Calf Strain

'Original Editors ' Kim De Maeght, Bettina Vansintjan, Maite Van Roozendael and Lenka Pé


Definition/Description[edit | edit source]

Calf strain is a common muscle injury. It is a tear of the muscle fibres of the muscles at the back of the lower leg. Strains are the result of excessive stretching or stretching while the muscle is being activated. Tendons are an important part of the muscle which means strains may also involve causing damage to tendons. Strains may be referred to as a “pulled muscle”. 

Clinically Relevant Anatomy[edit | edit source]

The calf muscle, on the back of the lower leg, is composed of three muscles: the gastrocnemius, the soleus and the plantaris, which together constitute the triceps surae. These muscles come together as the achilles tendon and all three muscles insert into the calcaneus.

Gastrocnemius is part of the posterior compartment of the leg and comprises of two parts, the medial head and the lateral head. The medial head arises from the medial condyle of the femur and the lateral head originates from the lateral condyle of the femur. [1] The gastrocnemius provides primarily plantar flexion and flexion at knee joint. [2] Gastrocnemius is innervated by the tibial nerve, a branch of the sciatic nerve, passing through the popliteal fossa where the nerve gives off a branch to the gastrocnemius. 

Soleus is located beneath the gastrocnemius muscle in the superficial posterior compartment of the lower leg. The muscle originates from the upper 1/3 of the posterior aspect of the tibia, from the back of the head of the fibula and the upper part of the posterior surface of the fibular shaft and the fibrous arch that lies between the tibia and the fibula. [3] Its main function is plantar flexion of the ankle and stabilising the tibia on the calcaneus limiting forward sway. [2] The soleus is innervated by the tibial nerve, which passes behind the muscle through the fibrous arch of the soleus. 

Plantaris is located in the posterosuperficial compartment of the calf. The muscle originates from the lateral supracondylar line of the femur (superior and medial to the lateral head of gastrocnemius) and from the oblique popliteal ligament. It is a long, small muscle with a long thin tendon. The plantaris is also innervated by the tibial nerve. Functionally, plantaris is not a major contributor and acts with gastrocnemius, as both a flexor of the knee and a plantarflexor of the ankle. [4]

Epidemiology/Etiology[edit | edit source]

Muscle strains most commonly occur in bi-articular muscles such as the hamstrings, rectus femoris and gastrocnemius. During sporting activities such as sprinting, these long, bi-articular muscles have to cope with high internal forces and rapid changes in muscle length and mode of contraction. However, muscle strains have also been reported to occur during slow-lengthening muscle actions such as those performed by ballet dancers, but also during common daily activities. [5] Gastrocnemius is considered at high risk for strains because it crosses two joints (the knee and ankle) and has a high density of type two fast twitch muscle fibres. [2] A tear of the medial head of the gastrocnemius muscle is due to an eccentric force being applied to the muscle when the knee is extended and the ankle is dorsiflexed. The gastrocnemius muscle attempts to contract in the already lengthened state leading to tear of the muscle. [6] The soleus muscle on the other hand is injured while the knee is in flexion. Strains of the proximal medial musculotendinous junction are the most common type of soleus muscle injuries. Unlike gastrocnemius, soleus is considered low risk for injury. It crosses only the ankle and is largely comprised of type one slow twitch muscle fibres. Soleus strains also tend to be less dramatic in clinical presentation and more subacute when compared to injuries of gastrocnemius. [2] This condition frequently occurs in the middle-aged, poorly conditioned and/or physically active patient. [7]

Characteristics/Clinical Presentation[edit | edit source]

It is important to differentiate between muscle strains within the calf complex in order to formulate a correct prognosis, an appropriate treatment programme and prevention of recurrent injury. [8]

Gastrocnemius strains
Calf strains are most commonly found in the medial head of the gastrocnemius. [2] In an effort to contract, the forces of the eccentric movement on the already lengthened gastrocnemius muscle lead to injury at the myotendinous junction. The physical examination immediately after the injury reveals a palpable defect in the medial belly of the gastrocnemius just above the musculotendinous junction. [9] A sudden pain is felt in the calf, and the patient often reports an audible or palpable "pop" in the medial aspect of the posterior calf, or they have a feeling as though someone has kicked them in the back of the leg. Substantial pain and swelling usually develop during the following 24 hours. [1] Strains in the gastrocnemius are also referred to as a “tennis leg” as the classic presenttaion was a middle aged tennis player who suddenly extends the knee [2]


Soleus strains
Soleus is considered low risk for injury in contrast to the gastrocnemius asit crosses only the ankle and is largely composed of type one slow twitch muscle fibres. [2] Soleus strains tend to be less dramatic in clinical presentation and more subacute when compared to injuries of the gastrocnemius. Injury of the soleus muscle may be under reported due to a misdiagnosis of thrombophlebitis or lumping of soleus strains with strains of the gastrocnemius. [2] A soleus strain causes pain when activating the calf muscle or when applying pressure on the achilles tendon approximately 4 cm above the insertion point on the heel bone or higher up in the calf muscle. Stretching the tendon and walking on tip-toe will also aggravate pain. [10]


Plantaris strains
Plantaris is considered largely vestigial and rarely involved in calf strains, although it crosses both the knee and the ankle joint as well. [2] Rupture of the plantaris muscle may occur at the myotendinous junction with or without an associated hematoma or partial tear of the medial head of the gastrocnemius muscle or soleus. [4] Injury to the plantaris muscle can present with similar clinical features as those of the gastrocnemius and soleus muscle. [11]

Differential Diagnosis[edit | edit source]

Strains are most common during sporting activity, but pain in the lower leg could indicate medial tibial stress syndrome, achilles tendinitis, plantar fasciitis, muscles strains and/or joint sprains which can be caused by lack of extensibility of the plantar-flexors and decrease in ankle dorsiflexion. [12] The different degrees of muscle strains are discussed above. Other lower leg injuries related to sports with the same symptoms and treatment as a calf strain are discussed below. 

Runners often complain about lower leg pain along the posteromedial border of the tibia. [13] This is medial tibial stress syndrome (MTSS) or commonly known as shin splints. [14] The pain is described as tenderness located a few centimetres proximal to the medial malleolus, spreading proximally about 4 to 10 centimetres. The cause of MTSS may be associated with repetitive stress or an overuse injury.  

Pain located anterior or anteromedial of the tibia could indicate a tibial stress fracture, a typical injury seen in runners and footballers [14] [13] It can occur following abrupt changes in intensity, duration and frequency of training, but other personal and environmental factors can also contribute to this injury. Radiographs are initially negative, but with time fracture lines become visible. Operative treatment may occasionally be necessary, but it can be treated the same way as a calf strain: rest, restriction from aggravating activity, strengthening of the lower extremity musculature, NSAIDs and appropriate footwear.[11]

Repetitive exercise without adequate rest for recovery can cause chronic exertional compartment syndrome (CECS). [14] CECS begins with mild pain during periods of training and can disappear after training. In the latter stages, pain presents earlier, becoming more painful and of a greater duration forcing a halt in activity. Common complaints are; cramps, paraesthesia, numbness and weakness in the lower leg. CECS is caused by the increased intramuscular blood flow during exercise so compartmental pressure arises, capillaries become compressed and ischemia develops. 

Leg pain around the same area as a gastrocnemius strain can be caused by Popliteal Artery Entrapment Syndrome (PAES), an abnormal course of the popliteal artery. Medial and cranial migration of the medial head of the gastrocnemius can catch the popliteal artery and swipe it medially. This is called anatomical PAES, an abnormal relationship between the popliteal artery and the surrounding myofascial structures. Functional PAES is caused by muscle contraction, often active plantarflexion of the ankle that compresses the artery between the muscle and underlying bone. [15] See http://www.physio-pedia.com/Posterior_Knee_Pain

See also:

Achilles tendinopathy
Plantar fasciitis

Diagnostic Procedures[edit | edit source]

A thorough clinical examination and history may be enough to conclude a diagnosis, but it is often difficult to reach an accurate diagnosis due to the clinical being shared with other pathological conditions. Diagnostic imaging is usually necessary and ultrasound (US) is considered to be the gold standard. It can also be used to evaluate the degree and extent of the muscular lesion and to exclude other pathologies such as ruptured Baker's cyst and deep vein thrombosis. [16]

Ruptures are usually associated with the presence of fluid collection between the soleus muscle and the medial head of the gastrocnemius. This can occur with or without hemorrhage. The measurement of fluid collection gives us information about the extent of the lesion. The degree of the lesion (partial or complete rupture) can be defined by the distance between the two muscles. Axial US scans are the most useful for differentiating between partial and complete rupture, as it is possible to depict the whole muscle belly in one single image. [1]

A calf muscle tear is a most common injury in sports such as running, volleyball, tennis, etc. These sports require quick acceleration of changes in direction and are more susceptible for a calf strain injury. Muscle strains are graded as mild, moderate and severe. The more severe the strain, the longer the recovery time. Typical symptoms are stiffness, discoloration and bruising around the strained muscle. [10]


Grade I:
A first degree or mild injury is the most common and the most minor. A sharp pain is felt at the time of injury or pain with activity. There is little to no loss of strength and range-of-motion with muscle fibre disruption of less than 10%. A return to sport would be expected within 1 to 3 weeks. [13]

Grade II:
A second degree or moderate injury is a partial muscle tear halting activity. There is a clear loss of strength and range of motion. [13] with marked pain, swelling and often bruising. Muscle fibre disruption between 10 and 50%. 3 to 6 weeks is a usual recovery period for a return to full activity. [10]

Grade III:
A third degree or severe injury results in a complete rupture of the muscle and is often concomitant with a hematoma. [13] Pain, swelling, tenderness and bruising are usually present. Recovery is highly individualised and can take months before you are fully recovered for a full return to activity. [10]

Outcome Measures[edit | edit source]

  1. LEFS: Lower Extremity Functional Scale
  2. VAS: Visual Analogue Scale
  3. NPRS: Numeric Pain Rating Scale
  4. Muscle Strength testing: grade 0 is the lowest grade where the patient isn’t capable of doing any contraction of the muscle. Grade 5 is the highest grade where the patient is able to move his leg against a maximum resistance given by the therapist.

Examination[edit | edit source]

The physical exam isolates the site and severity of the injury. A combination of palpation, strength testing, and passive and active range of motion is necessary to help distinguish between strains of the soleus and gastrocnemius muscle.

Palpation of the calf should occur along the entire length of the muscles and the aponeuroses. This is required to identify swelling, thickening, tenderness, defects and masses if present. Strains of the gastrocnemius muscle usually present with tenderness in the medial belly or musculotendinous junction, while soleus strains often occur with lateral pain.

There are multiple techniques that exist to assess calf strains.
Considering that the origin of the gastrocnemius is situated above the knee (epicondylus lateralis and medialis femoris) and the origin of the soleus finds itself below the knee (caput fibulae), it allows the therapist to isolate the activation of the muscles by varying the degree of knee flexion. The soleus becomes the main source of force in plantar flexion, with the knee in maximal flexion. On the contrary, when the knee is in full extension, it is the gastrocnemius who provides more strength. This relationship allows for more accurate strength testing of the individual calf muscles and enables the examiner to describe which muscle has been injured.

Another similar method is used to test flexibility and pain during stretching and passive ankle movements. This technique allows us to determine the site of injury by isolating the gastrocnemius and soleus muscle. During the test, the knee is placed in maximal extension and thereafter in flexion while the ankle is passively dorsiflexed. This causes isolated stretch of the gastrocnemius and the soleus otherwise.

Additional testing that can be used during evaluation of calf strain includes the Thompson test for complete disruption of the Achilles tendon. It should also be noted that simultaneous tears of the gastrocnemius and soleus are possible, which can complicate the clinical picture.

If the diagnosis is still in doubt after these tests, the use of imaging can be helpful. The two choices of imaging are MRI and muskuloskeletal ultrasound (MSK US). Both can be used to confirm strain, localize the injured muscle and determine extent of injury.  [17] [18]


Medical Management[edit | edit source]

Calf strains rarely require surgery, but it is possible in extreme cases. Surgery can happen to the medial head of the gastrocnemius and also when the calf muscle is completely ruptured. However, rehabilitation will be recommended and also methods like RICE (see physical therapy management below). [3] (Level Of Evidence 5) An injection of local anesthetic and cortisone in and around the area, followed by a right stretching and stretch training treatment, will often take away some of the symptoms. When your muscle is torn there can occur a hematoma and it’s important to get this removed as quickly as possible, otherwise there may be complications such as myositis ossificans. This can be prevented with rehabilitation. When you’re unsure if your muscle is torn, it is best to visit a doctor who will refer you to a specialist to take an RX, MRI or ultrasonography for further investigation. [2] (Level Of Evidence 1b)

Prevention:

To prevent a calf muscle tear you can stretch these muscles every night. [1] (Level Of Evidence 1a) This will ensure that the gastrocnemius and soleus will not shorten and the joint mobility will increase.
When the muscles are extended, there can be a greater force delivered and the muscles are less tense which improves the blood flow. [19] (Level Of Evidence 2b) [4] (Level Of Evidence 1a)
Muscle stretching is easy to perform and has a low risk of side effects. It’s recommended to stretch one to three times a day for optimal results. [1] (Level Of Evidence 1a) (For more information about how to stretch, see physical therapy management).


Physical Therapy Management[edit | edit source]

The task of the physiotherapist contains:

  1. Settle down the pain
  2. Restore flexibility
  3. Restore strength

The principal treatment of a calf strain consists of rest and allowing time to heal, but in severe cases, people undergo surgery. In normal cases passive stretching, exercises for the antagonists and later the agonist and quadriceps exercises satisfy to heal the injury and reduce the pain. [3] (Level Of  Evidence 2a) At a later stage, patients can also be treated with massage of the calf muscles, ultrasound and electrical stimulation. [4] (Level of evidence 1a)

The aim of acute treatment is to limit bleeding and pain and to prevent complications. For the acute treatment we use the “RICE” principle that includes rest, ice, compression and elevation. [2] (Level of evidence 1b) The patient himself can apply ice in a towel to the painful area to relieve the pain with an endurance of 20 minutes. Otherwise a physiotherapist can use cryotherapy to decrease inflammation, pain and cell metabolism. Tape or a compressive wrap can be applied and the leg needs to be elevated. [3] (Level of evidence 2a) If major bleeding had occurred, it is necessary to be careful with the use of NSAIDs. NSAID’s have an antiplatelet effect which can increase bleeding as well as the early application of moist heat and massage does. [2] (Level of Evidence 1b)

After this, the patient can start with passive stretching exercises. Stretching promotes the range of motion of the plantar flexors, which is limited by shortness and contractures. [19] (Level of evidence 2b) The patient sits with the foot and lower leg straight out in front. It is important that the knee is in full extension so the gastrocnemius can be stretched. [2] (Level of evidence 1b) A calico bandage 8 to 10 feet long is twisted around the foot and held by the patient. The patient pulls the bandage towards him so a dorsiflexion of the ankle is performed. The stretching of the calf muscle is held in a phase of discomfort but without pain. The stretch is held for 10 seconds alternated with 10 seconds of relaxation. This cycle is repeated for 10 minutes. After this stretching protocol, 5 minutes of ultrasound therapy is applied at a dose of 0.5 to 2 watts per CM2 to change the viscoelasticity of the collages so any soreness caused by the stretching is relieved. Applying superficial heat simultaneously with a low load static stretch improves the flexibility of muscles. [3] (Level of evidence 2a)

The next step is 10 minutes of isotonic exercises for the antagonist (M. Tibialis Anterior, Mm. Peronei) and 10 minutes of exercises for the injured muscle. This whole process of stretching and exercises is carried out two to three times in the first 3 days after injury. It is important that the patient performs this process also at home. [3] (Level of evidence 2a) Lack of extensibility of the plantar flexors can cause decreases in ankle dorsiflexion and disturbs the gait. That is why patients should wear shoes with a low heel to perform correctly a heel-toe gait. [19] (Level of evidence 2b)

After forty-eight hours, ice is not an effective analgesic so short-wave diathermy is given for 20 minutes. A feeling of warmth is produced but no discomfort. A strain with abnormal swelling and bruising is treated with interferential therapy which produces a low frequency electric current to the injury. The aim of this method is to relieve the pain and to stimulate the muscle fibres. [3] (Level of evidence 2a)

Quadriceps exercises of 10 minutes are essential to protect the knee joint when returning to sports. When the muscle can be fully extended, we can switch from the passive stretch to a standing stretch. [3] (Level of evidence 2a) The patient stands with the foot of his normal leg 1 to 2 feet in front of the other foot and parallel to it. The heel of the injured leg is kept on the floor and the knee is straightened the whole time. The knee of the normal leg is flexed as far as the knee is forward over the forefoot. By flexing the knee, the soleus is elongated and the gastrocnemius is slacken. This stretch is continued for 10 sec. When the patient doesn’t feel the stretch, the front foot should be moved more forward until a phase of discomfort is felt. 

After 10 days the patient can perform isometric, isotonic and dynamic exercises to improve tensile strength. [2] (Level of evidence 1b)

Another treatment consists of vibration therapy (VT). Vibration therapy is applied specific on the area of injury and treats muscle strains and other myo-tendinous injuries that involve trigger points. [4] (Level of evidence 1a) Broadbent et al. suppose that VT stimulates the sensory receptors, but it causes also a decrease of inflammatory cells and receptors like IL6 and histamine. [20] The aim of this therapy is an increase in muscle strength, flexibility and extensibility. A SVT device (the V-Actor device) is placed on the injured area followed by a radial pressure wave (the D-Actor device) that gives impulses. The treatment duration is recommended for 4 minutes. After a VT treatment, jumping and running are forbidden for at least 3 to 6 weeks and NSAIDS are discouraged but other treatment routines can be continued. An advantage compared with other therapies like sound wave therapy and ESWT treatments, is that VT can be applied more frequently. [21]

Strains may cause long lasting pain, despite an adequate early treatment. The average time of treatment is nine days. The treatment is successfully accomplished when there is no more pain, when the calf muscle can be fully extended, when there is as much power in the lower leg and thigh as on the non-injured side, when ranges of knee and ankle are normal and when excessive tenderness has disappeared. [3] (Level of evidence 2a) Only when full extensibility and strength is achieved, the patient can return to his pre-injury activity.

Key Research[edit | edit source]

Millar, A. P., “Strains of the posterior calf musculature ("tennis leg")*.”The American Journal of Sports Medicine, vol. 7, no. 3, 1979, pp. 172-174. [Level of evidence 2a]

Ellen, Mark I., Jeffrey L. Young, and James L. Sarni. "3. Knee and lower extremity injuries." Archives of physical medicine and rehabilitation 80.5 (1999): S59-S67.

Bryan Dixon J. Gastrocnemius vs. soleus strain: how to differentiate and deal with calf muscle injuries. Current Reviews in Musculoskeletal Medicine. 2009;2(2):74-77. doi:10.1007/s12178-009-9045-8. [Level of evidence 1b]

Resources[edit | edit source]

All information used for this physiopedia subject is found on Pubmed, Physiopedia and Web Of Science. We also checked www.sportsinjuryclinic.net and www.moveforwardpt.com for global background information about calf strain.

Clinical Bottom Line[edit | edit source]

Pain in the calf muscle is often due to a strain however there are other conditions which could cause similar symptoms, including deep vein thrombosis and contusions. Treatment of muscle injuries usually has good outcome. Calf strains vary in healing time depending on how severe the strain is. In normal cases stretching and exercises satisfy to heal the injury and reduce the pain. Massage of the calf muscles, ultrasound and electrical stimulation can also be used in the treatment.

Recent Related Research (from Pubmed)
[edit | edit source]

The only recent relevant information related to calf strains found on Pubmed includes information about ultrasound elastography. The articles date from 2015 till 2016 so this reflects the interest in new research associated with ultrasound. [22] [23]

References
[edit | edit source]

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Kwak H-S, Han Y-M, Lee S-Y, Kim K-N, Chung GH. Diagnosis and Follow-up US Evaluation of Ruptures of the Medial Head of the Gastrocnemius (“Tennis Leg”). Korean Journal of Radiology. 2006;7(3):193-198. doi:10.3348/kjr.2006.7.3.193.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 Bryan Dixon J. Gastrocnemius vs. soleus strain: how to differentiate and deal with calf muscle injuries. Current Reviews in Musculoskeletal Medicine. 2009;2(2):74-77. doi:10.1007/s12178-009-9045-8. [Level of evidence 1b]
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Pedret C, Rodas G, Balius R, et al. Return to Play After Soleus Muscle Injuries. Orthopaedic Journal of Sports Medicine. 2015;3(7):2325967115595802. doi:10.1177/2325967115595802.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Spina AA. The plantaris muscle: anatomy, injury, imaging, and treatment. The Journal of the Canadian Chiropractic Association. 2007;51(3):158-165.
  5. ↑ Marc Roig Pull and Craig Ranson, Eccentric muscle actions: Implications for injury prevention and rehabilitation, Physical Therapy in Sport 8 (2007), no. 2, 88 – 97.
  6. ↑ Watura C, Harries W. Isolated tear of the tendon to the medial head of gastrocnemius presenting as a painless lump in the calf. BMJ Case Reports. 2009;2009:bcr01.2009.1468. doi:10.1136/bcr.01.2009.1468.
  7. ↑ Flecca D, Tomei A, Ravazzolo N, Martinelli M, Giovagnorio F. US evaluation and diagnosis of rupture of the medial head of the gastrocnemius (tennis leg). Journal of Ultrasound. 2007;10(4):194-198. doi:10.1016/j.jus.2007.09.007.
  8. ↑ Bryan Dixon J. Gastrocnemius vs. soleus strain: how to differentiate and deal with calf muscle injuries. Current Reviews in Musculoskeletal Medicine. 2009;2(2):74-77. doi:10.1007/s12178-009-9045-8. [L1b]
  9. ↑ Nsitem V. Diagnosis and rehabilitation of gastrocnemius muscle tear: a case report. The Journal of the Canadian Chiropractic Association. 2013;57(4):327-333.`
  10. ↑ 10.0 10.1 10.2 10.3 Ellen, Mark I., Jeffrey L. Young, and James L. Sarni. "3. Knee and lower extremity injuries." Archives of physical medicine and rehabilitation 80.5 (1999): S59-S67.
  11. ↑ 11.0 11.1 Meininger, Alexander K., and Jason L. Koh. "Evaluation of the injured runner." Clinics in sports medicine 31.2 (2012): 203-215.
  12. ↑ Knight CA., et al. (juni 2001). “Effect of Superficial Heat, Deep Heat, and Active Exercise Warm-up on the Extensibility of the Plantar Flexors.” Physical Therapy, Vol 81 (6), pp. 1206-1214. [Level of evidence 2b]
  13. ↑ 13.0 13.1 13.2 13.3 13.4 Nsitem V. Diagnosis and rehabilitation of gastrocnemius muscle tear: a case report. The Journal of the Canadian Chiropractic Association. 2013;57(4):327-333.`
  14. ↑ 14.0 14.1 14.2 Ellen, Mark I., Jeffrey L. Young, and James L. Sarni. "3. Knee and lower extremity injuries." Archives of physical medicine and rehabilitation 80.5 (1999): S59-S67. [Level of evidence 2a]
  15. ↑ Stager, Andrew, and Douglas Clement. "Popliteal artery entrapment syndrome." Sports Medicine 28.1 (1999): 61-70. [Level of evidence 3b]
  16. ↑ Flecca D, Tomei A, Ravazzolo N, Martinelli M, Giovagnorio F. US evaluation and diagnosis of rupture of the medial head of the gastrocnemius (tennis leg). Journal of Ultrasound. 2007;10(4):194-198. doi:10.1016/j.jus.2007.09.007.
  17. ↑ Bryan Dixon J. Gastrocnemius vs. soleus strain: how to differentiate and deal with calf muscle injuries. Current Reviews in Musculoskeletal Medicine. 2009;2(2):74-77. doi:10.1007/s12178-009-9045-8. [L1b]
  18. ↑ Marc Roig Pull and Craig Ranson, Eccentric muscle actions: Implications for injury prevention and rehabilitation, Physical Therapy in Sport 8 (2007), no. 2, 88 – 97.
  19. ↑ 19.0 19.1 19.2 Bartholdy, Cecilie, et al. "Local and Systemic Changes in Pain Sensitivity After 4 Weeks of Calf Muscle Stretching in a Nonpainful Population: A Randomized Trial." Pain Practice (2015). [Level of evidence 2b]
  20. ↑ Broadbent, Suzanne, et al. "Vibration therapy reduces plasma IL6 and muscle soreness after downhill running." British journal of sports medicine 44.12 (2010): 888-894. [L1b]
  21. ↑ Saxena, Amol, Marie St Louis, and Magali Fournier. "Vibration and pressure wave therapy for calf strains: a proposed treatment." Muscles, ligaments and tendons journal 3.2 (2013): 60. [L1a]
  22. ↑ Papadacci, Clement, Ethan Bunting, and Elisa Konofagou. "3D quasi-static ultrasound elastography with plane wave in vivo." IEEE Transactions on Medical Imaging (2016).
  23. ↑ Yanagisawa, Osamu, et al. "Effect of exercise-induced muscle damage on muscle hardness evaluated by ultrasound real-time tissue elastography." SpringerPlus 4.1 (2015): 1.


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