A hamstring injury is a strain (tear) to one or more of the three large muscles at the back of the thigh (or their tendons at the back of the knee or in the pelvis).
What are the hamstrings?
The hamstrings are the three muscles at the back of the thigh. At the top they are attached to the 'sit bone' of the pelvis. The lower ends cross the back of the knee joint and are then attached to the bones of the lower leg:
- Semitendinosus - attaches to the back of the shin bone (tibia) on the inside of the back of the knee.
- Semimembranous - also attaches to the back of the shin bone (tibia) on the inside of the back of the knee.
- Biceps femoris - attaches to the top of the smaller bone of the lower leg (fibula) on the outside of the back of the knee.
They are involved in:
- Bending the knee.
- Tipping the pelvis back when you lean backwards.
- Twisting the knee when the knee is bent.
What is a hamstring injury?
A hamstring injury is a strain (muscle tear). They most often occur at the middle of the back of the thigh where the muscle joins its tendon or at the base of the buttocks.
The three grades of hamstring injury are:
- Grade I: a mild muscle strain - likely to recover in a few days.
- Grade II: a partial muscle tear.
- Grade III: a complete muscle tear or tear of an attachment - may take weeks or months to heal.
What causes hamstring injuries?
Hamstring injuries are common in all sports that involve short bursts of sprinting, suddenly stopping and changing direction and also jumping. So they are particularly common in football, rugby, baseball and track running.
Hamstring injuries happen most often at the end of the swing phase of running, just before the outstretched leg is put to the ground. At this point, the hamstring muscles have to suddenly shorten (contract) to bend the knee.
What makes a hamstring injury more likely?
There are many factors that are thought to make a hamstring injury more likely. Some are factors that you can do something about, such as:
- Muscle strength - mainly weak hamstrings (see below).
- Warming up - muscles work best and are less likely to be injured when they are warm. Doing some warming up exercises and keeping the legs warm with suitable clothing while warming up, are both essential.
- Tiredness - a footballer is more likely to injure their hamstring in the second half of a match than the first. Overall fitness is important.
- Core stability.
- Flexibility, although there is some debate about how important this is.
Other factors may not be as easy to change, such as:
- Previous hamstring injury - If you have already had a hamstring injury you are much more likely to have another one. Between 12 and 33 people out of 100 who have had one hamstring injury go on to have a second.
- Older age - a hamstring injury appears to be more common as you become older.
Neither weight nor BMI is thought to be a risk factor for a hamstring injury.
Importance of hamstring strength
Hamstring strength is probably the most important factor in hamstring injury. There is disagreement in the research as to whether it is an imbalance between the strength of the quadriceps muscles at the front of the thigh compared to the hamstrings that matters most or just the strength of the hamstrings themselves. Either way, it is essential to spend time working on your hamstring strength in order to avoid injury. A highly trained sportsperson will tend to do this as part of their training but recreational footballers or runners, for example, may not realise that they need to as well.
A specific exercise has been devised to increase the strength of the hamstring muscles at the point in running when they are at most risk of injury. It is called the Nordic hamstring exercise (see below - 'How to prevent a hamstring injury').
Symptoms of a hamstring injury
You may feel or hear a pop, followed immediately by severe pain in the affected leg after sudden lunging, jumping or sprinting. The muscle will often feel tight and tender, and go into cramp or spasm. In severe cases, there can be swelling and bruising. Walking may be painful. You may be unable to stand.
The back of the leg will feel tight, tender and possibly bruised. With more severe injury, swelling and a black and blue or bruised appearance will follow. In some cases there may be a gap in the muscle that you can actually feel by touching it.
Mild hamstring strains may not hurt too much. But severe ones can be very painful, making it impossible to walk or even stand.
Grade I injuries tend to be mild in that they tend to heal fully with only minor aggravation to the injured person, particularly in those whose sport doesn't put them at increased risk of further injury.
Grade II and III injuries take longer. Severely torn muscle can be debilitating for a long time and can be career-threatening to the professional athlete.
Hamstring injury treatment
Grade I-II minor to moderate hamstring injuries usually heal on their own. For the first 48-72 hours think of:
- Paying the PRICE - Protect, Rest, Ice, Compression, Elevation; and
- Do no HARM - no Heat, Alcohol, Running or Massage.
Paying the PRICE:
- Protect your leg from further injury.
- Rest your affected leg for 48-72 hours.
- Ice can be applied as soon as possible after your injury - for 15-20 minutes at a time. The cold is thought to reduce the flow of blood to the injured area and may reduce bleeding as well as reducing the pain and inflammation:
- Applying ice to an injury is very common advice but there is now some research suggesting that it might delay healing.
- There is more information on this and on applying an ice pack in the separate leaflet called Heat and Ice Treatment for Pain.
- Compression with a bandage can help to reduce pain and swelling. A tubular compression bandage will do the job well. You should only need this for a day or two.
- Elevation - keep your leg slightly raised while sitting to help reduce swelling.
- R is sometimes added to this list to make PRICER. R stands for Rehabilitation which is a really important part of the treatment for a hamstring injury - to get you back to normal and reduce the chances of you having another hamstring injury. You may need to see a physiotherapist or sports therapist for advice about the exercises to do but there is an outline below.
Avoid HARM for 72 hours after injury. That is, avoid:
- Heat - for example, hot baths, heat packs, saunas. Heat has the opposite effect on the flow of blood to ice. In other words, heat encourages blood flow. So, heat should be avoided in the early stages of an injury, when inflammation is developing.
- Alcoholic drinks, which can increase bleeding and swelling and decrease healing.
- Running or any other form of exercise which may cause further damage.
- Massage, which may increase swelling and bleeding. However, as with heat, after about 72 hours, gentle massage may be soothing.
- Painkillers, such as paracetamol: paracetamol is useful to ease pain.
- Anti-inflammatory painkillers: these medicines are also called non-steroidal anti-inflammatory drugs (NSAIDs):
- Note: National Institute for Health and Care Excellence (NICE), a well-known source of guidance for doctors in the UK, does not recommend that anti-inflammatory painkillers be used in the first 48 hours after an injury. This is because of concerns that they may delay healing. However, the evidence for this is old and of low quality. More recent studies suggest the benefits of taking NSAIDs for the short term, outweigh the risks.
- These medicines may have side-effects, such as an increased risk of bleeding and ulcers. They should only be used short-term, unless your doctor specifically says otherwise.
- Rub-on (topical) anti-inflammatory painkillers: again, there are various types and brands of topical anti-inflammatory painkillers. There is debate as to how effective these are compared with tablets. Some studies suggest that they may be as good as tablets for treating sprains. Others suggest they don't help. However, the amount of the medication that gets into the bloodstream is much less than with tablets and there is less risk of side-effects.
- Strengthening your hamstrings is the best protection against hamstring strain.
- In severe cases where the muscle is torn, you may need surgery. The surgeon will repair the muscle and reattach it.
Recovering from a hamstring injury
Recovering from a hamstring injury may take from days to months, depending on how severe the strain or tear is. A grade III injury can take several months to heal; you'll be unable to resume your usual training or play sport during this time.
Most hamstring injuries, even grade III injuries, heal without surgery. In severe cases, crutches or splinting may be necessary. In rare cases, where there is a complete rupture where the hamstrings join the pelvic bones at the top, surgery is necessary.
Lack of use, particularly if splinting, results in muscle shrinkage and the formation of scar tissue where the tear is healing. Excessive scar tissue prevents healthy muscle function, as it doesn't stretch and move as normal muscle does.
To avoid these complications rehabilitation exercises need to begin early (except grade III injuries):
- After a few days, once the pain has subsided, you should start to do regular gentle hamstring stretches followed by a programme of gentle exercise, such as walking and cycling.
- Always warm up before exercising and cool down afterwards.
- Stop if pain returns.
- To avoid injuring yourself again, you should only return to a full level of activity when your hamstring muscles are strong enough.
- Your physiotherapist or sports therapist will be able to advise you on returning to your sport and on a suitable graded exercise programme, which might include:
- Starting with decline treadmill running.
- Moving to steep decline treadmill running.
- Doing hamstring strengthening exercises using a pulley system to reduce the load.
- Doing regular hamstring exercises.
- When strength has returned, a gradual return to the desired sport can be attempted. Running should be re-introduced gradually.
- Full return is usually possible only after maximal flexibility and strength have been obtained.
Re-injury is extremely common. Athletes are highly motivated and are likely to have set personal goals for training, timing and performance. However, re-injury not only prolongs recovery, it also increases the risk of permanent damage.
How to prevent a hamstring injury
As with all sports-related muscle injuries the risk can be reduced by close attention to muscle strength. This is true both for preventing a first injury or a recurrence.
- A regular period of warming up your muscles before the intended athletic activity will reduce the risk.
- Improve the strength of the hamstrings. Examples would be:
- Horizontal power manoeuvres, such as repeated single leg broad jumps, combined with:
- Traditional resistance training that targets the hamstrings, such as hamstring curl.
- Nordic hamstring exercises (see below).
What is a Nordic hamstring exercise?
Nordic hamstring exercises are exercises that have been specifically designed to target the hamstring muscle at the point where is is most likely to be injured. They have been shown to reduce the risk of a first hamstring injury by 65% and the risk of a recurrent injury by as much as 85%. Some studies don't show that they are as effective as this but it would seem that it depends on how well the people doing them adhere to the exercise programme - in other words, if you don't do them regularly, they won't work as well.
They should be done regularly but only gradually increase how many are done and how often. They are intense and will cause delayed-onset muscle stiffness (DOMS) but this should not put you off doing them. (DOMS Is the medical term for the aching you can get in your muscles 24-48 hours after exercise.). They should NOT be done if you have a recent hamstring injury, unless advised to do so by your physiotherapist or sports therapist. They are best done with a partner.
How to do a Nordic hamstring exercise
- Kneel up with your hands in front of you.
- Your partner sits on the floor behind you and holds down your ankles.
- Then lower yourself towards the ground as slowly as you can.
- As soon as you can no longer hold yourself you drop down to the floor but use your arms to push yourself back up immediately, ie DO NOT use your hamstrings to get back up.
If you do not have a partner these exercises can be done by trapping your feet and then using your hands to walk yourself back up. However, this should be supervised by someone familiar with the exercises, at least initially.
What is the outlook for a hamstring injury?
The outlook (prognosis) is generally good, but can require a period of rest by avoiding running and athletic competition, followed by adhering to a rehabilitation programme of exercises. The length required for recovery varies depending on the severity of the muscle injury.
Further reading and references
Clark RA; Hamstring injuries: risk assessment and injury prevention. Ann Acad Med Singapore. 2008 Apr37(4):341-6.
Goode AP, Reiman MP, Harris L, et al; Eccentric training for prevention of hamstring injuries may depend on intervention compliance: a systematic review and meta-analysis. Br J Sports Med. 2015 Mar49(6):349-56. doi: 10.1136/bjsports-2014-093466. Epub 2014 Sep 16.
Freckleton G, Pizzari T; Risk factors for hamstring muscle strain injury in sport: a systematic review and meta-analysis. Br J Sports Med. 2013 Apr47(6):351-8. doi: 10.1136/bjsports-2011-090664. Epub 2012 Jul 4.
Petersen J, Thorborg K, Nielsen MB, et al; Preventive effect of eccentric training on acute hamstring injuries in men's soccer: a cluster-randomized controlled trial. Am J Sports Med. 2011 Nov39(11):2296-303. doi: 10.1177/0363546511419277. Epub 2011 Aug 8.
van der Horst N, Smits DW, Petersen J, et al; The preventive effect of the nordic hamstring exercise on hamstring injuries in amateur soccer players: a randomized controlled trial. Am J Sports Med. 2015 Jun43(6):1316-23. doi: 10.1177/0363546515574057. Epub 2015 Mar 20.