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Hamstring Strain Article

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Here is an article I wrote for my website blog about hamstring strains, enjoy.

Why are Hamstring Strains so Common?

Out of all the muscles in the human body, the muscles making up the hamstring group are especially likely to become strained. Hamstring injuries are very prevalent in sports media coverage, as they are common in the athletic community. In sports like football, track & field, hockey, etc., hamstring strains are commonly the reason why athletes get put on the disabled list. Some of the reasons for this will be covered in this blog post.

What is a muscle strain?

First, it is important to understand the very definition of a muscle strain. A muscle strain is true to what most people imagine, it is a literal tearing of muscle tissue. In an athletic setting, the most common reason for muscle tearing is a combination of muscle lengthening and muscle loading. In other words, when a muscle is forced to control a load while lengthening, the muscle is put into a situation in which strain is more likely to occur. The medical community uses a simple model to denote the severity of a muscle strain. It is as follows:

- Grade I (mild), a small amount of tissue torn at a site on a muscle.
- Grade II (moderate), a significant amount of tissue torn at a site on a muscle.
- Grade III (severe), either most, or all, fibers torn at a site on a muscle.

What contributes to a hamstring strain?

The hamstrings are one of the prime movers for hip extension, along with the gluteus maximus muscles. The hamstrings are also the prime movers for knee flexion. This means that the hamstrings will lengthen during hip flexion and knee extension. Probability of hamstring strain increases the closer that hip flexion and knee extension reach their end ranges of motion. The probability is enhanced even further if both joints reach their end ranges simultaneously. If the hamstrings are lengthened at both joints while accommodating an external load, probability of strain is at its greatest.

Here are the key points describing the probability chain of hamstring strain:

- Muscle elongation through either hip flexion or knee extension.
- Muscle elongation through simultaneous hip flexion and knee extension.
- Muscle elongation through simultaneous hip flexion and knee extension, with accommodation of an external load.
- Muscle elongation through simultaneous hip flexion and knee extension, with accommodation of an external load in a very accelerated manner.

Other factors that contribute to the probability of a hamstring strain include:

- Weak hamstrings. This can be due to neurological impedance or lack of use (untrained).
- Fatigue. An individual can have very strong hamstrings, but if the muscles are in a fatigued state, strain is more likely to occur as the muscles are less able to control their range of motion. A fatigued muscle may allow hyper mobility of a joint and therefore allow the muscle to stretch past its tensile capacity, resulting in a tissue tear.
- Biomechanical imbalance. The body creates movement through chains of musculature, the hamstrings aren't the only muscles responsible for hip extension and knee flexion. The gluteus maximus is a very important muscle in hip extension as well. If the gluteus maximus is weak, the hamstrings may be forced to accommodate undue load which may result in tissue injury.
- Lack of flexibility. If the hamstrings are chronically tight, their ability to move through a functional range of motion is compromised. This means the end range of motion is lessened, so an incidence of strain through normal bodily movement is increased.

Muscle strains are most common when a muscle is engaged in its eccentric phase (or lengthening phase). An eccentric contraction is one in which a muscle controls a load while lengthening. In the case of the hamstrings, an example of an eccentric contraction occurs when an individual bends over to pick something off the floor. The hamstrings progressively let gravity take over as they lengthen to allow the torso to bend forward at the hips. The standing up phase would then be the concentric (shortening) phase of muscle function, because the hamstrings shorten to pull the torso back upright. Here is a detailed example of a situation in which an individual is likely to experience a hamstring strain. Note the many different important factors contributing to the hamstring strain:

A man picks up a heavy object off a high shelf. He has overly tight hamstrings as well as weak hamstrings. The individual bends over to put the object down, he does this by keeping his knees straight (lengthening the hamstrings at the knee) while bending over at the hip (further lengthening the hamstrings at the hip). The man realizes the weight he is holding is too heavy for him to slowly let down, but he doesn't want to drop it because it is fragile. The man does his best to not let the object fall to the ground, he slows the descent as much as he can (this implies a maximal eccentric contraction under significant load). He feels a "snapping" sensation in the back of his right upper thigh just before object is on the ground. The object is now safely down, but the man is now in obvious pain. All the primary factors were there for the strain to occur.

Why are the hamstrings more likely to be strained compared to other muscles?


There are several important reasons why the hamstrings are especially susceptible to strain.

1.) The hamstrings are multi-articulate, meaning they cross more than one joint. Because the hamstrings must control movement at more than one joint, the tensile capacity of the muscle tissue can be pushed past its limit if both joints lengthen simultaneously through an eccentric contraction. As mentioned at the beginning of the post, muscle strains are more common during an eccentric (lengthening) phase.

2.) The most common site of hamstring strain is near the proximal attachment at the ischial tuberosity, at the musculotendon junction. In general, injuries at the musculotendon junction are very common, because it is the site of the greatest tensile capacity differential (muscle tissue is not as strong as tendon tissue). The hamstring is composed of 4 different muscles. The biceps femoris long head (1), biceps femoris short head (2), semitendinosus (3) and semimembranosus (4). Each of these muscles has an independent distal attachment site*, but they all share a common proximal attachment site**. The hamstrings are large and powerful muscles that can create impressive acceleratory forces. Because high tensile forces must converge at a relatively small tissue site, where the multiple hamstring muscles converge to make a single tendon, the tissue can overload and tear.

*Both biceps femoris heads converge and share a distal attachment site at the head of the fibula.

** The biceps femoris short head doesn't attach to the ischial tuberosity like the other hamstring muscles. Rather, it doesn't cross the hip joint and it has its proximal attachment on the linea aspera of the femur.

3.) The hamstrings are a commonplace for muscular tension partly because of our societal behavior. We are a very sedentary society. Sitting for long periods in a "slumped" position can lead to biomechanial dysfunctions, which can include developed tension in the hamstrings. Looking through the lens of the lower-crossed syndrome model, acquired weakness in the gluteus maximus could potentially result in compensatory recruitment of the hamstring muscles for hip extension. Due to the over-recruitment of the hamstrings, the muscles are likely to increase in tone (tone is a neurologically adapted level of involuntary muscle contraction in a relaxed state). Hypertonic muscles (or muscles with a high level of tone) are prone to inflexibility. As discussed earlier, inflexibility can increase the chance of muscle strain.

How can massage be used to treat a muscle strain?


There are two primary massage methods that can be applied to treat a hamstring strain. Massage can also be used to prevent hamstring strains as well.

In the case of treating a hamstring strain, and the secondary problems that come along with it, here are some things that massage therapy can offer:

Facilitating muscle healing -

Deep transverse friction on the site of a muscle strain can be applied to stimulate fibroblast proliferation. Fibroblasts are cells that are responsible for creating collagen fibers. These fibers are the functional tensile units involved in muscle tissue. By facilitating collagen restoration, the muscle tear can heal more quickly. However, friction techniques are generally applied after the initial inflammatory period of the injury is over. The initial inflammatory period is generally described as lasting 2-3 days post-injury.

Forming functional scar tissue & encouraging tissue mobility -

Scar tissue forms as a result of fibrosis. Fibrosis is the body's way of healing a muscle tissue tear. Fibrosis is basically a process of the laying down of collagen fibers to bind up the site of injury and therefore restore the muscle's tensile integrity (or strength through elongation). However, the body's way of binding up a tear site can be "overzealous", as collagen distribution can be misaligned, overly abundant and cause binding to adjacent structures. Misaligned scar tissue impedes a muscles ability to stretch along its length, this means restriction from normal muscle elongation is made. Obviously such restriction is an adverse side-effect, as muscle inflexibility may have been an important factor in the cause of the original injury. By continuing a cycle of tension in the muscle, re-injury is more likely. Hamstring strains are notorious for recurring in athletes.

Deep transverse friction can be used to realign collagen fibers into a functional longitudinal direction with the muscle, therefore not only reducing adverse restriction in the muscle, but also increasing the tensile strength of the site of injury. Also, thoughtfully applied friction techniques encourage scar tissue mobility by freeing adhesions between the site of injury and adjacent structures.

Reducing muscle tension -

One of the most familiar and widely used benefits of massage therapy is muscle relaxation. Muscle relaxing techniques can be applied to the hamstrings and other posterior chain muscles not only for injury recovery, but also injury prevention.

If the hamstrings suffer a strain, the muscle is likely to become hypertonic due to the sympathetic nervous system activation involved with an injury to the body. Also, muscle splinting can occur in the hamstrings as to limit stretch and movement of the injured tissue. These states of increased muscle tension can linger after the muscle is fully healed. Residual tension can result in faulty biomechanics and can lead to re-injury of the muscle (because tension leads to inflexibility) as well as compensatory injuries in which other muscles have to overstretch (e.g. the lumbar musculature) to make up for the lack of ROM in the hamstrings.

Massage can be used to relax the hamstring muscles so that healthy biomechanics can be successfully reintegrated into the body's movement patterns after an injury. This is a situation in which a massage therapist can work very well as an adjunct professional with physical therapy/corrective exercise.

The simple injury-prevention aspect of massage therapy for hamstring strains is applied by restoring proper range of motion to the muscles through muscle relaxation and elimination of myofascial trigger points and adhesions. Facilitated stretching techniques can also supplement the process of muscle relaxation & elongation. Clinical assessment can also enlighten the massage therapist to possible underlying factors that may put an individual at risk for a hamstring injury.

Conclusion:

Hamstring strains are a prevalent injury within the athletic community. They are definitely given much attention by physical therapists, massage therapists, athletic trainers, personal trainers, etc. The key to remedying the problem is to devise a method for preventing hamstring strains all together, and then secondarily working on injury recovery methods. Clinical massage therapy has valuable things to offer in both the prevention and recovery of hamstring strains, as described in this post.

References:

Battermann N, et al. An anatomical study of the proximal hamstring muscle complex to elucidate muscle strains in this region. Int J Sports Med. 2011; 32(3):211-5.

Chaitow L, DeLany J. Clinical Application of Neuromuscular Techniques Vol 2: The Lower Body. Churchill Livingstone. 2002.

Elliot MC, et al. Hamstring muscle strains in professional football players: a 10-year review. Am J Sports Med. 2011; 39(4):843-50.

Heiderscheit BC, et al. Hamstring Strain Injuries: Recommendations for Diagnosis, Rehabilitation and Injury Prevention. J Orthop Sports Phys Ther. 2010; 40(2): 67???81.

Lowe, W. Orthopedic Assessment in Massage Therapy. Daviau Scott. 2006.

Lowe, W. Orthopedic Massage: Theory and Technique, 2nd Edition. Mosby Elsevier. 2009.

Malliaropoulos N, et al. Reinjury after acute posterior thigh muscle injuries in elite track and field athletes. Am J Sports Med. 2011; 39(2):304-10.

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Disclaimer:

This post is not meant to be a replacement for proper assessment, diagnosis or treatment by a physician. The information contained in this blog is for general informative purposes only. I am not responsible for how this information is used.
 
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