What is a Hamstring Strain?
The hamstring is a group of muscles which are behind the leg. They are made of three muscles, including the bicep femoris, semimembranosus and semitendinosus. These muscles insert into the pelvis and attach on the inside and outside of the knee via a tendon. Each muscle also has a intramuscular tendon, which is basically a attachment point for muscle fibres within the muscle belly.
The primary role of the hamstring is to bend the knee, but is also involves in decelerating the leg when sprinting and kicking. This is a common mechanism for injury to the hamstring as it acts as a brake to decelerate the leg in a lengthened position.
Previously hamstring strains were categorized by the size of the injury, being either grade 1, 2 or 3. We now understand the location of the injury is also an important consideration, as the tendon, junction between the tendon and muscle (known as myotendinous junction) and muscle itself often heal at different rates. Hence we now use a new classification system known as the BAIMC system.
Strains are classified based on their size;
Grade 0: Focal injury or DOMS with a normal MRI.
Grade 1 (Mild): Injury less then 10% in cross-section or longitudinal length of less then 5cm.
Grade 2 (Moderate): Injury between 10-50% in cross-section, of length between 5-15cm and less then 5cm of fiber disruption.
Grade 3 (Extensive): Injury greater then 50% of cross-section, of length greater then 15cm and greater then 5cm fiber disruption.
Grade 4: Complete rupture.
They are also classified based on their location;
Grade a: Muscle fiber (Myofascial)
Grade b: Muscle to tendon junction (Myotendinous junction) or connective tissue
Grade c: Tendon
Whilst MRI is used in most hamstring injuries within elite sport, in clinical practice we generally only use for injuries which appear to be located to the tendon, if there is a high recurrence or when attempting an accelerated return to sport.
How do I know I have a Hamstring Strain?
Hamstring strains generally have a mechanism or specific moment of injury. Typically this occurs during sprinting or kicking, but can also occur from overstretching.
Once an injury has occurred, the key signs which indicate a hamstring strain on assessment include;
A specific point of tenderness or discomfort.
Pain in that region when the hamstring is lengthened or stretched.
Pain in that when when contracting the hamstring.
How long does it take to return to sport?
There are a few assessment findings which can contribute to decision making for return to sport;
Length of discomfort on palpation.
Days until pain free walking.
Mechanism (especially if the injury is due to overstretching, which is related to a longer return to sport).
Available hamstring length on initial assessment,
How do I rehabilitate following a Hamstring Strain?
Protection / Improve Symptoms: Following the hamstring strain, there is typically a bleed and inflammatory stage for the first 48-72 hours alongside the development of muscle spasm to guard the region. Whilst icing may assist in symptom relief, it has not been demonstrated to increase return to play times following the injury. We have found compression can be useful in reducing muscle spasm and managing some of the bleeding which can occur following the strain.
Load Introduction: As a result of the inflammatory stage, a scaffold of scar tissue is laid over the region of the strain. This is a critical time in rehabilitation to commence a graded loading program to start building strength back into the strain site. Typically hip based strengthening exercises is better at loading the bicep femoris group (such as bridging and hinging variations), whereas knee based exercises are better at loading the semimembranosus and semitendinosus group (such as hamstring curl variations). We generally advice also recommencing general lower limb strengthening at this time such as loading the glute, calf, quadricep and core musculature. Running technique can also be a contributing factor for hamstring strains, so we can use this stage to commence drills to develop proper technique. Some of the key patterns that contribute to hamstring straights include overstriding and increased pelvic tilt among others. Running also also be generally introduced within the first week at low speeds as there is very little hamstring recruitment. Here some guidelines which we've put together to guide when to start running. Similar movement patterns such as side stepping and grape-vine drills can be introduced to maintain hip and groin loading.
Strength Accumulation: Building top end strength is a critical component of hamstring strain rehabilitation. A by-product of hamstring strains is a reduction in muscle fibre (fascicle) length. Adequate length of the muscle fibres is important as the hamstring is often injured in lengthened positions. As such, we often bias strengthening the hamstring in outer range positions (such as exercises load a Romanian deadlift or 45 degree hip extension). Another key role is selecting exercises that improve eccentric hamstring strength (such as nordic curls) due to the role hamstrings have in decelerating the leg in sprinting and kicking. There is also a theory that isometric (static based) strengthening exercise has a role in controlling end of range hamstring positions (such as Bosch Holds and long lever bridge holds). Building running loads is an important component of rehabilitation at this stage. Both linear, curved and change of direction running is important due to the different demands this place on the hamstring. Again, developing and building running technique in these positions is an important consideration.
Speed & Power: The final frontier for hamstring rehabilitation is introducing very-high speed running and sprinting loads. It's important that your hamstring strength is tested prior to introducing this. As your general running loads increase, it's also important to have a graded reintroduction to training loads. Once you have demonstrated the ability to sprint, completing a block of full training is essential prior to playing games. The duration of this block is dependent on the severity of the injury, but in general hamstring strains requiring more the three weeks should complete a full week of training prior to playing. Unfortunately there is an elevated risk of recurrence in the first month following return to sport, to monitoring your training and running loads is important. Alongside this, there is evidence which demonstrates maintaining regularly sprinting at least once a week alongside eccentric hamstring strengthening can significantly reduce your risk of recurrence.