“Prolonged sitting in specific positions can also worsen circulation,” says Whiteley, a leading venous surgeon and founder of The Whiteley Clinic, adding that pooling blood can increase the risk of thrombosis.

Both experts advise moving, stretching, or standing up every 20 to 60 minutes to alleviate pressure.

So which sofa positions are the worst? Here are the hidden health impacts of the worst offenders – and how to fix them:

The armrest lean

According to Sofa Club’s poll, this is the most popular sofa position favoured by 43% of respondents. Leaning sideways against the armrest twists your back and neck in unnatural ways and throws off your weight distribution.

The fix: Chiropractor Chris Jolliffe, a member of the British Chiropractic Association (BCA) recommends: “Use a small cushion to elevate your arm and keep your shoulders level. Try not to stay in this position for too long and switch sides regularly.”

Slouched forward C-shape position

Canadian bio-mechanist Stuart McGill tested cadavers in various postures and measured the amount of force through the discs in the lumbar spine (lower back). He found that pressure was highest in slouched positions.

Bowden says: “Sitting slouched at the end of your flexion range in your lumbar spine and the thoracic spine (upper back) will apply pressure, if you are a gamer sitting in that position for a prolonged period, for example.”

Problems will be exacerbated if you also stick your head forward, for example, if your eyesight is poor or you are concentrating hard on something in front of you.

This position can also affect breathing. One 2016 study into the physical effects of slouching over smartphones found that people who hunched over for prolonged durations had partly impaired respiratory function and were predisposed to pathological conditions, such as headache, neck pain, shoulder pain and acid reflux.

The fix: Straighten your back and sit back on the sofa so your back is supported.

Crossed legs or one leg crossed on top of the other

Sitting with legs crossed, or one leg on the other, can cause a double whammy of problems.

“If you cross your right leg over your left knee, or vice versa, you have to bow your lumbar spine to the side. In theory that could contribute to things like postural scoliosis over a sustained period,” says Bowden.

Prolonged pressure on nerves, such as the sciatic or peroneal nerves, can lead to temporary numbness or symptoms of neuropathy in the legs or feet.

There has been speculation that the crossed-leg position can affect circulation but Whiteley disputes this and points out there is no good evidence to support this. However, he warns that sitting with legs tucked under you can restrict blood flow, especially behind the knees putting pressure on arteries and veins.

The fix: “Swapping positions on the sofa now and again is a good idea. No posture is a good posture for longer than 20 minutes,” says Bowden.

Perched upright

While those who sit ramrod-straight might think they are in a perfect position, Bowden explains that they are fooling themselves.

“Effectively, what this does is put the lower back in an arched and extended position at the end of its range, with the pelvis tilted forward. This creates muscle fatigue, because the muscles are holding you up in an artificial position.”

The fix: Lean back in a neutral position and hinge hips slightly back.

Lying on side with head on arm rest

According to Sofa Club’s poll, a third of people prefer this position, but unless your neck and spine are properly supported, this lounging style puts strain on your spine. Additionally, always lying on the same side can lead to uneven pressure.

Bowden explains: “This is like going to bed with your head on three pillows. Side-bending your neck in one direction habitually over a period of time is going to cause you a problem.”

The fix: Chiropractor Jolliffe says: “Use a pillow to support your neck and try to position your body towards what you’re looking at.”

Sitting in a neutral position

Even sitting in a neutral position can have implications if done for too long, as Whiteley explains. “If you sit down in a normal sitting position, your heart is significantly higher than your ankles, increasing the distance that the venous blood has to flow up the veins against gravity.”

The fix: “Putting the feet up on a foot stool or sinking down in the sofa to reduce the height of the heart, will aid the venous circulation,” says Whiteley.

Legs bent reclining

Sitting back in a reclined position with legs bent at the knee might seem comfortable, but inside your organs are less relaxed.

Nyland explains: “Slouching or reclining with your hips lower than the knees can compress the abdominal organs, which may slow digestion and contribute to issues such as acid reflux or bloating.”

The fix: Keeping legs straight. Jolliffe recommends using a lumbar support cushion behind your lower back.

The best sofa positions for…

Back pain

Samantha Shann, occupational therapist at Oak Tree Mobility and director of The Occupational Therapist Service, says: “Choose a sofa that supports the natural curve of your lower spine. If it lacks built-in lumbar support, try using a cushion to fill the gap between your sofa and lower back. One of the best sitting positions for lower back pain is sitting with your shoulders relaxed and back straight, without leaning forward. Place your feet flat on the floor, with your knees at 90 degrees.”

Posture support

The right furniture can support effective posture. For example, armchairs with arms, a high back and a seating height that allows both feet to reach flat on the floor can be more supportive for those who may be sitting for long periods of time. Rise and recline chairs, that are specifically measured to fit you, are most likely to ensure that your individual postural needs can be met now and in the long term.”

Leg swelling

Shann advises: “Elevating your feet above heart level can help to improve circulation and blood flow in your legs and reduce swelling in your feet and ankles. Raising your feet can also help to relieve pain in your legs, ankles or feet, because it reduces pressure on them and helps them to relax.”

Varicose veins

Lying flat is also an option, as Whiteley adds: “Being more horizontal will reduce swelling and discomfort in varicose veins or hidden varicose veins.”

Pregnancy

The advice for heavily pregnant women is to lie on their sides to stop the womb compressing arteries and veins in the back of the pelvis.