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Muscle strain

Also called muscle strains, muscle strain injury, muscle tear, indirect muscle injury, traumatic muscle injury

An overstretched or torn muscle, the general case behind hamstring, calf and hip flexor strains. How reviews define and grade it, who it affects, how long elite players were out, and what reviews of injections found.

Region
Across the body
Muscles
hamstrings, adductors, quadriceps, gastrocnemius, soleus
Updated
October 15, 2026
Reviewed
October 15, 2026 · how entries are checked

What it is

What the name covers

A 2023 review defines traumatic muscle injury as damage to muscle tissue that can cause a loss of function1. It splits these injuries in two1. Indirect, non-contact injuries are strains or ruptures, often from a muscle being activated as it lengthens1. Direct injuries come from an outside impact, as a contusion (a bruise) or a cut1.

The 2013 Munich consensus statement, a report of what an expert panel agreed, calls “strain” one of the most used terms for these injuries9. It adds that the term still has no clear definition and is used in very different ways9. Its authors do not recommend the word and propose “tear” for injuries with torn muscle fibres9.

Where it tends to happen

A 2020 statement paper says lower-limb muscle injuries are frequent in sports built on sprinting, jumping, sudden turns and kicking10. It says non-contact strains are typically thought to happen where muscle joins tendon, when force exceeds what the tissue can bear10. The Munich statement lists features of muscles that are often injured9:

  • they often cross two joints, or have a more complex build9;
  • they do eccentric work, meaning they work while lengthening9;
  • they hold mostly type 2 fibres, the fast-contracting kind9.

The same statement reports that up to 96% of muscle injuries in football happen without contact9. Contusions are more common in contact sports such as rugby, American football and ice hockey9.

How injuries are graded

A scoping review of sudden non-contact muscle injuries in adults who play sport found 24 classifications in 37 studies from 2010 to 20223. Most were made for hamstring or other lower-limb injuries3. Six systems, among them Munich, BAMIC and MLG-R, made up 70% of the reports3. The review concluded that no classification or set of terms is agreed, so outcomes by grade differ between studies3.

Three of the six sort injuries in different ways9,11,12:

SystemHow it sorts an injury
Munich (2013)Functional disorders with no visible tear, against structural tears, from partial to total, and avulsions, where a tendon pulls off its bone9
British Athletics (BAMIC, 2014)A grade from 0 to 4 on MRI, plus a site letter: a at the fascia, b where muscle meets tendon, c inside the tendon11
MLG-R (2017)Four letters: how it happened, where it is, how severe it is, and how many times that muscle was re-injured12

Who it affects

A 2023 review states that traumatic muscle injury can affect people at any stage of life1. The counts below come from elite sport:

Who was studiedWhat was found
2,299 male professional footballers, 2001 to 2009Muscle injuries were 31% of all injuries2. A player had 0.6 a season on average, about 15 a season for a squad of 252
89 European professional men’s teams, 2001 to 2013Muscle injuries were 32% of 17,371 injuries13
44 studies of professional men’s football, pooledMuscle and tendon injuries were the most common type, 4.6 per 1,000 hours against 8.1 for all injuries14
596 players in 15 elite European women’s teamsThigh muscle injuries were the most frequent; hamstrings were 12% and quadriceps 11% of 1,527 injuries15
13 international athletics championships, 2009 to 2019344 lower-limb muscle injuries, 36% of injuries in competition16

In the cohort of 2,299 footballers, 92% of muscle injuries were in the hamstrings, adductors, quadriceps and calf2.

Four views of the bones of the right leg, the lower spine and the pelvis, with four groups of muscles drawn on them. In each view one group is orange and the others are pale pink. From behind, the orange hamstrings run down the back of the thigh from the bottom of the pelvis to just below the knee. From the inner side, the orange adductors run from the pelvis down the inner thigh. From the front, the orange quadriceps cover the front of the thigh above the kneecap. From behind again, the orange calf muscles fill the back of the lower leg below the knee.
The hamstrings, adductors, quadriceps and calf muscles of the right leg, one group coloured in each viewRendered by Your Basic Trainer from the Open 3D Model by AnatomyTOOL, which builds on Z-Anatomy and BodyParts3D (Database Center for Life Science). (source, CC BY-SA 4.0). Rendered from the 3D model in four labelled views with only the bones and four muscle groups shown (hamstrings, adductors, quadriceps and calf), one group coloured orange in each view and the other three faded

A 2020 statement paper says strain rates have held steady for decades in football and Australian football10. Hamstring and calf strains rose slightly over that time10.

What goes with a higher rate

In a cohort of 1,401 male professional footballers, previous injury, older age and the kicking leg went with higher muscle injury rates17. The same injury in the previous season went with higher rates in all four main groups17. In Australian Football League data from 1992 to 2014, a recent injury of the same kind was the strongest risk factor for each main strain18.

How often it comes back

In the cohort of 2,299 footballers, 16% of muscle injuries were re-injuries, which kept players out significantly longer than first injuries2. The Australian Football League data covered 3,647 muscle strains18. The risk of a recurrence in the first match back differed by muscle; for all strains combined, it fell gradually after that18:

Recurrence risk in the first match back (%)Hamstring9 Groin6 Quadriceps5 Calf2
Recurrence risk in the first match back (%). Bars start at zero; the table below gives each value with its source.
StrainRecurrence risk in the first match back (%)
Hamstring918
Groin618
Quadriceps518
Calf218

What studies found

How long elite players were out

One study tested the Munich system on 393 thigh muscle injuries4. They came from 31 European men’s professional football teams in 2011/124. Two-thirds were structural, and these kept players out longer than functional disorders, whose median was 5 to 8 days4. Among the tears, median time out rose with size4:

Median days outMinor partial tear13 Moderate partial tear32 Subtotal or complete tear, or tendon avulsion60
Median days out. Bars start at zero; the table below gives each value with its source.
Tear, Munich classMedian days out
Minor partial tear134
Moderate partial tear324
Subtotal or complete tear, or tendon avulsion604

In the same study, time out did not differ significantly between the front and back of the thigh4. Of the injuries, 12% were re-injuries, and the injury class showed no significant link with re-injury4. Of injuries assessed both by examination and on imaging, 77% were judged tears on examination, but MRI showed a tear in only 29%4.

In the UEFA Elite Club Injury Study of professional football, structural calf, hamstring and quadriceps injuries each had a median of 13 days out19. Its authors suggest muscle tissue may need a certain time to heal before return to play, whichever group is hurt19. A systematic review covered 11 cohort studies of 468 athletes with 574 muscle injuries graded with BAMIC20. Every study linked grade or site with return to play20. Fewer linked them with re-injury: 2 of 4 studies by grade and 3 of 4 by site20.

What MRI adds

In the 89 European men’s teams, time out tracked the MRI grade of thigh injuries13. A 2026 systematic review of 961 injuries in male professional soccer players found that the MRI signs linked to longer return differed by muscle group21. In hamstrings, involvement of the tendon or its junction with muscle went with longer return, while oedema (fluid swelling) predicted poorly21. The same review concluded that MRI is an important but not stand-alone part of return decisions21.

Between 50% and 90% of athletes back at play 29 to 49 days after a muscle injury still showed an abnormal MRI signal22. That figure comes from a 2019 Italian consensus statement on football22. The same statement reports that MRI and ultrasound signals returned to normal after about 6 months on average22.

How the tissue heals, and early loading

The muscle page covers the three phases of repair that a review describes23. A review states that minor injuries such as strains heal on their own, while severe ones form scar tissue that impairs function23.

A 2023 review states that care for muscle injury had moved within 5 years from rest and protection to early activity and gradual loading1. One randomised trial, which assigns people to groups by chance, compared an early with a delayed start to an exercise programme24. It enrolled 50 recreational athletes with a severe acute thigh or calf strain24. PubMed’s record of its 2018 paper lists seven funders, among them the Novo Nordisk Foundation, Denmark’s Ministry of Culture and Bispebjerg Hospital24.

In the same trial, the authors reported that the early start sped up recovery24. Strength was similar in both groups at 5 weeks, 3 months and 6 months, and one re-injury was recorded24. The authors said their imaging and strength measures did not explain the faster recovery, as both groups recovered structure and function alike24. In both groups, MRI still showed higher blood flow in the injured muscle than in an uninjured one after 6 months24.

A 2005 review said that, though these injuries are common, few clinical studies had looked at managing them25. A 2020 statement paper rated most outcomes very low to moderate in quality10. The same paper found the research mainly on hamstrings, with little on quadriceps, adductor and calf injuries10.

Injections and medicines

A 2014 systematic review states that injections are widely used for muscle injuries but have only limited evidence that they work26. A 2023 review agrees, describing very limited evidence for the many medicines and injections used1. The 2014 review found strong to moderate evidence that numbing drugs and NSAIDs (anti-inflammatory painkillers) are toxic to muscle when injected into it26.

Reviews of platelet-rich plasma injections (made from a person’s own blood) for acute muscle injuries differ on how firm the gain in return time is5,6,7,8:

  • Grassi 2018, six randomised trials, 374 patients. Return came about 7 days sooner overall, but not significantly sooner in the two double-blind trials5. Double-blind means neither participants nor assessors knew the groups. Patients were not blinded in four of the six trials5.
  • Sheth 2018, five randomised trials, 268 patients with grade I or II injuries. Return came about 5.6 days earlier, with no significant difference in re-injury6. With hamstring strains alone, return time did not differ6.
  • Bensa 2026, nine randomised trials, 474 patients. Return came a mean 7.5 days sooner, including in the double-blind and hamstring trials, with no difference in re-injury7. It judged five trials at high risk of bias and urged caution7.
  • Kobayashi 2026, an umbrella review of eight systematic reviews in athletes. Re-injury risk was lower with platelet-rich plasma, a risk ratio of 0.84, with high certainty of evidence, meaning reviewers were sure of it8. Return came 4.4 days sooner, but not significantly so, with low certainty8.

Deciding when to return

The Italian consensus came from a Delphi study of 66 experts, a method that polls experts in rounds22. It separates two stages22. Return to training is partial rejoining of the team; return to play is full, unrestricted training and matches22. It said return decisions rested on expert opinion, and rated its own advice as level IV evidence, a low rung, grade D22.

A 2026 systematic review of football studies also found that the decisions rest on expert opinion, not validated outcomes27. Across its ten studies, the most common criteria were no pain, at least 90% strength symmetry and functional tests, and re-injury was rarely reported27.

Connections

Three published pages each cover strains of one muscle group19,28,29:

  • Hamstring strain: the most frequent injury in Australian Football League data from 1992 to 201228.
  • Calf strain: 818 first-time structural calf injuries in elite football kept players out a median of 13 days19.
  • Hip flexor strain: in 33 male athletes with an acute hip flexor injury on MRI, 16 were in the rectus femoris29.

The four groups named in the football cohort have their own entries: hamstrings, hip adductors, quadriceps, and the calf’s gastrocnemius and soleus2.

The fascia page covers the BAMIC site letters11. A 2023 meta-analysis found moderate evidence of a better outlook for “b” injuries than “c” ones30. The same review found no strong evidence that tendon involvement inside the muscle changed return time30. It rated eight of its nine studies at high risk of bias30.

Muscle strain is one kind of injury to

Muscle strain is the general case of

Muscle strain involves

Muscle strain is graded in one system by whether it involves

Sources

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Every source the library cites

Changes

  • First published.