 Prevention of hamstring strains Click
to read the .pdf version John Orchard, Sport
Health, March 2003 Unfortunately for all
of our experience with hamstring injuries (and anyone who deals with sprint
athletes quickly gets plenty of experience in treating these injuries), there is
almost no proven method for preventing them. This is illustrated by the annual
AFL injury survey data, where hamstring strains are almost always the most
common and prevalent injury, with virtually unchanged injury rates over a
10-year period (1)
. This article will review some of the studies dealing with the issue of
hamstring prevention, but also will outline some speculative methods that may
help us in the future. There are some known
risk factors for hamstring strain, although the most certain risk factors –
age and injury history – are not reversible (2,
3)
. The most controversial risk factor is low strength (usually measured by
reduced hamstring to quadriceps (H:Q) ratio). Many prospective studies have
found a significant correlation between poor strength and risk of hamstring
injury (4-6)
. However, none of these studies measured past injury history as a
confounder, and it is possible that low H:Q ratio was highly correlated with
those athletes that had a past history of hamstring strain. A more recent study
with superior sample size to those cited previously suggested that H:Q ratio was
not a risk factor for hamstring strain (3)
. This paper used an eccentric protocol, which has become standard for
new generation isokinetic machines. However, a possible problem with this
methodology is that an eccentric protocol on an isokinetic machine can actually
cause a hamstring strain itself (7)
, so athletes may not give 100% effort when performing the eccentric
protocol out of self-preservation. Even if the weight of
evidence is highly suggestive that low H:Q ratio may be a risk factor for
hamstring strains, it is not readily apparent that attempting to reverse H:Q
deficits can reduce the incidence of hamstring strain. One study from two
decades ago suggested that this approach may work, but used a non-randomised
methodology (8)
. This has not been repeated by any follow-up studies, although recently
Tyler et al. reported similar results in adductors strains to the method of
Heiser et al. with hamstring strains (9)
. The lack of follow-up studies to support the success of Heiser’s
method, plus the lack of acceptance by clinicians makes it very unlikely that
the magic bullet for hamstring prevention is simply reversing strength deficits.
Another preventive
approach that is very unlikely to yield success is stretching. Almost all of the
studies that examined strength deficits have failed to find a correlation of
flexibility with injury risk (3-6,
8)
. Also, recent randomised controlled trails have placed major doubt on
stretching as a method for injury prevention (10,
11)
. A major confounder for flexibility studies is that athletes with
greater ‘speed’ show greater flexibility and probably also have a higher
injury risk (perhaps due to the greater ground reaction forces involved when
running faster). Distance athletes have reduced hamstring flexibility and may
actually may derive a performance benefit from this (12, 13)
, whilst it is known that hamstring injury incidence declines as running
speed is reduced (14)
. The ‘speed’ of running is probably a contributing reason why rugby
union and league players have a much lower hamstring injury risk than AFL
players, in that most rugby players are tackled within 10 metres of running with
the ball, so rarely reach maximum speed. The positions in the rugby codes which
do tend to reach top speed (full back and wingers) have higher rates of
hamstring injury than those playing in tighter positions. Even though the AFL
competition as a whole has a remarkably consistent rate of hamstring strains,
the hamstring injury rates of various teams show quite a high standard
deviation. In a recent editorial, I discussed how Malcolm Blight (when coaching)
focused on a heavy aerobic workload in the pre-season, which he obviously felt
improved end-of-season fitness based on the results of his teams over the years (15)
. It appeared that there was possibly a short-term cost in terms of
increased rates of hamstring injury (15)
. Another anecdotal
observation that is gaining in popularity is that afternoon running training
sessions may be a risk factor for hamstring injuries. Given that footballers and
sprint athletes need to do more than 7 sessions per week (when competition is
included), there will be occasions in the training schedule where both a running
training session and a weights session are performed on the same day. In theory,
the second of the two of these sessions will be performed in a fatigued state.
Since weights sessions do not have a significant risk of hamstring strain
injury, it is perhaps better to perform a weights session after the running
session. If players are ‘sore’ from a morning weights session and run in the
afternoon, then perhaps the risk of muscle strain increases. Terry Wallace was
quoted in the The greatest
challenge in hamstring prevention is in helping the athlete who has had multiple
muscle strains. An analysis of the AFL injury data showed a very high risk of
hamstring and calf strain for those older players who had suffered multiple
muscle strains in the past (2)
. It is fascinating that there is no correlation between quadriceps
strain and age, when the correlation is very strong for hamstring and calf
strains. Without giving away any secrets, there are good examples in most of the
popular sports of players who seem to be constantly tearing hamstrings (and/or
calf muscles). In the AFL, Robert Harvey, James Hird and Paul Kelly are some of
the highest profile examples in recent years, although the list is extremely
long. In the NRL, you can almost time the onset of the State of In discussing the
Steve Waugh case with Patrick Farhart, who was co-authoring the case history of
one of Steve’s injuries (a left calf strain) (16)
, Patrick drew my attention to a paper published by Chris Briggs in the
mid 1990s (17)
. This was a discussion of the lumbosacral ligament in pelvis, and showed
a correlation between L5/S1 degenerative changes and compression of the L5 nerve
root by the lumbosacral ligament. The lumbosacral ligament and its propensity
for extraforminal entrapment of the L5 nerve root was first described by Nathan
et al. and by other anatomists since (18-20)
. This anatomical configuration is quite possibly present in many of
these players who find that they have recurrent hamstring and calf tears despite
regular maintenance. If a nerve entrapment such as this were present, it could
also explain the correlation between hamstring injury risk and low strength, but
the difficulty in reducing the increased risk by strengthening. This anatomical
configuration also is compatible with an athlete that has no restriction of
lumbar and hip flexion, as it is most possible that any entrapment by the
lumbosacral ligament would be worse in extension. It is worth mentioning that
for many years ‘piriformis’ syndrome has been described as a cause of
recurrent posterior thigh pain, with inconsistent (although some excellent)
results from division of the piriformis muscle to release the sciatic nerve (21)
. Unfortunately, the
lumbosacral ligament is not easily accessible. The best method for reaching it
would probably be through an anterior approach, possibly with an abdominal
laparoscope. This type of surgery has recently been decribed (22)
. It remains to be seen whether it would be technically easy to divide
the ligament to free an entrapped L5 nerve root, and whether this procedure
would reduce the risk of hamstring injury without causing side effects. It also
remains to be seen whether such an entrapment could be confirmed with no
invasive methods (such as MRI) prior to surgery. If this theory is accepted as
justifying experimental exploration by a spinal surgeon, there will probably be
no shortage of elite athletes lining up to be ‘guinea pigs’ for a
lumbosacral ligament release. Hamstring injuries cause 15% of missed playing
time in the AFL and have an average recurrence rate of 30% for the remainder of
the season (1)
. The changes that occur subsequent to a muscle strain almost certainly
take months rather than weeks to reverse, so that it is likely that even those
players who successfully return to full competition soon after a hamstring
strain are doing so with subtle gait alterations that may affect performance or
predispose to other injuries (23)
. The most unlikely
scenario is that no progress will be made in the prevention of hamstring
injuries. Medical science gives us great confidence, and too many examples of
success where a condition seemed untreatable or unpreventable, for a problem
that is as common as hamstring strains to continue to confound us forever. This
is not to say that they will ever be eliminated, only that it would be more
surprising that in a further 20 years time that scientifically proven methods
for preventing hamstring strain had been established References
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