HAMSTRING MUSCLE INJURIES BY LEE HERRINGTON, PHD MCSP CSCS

WHAT CAUSES HAMSTRING INJURIES? There are a number of predisposing factors pertaining to hamstring muscle injuries which a clinician and a sports performer must be aware of, these include; the particular anatomy of the hamstring muscle group, muscle flexibility, muscle strength imbalances, lumbo-pelvic status and running mechanics.

Anatomy

The hamstrings are a group of three muscles (Biceps Femoris, Semitendinosus, Semimembranosus) these muscles are bi-articular in that they cross two joints; the hip and the knee. This means their action involves controlling motion at two joint simultaneously, to further complicate this Biceps Femoris also has dual innervation which means it is supplied by two nerves further complicating its action and control of this muscle.

Muscle flexibility

Despite the considerable hype around this issue, there is little strong or convincing research evidence to support either the use of stretching exercises for the hamstrings to prevent injuries or lack flexibility increasing the risk of injury. This might in part be due to the fact that the majority of hamstring muscle injuries occur during rapid changes in type of contraction i.e. eccentric to concentric or velocity of the limb during the cross-over from swing to stance phase for instance, at this point the hamstring muscles are nowhere near their full range of movement. It could also be the case that athletes who regularly statically stretch their hamstring muscles are at increased risk of injury. Static stretching has been shown to acutely decrease the performance of muscle and increase resting tone in the muscle. Furthermore, inappropriate stretching, for instance involving excessive lumbar flexion could irritate and damage elements of the lumbar spine and nervous system, which as mentioned later could increase the predisposition to injury. It has also been

TO SUPPORT THE USE OF STRETCHING EXERCISES FOR THE HAMSTRINGS TO PREVENT INJURIES

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THERE IS LITTLE STRONG OR CONVINCING RESEARCH EVIDENCE

It is very rare that a weekend of sport goes by without a player at a top sporting club or athlete injuring their hamstring muscle. It is by far the most common muscle injury with injury rates as high as 10-15%. Perhaps even more significant than this is that the reoccurrence rate for another hamstring injury is anywhere between 12-34% for those sports people who have suffered an initial hamstring injury. The question which needs answering then must be what causes hamstring injuries? And equally what is going wrong with the rehabilitation of these injuries so as to not prevent their reoccurrence?

the author’s experience that those athletes who stretch excessive and often have exceptional ranget of movement compared to their team mates are often the ones who most frequently suffer muscle injury.

Muscle strength imbalances Unbalanced quadriceps action due to excessive muscle hypertrophy of the quadriceps (as opposed to weakness of the hamstrings) has been cited as a potential cause of hamstring muscle injuries. The excessive development of quadriceps strength in certain sports, particularly those incorporating heavy squatting exercises, or short burst sprints for example, may fail to address hamstring strength development increasing the load produced by the quadriceps the hamstrings must overcome to decelerate the limb. A second muscle imbalance which also needs considering in relation to hamstring muscle injuries is that of hamstring activity to Gluteal muscle activity during hip extension. Previous research has shown the hamstring muscles to produce slightly less than 50% of the force during hip extension with Gluteal muscles (principally Gluteus Maximus) producing the rest. If the Gluteal muscles are deficient either in turns of their recruitment or strength than the relative load will be increased on the hamstring muscles.

Lumbo-pelvic status Two potential areas related to the lumbo-pelvic function can have a direct bearing on hamstring injuries the first is

sportEX dynamics 2009;20(Apr):20-22