For footballers, hamstring injuries are a hazard of the trade.
They’re a nuisance injury which can cost weeks, sometimes even months of a season.
In particularly bad cases, they can change the course of a career.
But what actually are hamstrings and why are we always talking about them in football?
Technically, it isn’t one muscle. The hamstring is actually a group of three different muscles,
which run from the pelvis to the knee, down the back of the thigh.
Collectively they’re known as the hamstring, and it works by elongating and contracting
with the flexing of the knee, with the aim of controlling the swing of the leg.
To simplify, consider a running motion:
After a leg leaves the ground, it encounters three stages as it begins to move forward,
entering what’s known as the Swing Phase.
Stage One is the initial swing.
Stage Two the mid-swing…
…and – lastly – Stage Three, the terminal swing, which occurs just before the foot returns
to the ground.
At this point, the hamstrung is fully extended. At the same time, it’s also contracting,
working to control the leg, and the conflict between those two movements generates what’s
known as eccentric stress upon the muscle.
Too much stress and the muscle fibres tear, causing injury – with the extent of the
tear determining the severity.
Grade One is a 25% tear in the muscle. A Grade Two is when the tear is between 25% to 75%.
And the most serious case, Grade Three, refers to anything above, including a complete rupture.
The most at-risk athletes are sprinters. Given their dependence on power and explosiveness
that’s self-evident, but any sport that involves quick changes of direction, or rapid
acceleration or deceleration involves a high instance of hamstring injuries.
That, of course, includes football. In a 2012 study in the Journal of Sport & Health Science,
entitled Injury Rate, Mechanism, and Risk Factors of Hamstring Strain Injuries in Sport,
it was estimated that – on average, during an English professional football season – hamstring
injuries accounted for 90 missed days and 15 missed matches per club.
Logically so. Players must change directions and speeds regularly, but the nature of the
sport also involves a further risk – as Dr Raj Brar of 3CB Performance explains.
“When you kick and the knee is straightening, the hamstrings have to slow down the kicking
motion to control it.”
In other words, the hamstrings provide the stability necessary to strike a football properly
and precisely.
The cost of that facility, however, is that every pass, shot or even tackle is a potential
source of eccentric stress. And the hamstring’s capacity to cope with that is determined by
what’s known as its Load Tolerance.
Dr Brar defines two different types of load tolerance – one that describes what a muscle
can bear at any given moment, but another which measures what it can withstand over
time, with the effects of fatigue or cumulative endurance.
Like a bucket filling with water, however, whether Load Tolerance is exceeded drop by
drop or with a sudden burst, the effect is the same, as are the consequences.
So, what determines load capacity?
Factors such as age, general health and physical conditioning are highly instructive, but so
is injury history, and that’s really what makes damaging hamstrings so hazardous for
a player.
When a muscle suffers a tear, the body repairs itself with scar tissue. Scar tissue isn’t
as flexible as the natural tissue it replaces and, as a result, a build-up results in a
loss of elasticity within the muscle and a restricting effect on movement.
It also decreases Load Tolerance and increases the likelihood of reoccurrence. Dr Brar references
high-level research that estimates that on returning from a hamstring injury, a player
is then at twice as much risk of suffering another for the next year.
So, they’re notorious for interrupting careers, but sometimes they even change them too.
Barcelona’s Ousmane Dembele has had four significant injuries in that area since arriving
at the club in 2017 and rupturing his hamstring on his debut.
The former Liverpool forward Fernando Torres once had three hamstring injuries in the same
2008-09 season and, most famously, the serious tear Michael Owen suffered at the age of 19
was not only a precursor to a succession of further injuries, but also necessitated an
adaption to his playing style.
However, those after-effects don’t always have a single cause. Sometimes, they’re
attributable to the damaged muscle itself. In other instances, secondary factors might
be responsible.
The player’s training application might drop. Their strength and conditioning program
may be insufficient. Sometimes their intensity in games themselves might fall. In all three
cases, that could be partly attributable to the psychological effect of too many injuries,
or a loss of confidence in the muscle.
Or the explanation could be simpler: if a player isn’t properly committed to recovery
and isn’t appreciative enough of the nutritional and lifestyle factors that determine how well
the body heals, then a hamstring injury is more likely to have a longer-term legacy.
Whatever the cause, that group of muscles is a player’s career. In an interview with
The Telegraph, Michael Owen once said that the severity of the injury he suffered had
left him ‘running on a third (of his) power.
Fernando Torres was more definitive. Following his injury blighted 2009, his hamstring let
him down on the biggest stage: despite playing just 24 minutes as a substitute, it would
tear at the end of Spain’s extra-time win over Holland in the 2010 World Cup Final.
It was the muscle ‘he lived by’, he said in his autobiography. It was also the muscle
that expedited his descent from the game’s peak.
And the same would be true for almost any footballer, especially those who depend on
speed and acceleration for their livelihood.