A Guide to Hamstring Strains
Out of all sports injuries hamstring strains are by far the most common.
They constitute a massive 24% of all injuries in soccer. Almost 1 in 3 of those injuring their hamstrings will suffer a re-injury with the same year.
Unfortunately hamstring injury rates remain on the rise, doubling in the last 20 years!
What are the Hamstrings?
The hamstring muscles are a group of 3 muscles which sit on the back of the thigh, crossing over both the hip and knee joints.
The muscles are the semimembranosus, semitendinosus and biceps femoris
Their more simple functions are to extend the hip and bend the knee. However they play a more complex and important role in movements such as sprinting, accelerating and kicking.
Hamstring strains tend to occur in 3 different ways.
Overstrain Injuries
When we run at high speed the hamstring has the work in a complex manner.
Keeping it simple during the stance phase of the running cycle (when your foot is in contact with the ground) the hamstrings will work together with your gluteal muscles to push your body forwards and your leg backwards.
As the leg starts to travel behind your body the hamstring muscles are put onto a rapid stretch, whilst they are still contracting hard to propel the leg backwards.
Towards the end of stance phase the hamstrings job will quickly change, to rapidly “braking” the leg in preparation for bringing it forwards again (swing phase).
Hamstring strains during high speed running are most likely to occur towards the end of swing phase due to high levels of hamstring muscle contraction and simultaneous stretch.
The biceps femoris muscle is most commonly involved with this injury type
Overstretch
Overstretch injuries occur if the hamstring is either rapidly lengthened or taken beyond its lengthening capability.
Common sporting mechanisms for this type of hamstring injury are from kicking or dancing or gymnastic movements which place large degrees of stretch on the muscle.
These are the most common hamstring strain seen outside of sport from slips trips of falls when the leg is rapidly extended.
The semimembranosus muscle is most commonly involved with overstretch injuries.
Repetitive Strain
Repetitive strain injury will likely have either no clear mechanism, or can occur from lower energy events.
These injuries can be explained using the load-capacity model (which we have explained in more detail in some of our other blogs). If the hamstring muscle is put under excessive strain for longer periods of time OR if activity levels are increased too quickly the muscles ability to tolerate load is exceeded, causing a strain to occur.
Hamstring strains will vary in their severity. Overstretch injuries are most likely to be more serious and take longer to recover from, overstrain injuries tend to sit in the middle, whilst repetitive strain injuries are likely to be of a lower severity.
Muscle strains are graded for severity. The models we use to classify muscle strains are now becoming more complex. Using the “British Athletic Classification” of muscle strain we can grade strains in severity 1 through 4 with subclassifications in each of these catagories.
But, to keep it simple……..
Grade 1 (Mild) Strains
Those sustaining this type of injury may not actually notice whilst participating in sport, or may initially feel a slight niggle.
Very small tear of less than 10% of muscle fibres. There is typically no decrease in muscle strength, pain and tenderness may not be immediately apparent. There will be no associated swelling or bruising.
Grade 2 (Moderate) Strains
Those sustaining this type of injury will immediately notice a grabbing sensation in the hamstring. They are likely not to be able to continue playing.
Significant tear of 10-50% of the muscle fibres OR involvement of the tendon. There will be significant immediate pain with this type of injury. Moderate swelling and some bruising may be present. There will be a loss of range of motion and strength.
Grade 3 (Severe) Strains
Those sustaining this type of injury are immediately likely to fall to the ground. There will be no chance of continuing to play.
These consistute a significant tear of more than 50% of the muscle .There will be severe loss of muscle strength with significant bruising and swelling.
Grade 4 Complete Tears
Those sustaining this type of injury are immediately likely to fall to the ground. There will be no chance of continuing to play.
These consistute a complete rupture of the muscle or avulsion of the tendon. There may be a palpable gap in the muscle. There will be severe loss of muscle strength with significant bruising and swelling is the days following the injury.
What to do if you have injured your hamstring
The management of hamstring strains depends heavily upon their classification. If you have suffered a hamstring injury it is important that you have it assessed by a competent physiotherapist. Too often lower grade injuries are either ignored and mismanaged. This contributes to the high reoccurrence rates that we currently see. We all know someone who is constantly straining their hamstrings!
Low grade strains can be rehabiltiated quickly and aggressively and a good physiotherapist may be able to identify factors that have contributed to the injury. Physiotherapy management in these cases is more geared towards preventing reoccurrence or reducing the risk of a more serious injury occurring.
Higher grade strains are a lot more serious. They may require an initial period of offload. In the most severe cases imaging and potential referral to an orthopaedic consultant may be required, though hamstring injuries are rarely managed with surgery these days.
Severe injury are likely to lead to significant losses in hamstring strength and function. Physiotherapy management in these cases is to work with you to restore hamstring strength, flexibility and functionality so that you can return to your previous level of activity.
Prevention is better than cure!
The biggest risk factor for hamstring strain is a previous hamstring strain!
Recurrence rates for hamstring injury are disproportionately high when compared with other muscle injuries. A big part of this is the unique nature of the muscle and the high demands that we place on it day to day. Inadequate rehabilitation and recovery from hamstring injury is therefore the biggest risk factor involved in having a new hamstring injury, at a different site or in a different muscle!
Research has enabled us to identify other risk factors for hamstring injury.
Significant risk factors include
Age - risk can start to increase as young as 24!
Previous ACL injury (increases risk by over 70%!)
Previous calf strains (increase risk by over 50%)
Hamstring strength imbalances
Quadricep to hamstring strength ratio imbalances
Other risk factors can include
Neurological sensitivity
Rapid increases in sprinting loads or volumes
Inadequate warm up
Choice of sport (those that involve sprinting are at highest risk)