The health hazards of summer sandals

They may keep your feet cool, but wearing the wrong sandals – including Birkenstocks – could give you a wide range of physiological problems

Summer sandal season always presents podiatrist Helen Branthwaite with new patients, but this year her own mother was among them, having purchased a pair of pale blue Birkenstocks only a few weeks before. 
“My younger sister had some and then my mum bought some too,” says Branthwaite.“She was totally attracted by the image around them.” 
Branthwaite, the musculoskeletal lead for the Royal College of Podiatry, had tried in vain to warn her mother against using the sandals; with their lack of cushioning and arch support, as well as the absence of a strap around the back, her new Birkenstocks were just too much of a leap from her usual supportive Scholl sandals. Days later, her mum was complaining of foot pain. 
“Mum was used to having a drop at the front of the shoe so that it’s lower than the back.” says Branthwaite. “The Birkenstock is much flatter, which forces her to stand and walk differently. 
“So it created an alteration in the ankle and the way that her muscles work. She had to use the toes more to keep them on, and stained the tendons.” 
It wasn’t the Birkenstocks’ fault per se, says Branthwaite. When diagnosing any shoe problem, she looks for a mismatch between the function, anatomy and adaptation of the wearer and their shoe style. 
“As soon as you put any shoe on it changes the way that you move. The way you progress through the foot, the forces on the foot and the way that the limb and spine move,” she explains. 
Podiatrists joke that summer and flip flops means it is heel pain season. 
“I always see more cases of plantar fasciitis (heel pain) at the end of summer, and the majority are triggered by a walking holiday or long weekend spent in flip flops or unsupportive sandals,” says Heather Smart, a podiatrist and the co-founder of ZeroSole.
The majority of the world wears sandals all the time and is used to the lack of cushioning and flatter sole. In the UK we spend most of our time in closed-toe shoes. Switching between the two types can cause problems, as our feet aren’t used to the different muscle activation and forces through the foot that sandals have.
In particular, flip flops and sliders can cause tension in the tendons on the toes as you strain to keep them on your feet. 
If you’re just wearing that suboptimal shoe to go down to the pool or to put the bins out, that’s not a problem, says Branthwaite. “The issue is when people try to wear a style of sandal their gait pattern isn’t used to for a long period of time, increasing the forces around the limb.” 
If your foot isn’t strong enough to adapt to the change in its environment, this can put the foot under excessive strain forces and lead to pathologies such as tendinopathies and heel pain.
It’s not the only way our choice can have a ripple effect on our body. The Telegraph’s news editor Caroline Argyropulo-Palmer’s father suffered from lockjaw as a result of wearing sandals with no heel strap. “He was waking up each morning unable to fully open his mouth, with this lasting most of the day. He went to the dentist about it thinking it was caused by his teeth somehow, and they said it was because he was clenching his jaw in his sleep and told him not to sleep on his back anymore. But that made no difference. 
“Then someone who did reflexology told him it was his shoes (he was wearing an old pair of walking sandals). He bought a new pair and the lock jaw stopped.”
Branthwaite explains how restriction in your usual movement pattern due to rigidity in the ankle can cause you to push your head forward to propel your body weight forward. 
“That would put strain on the two joints that connect your lower jaw to your skull and lead to it stiffening.” 
Wearing a sandal that restricts our ability to walk in our normal way also increases the risk of an unexpected fall. “Styles of footwear that reduce the range of movement in the ankle mean that you tend to shuffle more leading to trips.”
Changing our shoe style changes our centre of mass, as well as the way that we use our feet, which can cause a chain reaction further up our body. 
For example, people who have lower back pain may find that pain increases if they wear very flat shoes. It’s because of the natural curve, aka lordosis, of the spine, explains Branthwaite: “If you’ve not got enough ankle range of movement to be able to get your foot down flat then your pelvis will tilt accordingly to make you stand up right.”
However if you elevate your heel and move your centre of mass anteriorly, aka forward, this enables the spine to sit more upright. “In people that have lower back pain that reduces the activity of the spinal muscles.”
You might see someone shuffling along in sliders, struggling to keep them on, and on the other side of the street, someone else is marching away happily in the same pair of flimsy footwear. That’s because gait is very specific to the individual. 
“If the second person has enough strength and function in their feet then they will be OK,” says Branthwaite. 
She sees patients who live in Birkenstocks and can’t wear anything else because they constantly wear them. The extremely flat style may also suit those with lower arches. 
However some people’s anatomy favours a higher heel incline; for example if you have a high foot-arch, a 1cm to 2cm ramp can be more comfortable.
If you want a good all-rounder, Smart recommends Teva style sandals over flip flops: “As they offer numerous fastenings and well-structured soles. If you require further support, such as for over-pronation, Vionic sandals are a perfect choice.”
In general, younger people tend to be more adaptable to different types of footwear. That’s because as we age our joints become stiffer and weaker. 
“Once you pass 40 the muscle protein fibres change, and connective and collagenous tissues start to alter. Then the type of shoe we choose can become more of a problem,” says Branthwaite. 
Unless you invest in foot health to stay as strong as you’ve always been, then a loss of muscle mass will mean a loss of function.
While you can develop plantar fasciitis at any age, it is most common in people between the ages of 40 and 60, due to ageing ligaments that break down and lose elasticity over time.
An underexplored area of research, says Branthwaite, is the effect of the menopause. 
“The physical change that happens around the menopause and the hormonal changes mean that there is an impact on the connective tissues throughout our body.”
Have you ever wondered why men struggle to walk, let alone run for a bus, in high heels? It’s not because women are predisposed to be better in them, but because men simply are not used to wearing them. 
“The people who adapt best to different styles of shoe are those who have a high level of variance in the shoes that they wear day to day,” says Branthwaite. 
So if you wear trainers all day, every day then you’re only going to be able to wear trainers “because you’ve become so adapted to that scenario,” she explains.  
“You wouldn’t just launch into a marathon without the proper training. It’s the same when we switch to summer sandals suddenly.”
Invest in strengthening your feet. Do things like standing on one leg, raise your heels so that you lift onto the ball of your foot. Wiggle your toes. Try picking a sock up off the floor. “These are all simple things that keep your feet strong,” says Branthwaite. 
A rule of summer sandal thumb is to choose the footwear for the activity you are doing. “That will minimise any strain on the foot and reduce the risk of injury,” says Branthwaite. If you are off to a summer barbecue and all you are doing is getting out of the car, walking into a back garden and sitting down, then you can opt for the thin leather-soled thong with jewels on the front. A hike in the same sandals will cause prolonged force on the body as you heel strike, making periostitis, aka a bruise of the heel bone, more likely. 
“That’s a common injury when people wear footwear with no cushioning,” she says. Instead choose a walking sandal that’s got straps and fasteners on and has a sole like a trainer.
Lots of sandals today are made out of high shock absorbency materials used to make trainer soles. Over time and use though, the foam will become compressed. The cellular structure of the foam changes and becomes stiffer and harder. You may have noticed this with an old pair of flip flops. 
If you continue to wear them then the material now behaves and becomes more like that of a thin leather sole. “We know from research that wearing a worn shoe significantly alters the forces and the way the joints move,” says Branthwaite. This will increase the likelihood of a foot injury. 
If the tread on your shoe becomes too worn then you are also more likely to slip and fall. Equally, the same can be said for new leather sandals. 
“Make sure to scuff the bottoms of new leather sandals to make them more grippy,” says Branthwaite. Ultimately what sandal you wear is about how frequently you wear them and what you’re doing in them. “Those are the key factors to consider when you’re making any footwear choice,” says Branthwaite.
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