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IS CROSSING YOUR LEGS BAD FOR YOU?
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By
Claudia Hammond
14 October 2015
How do you like to sit on a chair? Many people
prefer to cross one leg over the other. In the 1980s, British comedian Kenny
Everett even made it his trademark – extravagantly crossing, uncrossing, then
recrossing his legs while dressed in a skirt and high heels, declaring it was
“all in the best possible taste”.
Others prefer not to cross their legs at all and even to “man spread” as it’s become known, sitting with their knees wide apart on public transport while the people either side of them are squashed. These men might have liked a rather curious publicity campaign launched in the US in 1999 called “The Great Cross-Out” where a dietary supplement company encouraged people to keep healthy by not crossing their legs for a whole day.
The list of suggested consequences includes raised blood pressure,
varicose veins and nerve damage, but is it true?
But is it really any healthier to avoid crossing
your legs? The list of suggested consequences of spending too much time with
one knee crossed over the other includes raised blood pressure, varicose veins
and nerve damage, but each of these deserves close examination.
Crossing the legs can put
pressure on the peroneal nerve at the back of the knee, which supplies
sensation to the lower legs and feet (Credit: SPL)
Of course it is true that if you spend too much
time in exactly the same position, eventually your leg or your foot can go
numb. This is because crossing the legs can put pressure on the peroneal nerve
behind the knee, which supplies sensation to the lower legs and feet. But if
you do give yourself pins and needles this way, it is only temporary.
Maintaining a particular posture for many, many
hours can however lead to a condition called peroneal nerve palsy resulting in
“foot drop” where you can’t lift the front part of your foot and toes. But when
a study from South
Korea examined a series of patients’ notes in order to
identify the chief causes, sitting on a chair with one knee over the other
didn’t feature. Sitting cross-legged on the floor for hours at a time did. In
reality long term numbness is an unlikely consequence of leg-crossing because
as soon as we feel uncomfortable we tend to move.
Sitting cross-legged on the
floor for hours at a time causes numbness (Credit: iStock)
So how about blood pressure? When you get it
checked, the doctor or nurse tends to ask you to rest your arm on the chair or
table and to uncross your legs, putting your feet flat on the floor. The fear
is that crossed legs might skew the reading by temporarily raising your blood
pressure. By 2010, seven studies had indeed found that leg crossing does result
in a higher blood pressure reading, while another study found it made no
difference. However, many of these studies were small and relied
on taking a blood pressure reading just once. One of the larger studies was
conducted at a hypertension clinic in Istanbul. Researchers there took several readings with legs crossed
and uncrossed. Again, blood pressure was higher when legs were
crossed, but crucially when the measurements were repeated just three minutes
after uncrossing the legs, blood pressure was back to the earlier levels. The
greatest rise in blood pressure occurs in people already being treated for high blood pressure.
Two possible mechanisms have been proposed to
explain why leg-crossing might lead to a temporary rise in blood pressure. One
is that the action of putting one knee over the other sends blood from the legs
up to the chest resulting in an increased quantity of blood being pumped out of
the heart, raising blood pressure. An alternative explanation is that blood
pressure rises because isometric exercise of the leg muscles (exercise without
the joints moving) increases the resistance to the blood passing
through the vessels. This might explain why crossing legs at the ankles doesn’t
have the same effect.
Crossing legs at the ankles
doesn't cause a rise in blood pressure, but it can at the knee (Credit: iStock)
In order to establish which of these explanations
was the most likely, a study in Nijmegen in the Netherlands took a number of
physiological measurements. The team found that resistance in the blood vessels
didn’t rise when the heart rate was low and the legs were crossed, but the
amount of blood leaving the heart did, suggesting that the increased blood
pressure is due to crossed legs
pushing blood up to the heart.
So crossing the legs does appear to cause a
temporary rise in blood pressure, but the evidence for any long-term
consequences simply isn’t there, with one exception. People at high risk of
blood clots are advised not to cross their legs for long periods of time
because for them, impeding the flow of blood could increase their risk of a deep vein thrombosis.
But even if crossing your legs doesn’t give you
high blood pressure in the long term, what about the idea that it can give you
varicose veins? The reasons why some people suffer from varicose veins and
others don’t is something of a
mystery. Usually tiny valves in the blood vessels prevent blood
from flowing back in the wrong direction, but if those valves become stretched
and weakened the blood can pool, resulting in the enlarged veins we
call varicose veins. Crossing the legs has not been demonstrated
to be a crucial factor. Whether or not you get varicose veins seems, partly at
least, to be down to genetics.
One study found that people who sat with their legs crossed for more
than three hours a day had poor posture
So if veins, blood pressure and nerves are not
affected by leg-crossing in the long-term, how about the impact on our joints?
One study found that people who sat with their legs crossed for more than three
hours a day were more likely to lean forward and to round their shoulders. But
the research relied on people’s own estimations of how long they crossed their
legs for. As I write this, I’m sitting at my desk and happen to have my legs
crossed, but I would have no idea how many hours a day I spend sitting in this
way. More recent research
published this year found that if people were instructed to
sit up straight while they crossed their legs the postural problems were
overcome. Of course whether that’s maintained when you have no experimenter
standing over you is another matter. Incidentally almost twice as many people
reported crossing their
right leg over their left knee than the other way around.
Crossed legs might bring
some benefits, building certain muscles (Credit: iStock)
Slouching doesn’t sound good, but if you are fan of
leg-crossing, you might like a rather curious study from the University Medical
Centre in Rotterdam which found that it could bring benefits. Researchers
examined young men and women as they sat with their legs either straight,
crossed at the knee or crossed at both the knee and the ankle at once. They
then simulated the exact angles of the posture in four embalmed pelvises, which
allowed them to measure exactly what our muscles do when we cross our legs.
They found that crossing the legs
at the knee increased elongation in the piriformis muscle running
behind the hip joint by 11% when compared with sitting with legs uncrossed, and
by 21% when compared with standing (interestingly the tension was slightly less
if the legs were crossed at the ankle too). The authors believe that this
increases stability in their pelvic joints in a similar way to tensing the
abdominal muscles does.
So if you like crossing your legs Kenny
Everett-style then you’re unlikely to do yourself any damage, provided you
don’t stay in the same position until your legs are numb. And whoever is
sitting next to you on the bus or the train will be grateful to you for taking
up less room than the man-spreaders.
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