such muscles are the hamstrings, gastrocnemius, quadriceps, hip flexors, hip adductors, Erector Spinae, deltoid, and neck muscles.

    Usually, muscle strain treatment plans are easily conducted and are manageable for the patient, as they are mostly based on letting the injured area rest. The mild muscle strains can be treated at home, using the P.R.I.C.E treatment (protection, rest, ice, compression, and elevation) and the recovery time is short, about five weeks on average. But the severe type of strains can cause serious repercussions and need qualified medical assistance in order to properly heal and also require a longer recovery time. For a proper assessment of the injury’s severity and an adequate treatment plan, a medical doctor should always be consulted.