Asked to imagine someone ‘strong’ and perhaps you’d conjure up an image of Arnold Schwarzenegger in his weightlifting heyday, all gleaming biceps and pecs. The world’s fastest man, Olympic running legend Usain Bolt, might also come to mind.

But what if we chose different qualities to define strength rather than merely the ability to lift heavy things briefly or move fast for a short period of time?

Instead, what if we defined strength by gritty endurance, astonishing biological complexity or muscle durability? Or what about the capacity to fight off illnesses as well as toughness in the face of pain?

You might be surprised to hear there is one sex that’s the runaway winner in these categories of strength – and it’s not men.

After interviewing a raft of experts and decoding the latest science about strength for my new book on the female body, I am firmly convinced women have been erroneously labelled as the weaker sex for too long.

Indeed, as I reveal here, so much of the latest research firmly indicates the opposite…

WOMEN’S MUSCLES HAVE MORE STAYING POWER

Physical strength has always been defined by what men’s bodies can do best: usually a variation on lifting, pushing, pulling or flinging the heaviest weight one can manage in a single effort or contraction.

By contrast, lifting a weight over many repetitions – also known as endurance – simply isn’t how most people understand strength.

When using a weight at up to 80 per cent of the maximum a person could lift, several studies have  found women could do more reps than men

Satrre Vartan is a science and environment writer, with a strong focus on women’s bodies and their connection to the natural world

Professor Sandra Hunter found that women could endure holding weights much longer than men during a study in the 1990s

Yes, male arm muscles can be twice as strong for quick, heavy lifts – thanks, in part, to men having more muscle fibres in their arms – but muscles need to do more than just lifting or chucking something weighty a few times.

Scientists have found that women’s muscles can beat men in terms of endurance, whether it’s repeatedly lifting a weight or maintaining physical activity for long periods.

I spoke to Professor Sandra Hunter, an expert in exercise physiology at the University of Michigan, who uses the term ‘fatigability’ to describe how quickly muscles tire.

In the 1990s, she conducted a study examining how long both sexes could perform an isometric (or sustained) muscle contraction – such as standing and holding a bag of shopping. She tested herself first, using a chair with sensors that measured how hard someone could push upward at a certain force and for how long.

Professor Hunter knew the maximum weight she could lift from that position, then set the machine at 20 per cent of that maximum. She found she could hold her weight for 30 minutes.

A female student beat her, holding her weight for an hour.

Then Professor Hunter tested a burly male student, who had a maximum weightlifting power about seven times hers. Again, she set his test weight at 20 per cent of his maximum.

‘After about a minute, I realised he was going to fail really quickly,’ she told me. ‘He lasted about two minutes – and he was not the only man to have this issue.’

In the study, published in the Journal of Neurophysiology, Professor Hunter reported women sustained the isometric muscular contractions for twice as long as men, even at the same relative intensity.

She thought this might be because of body mechanics: in larger muscles, blood flow can become blocked when held in position. When muscles don’t get enough oxygen, they fail – meaning the burlier a person is, regardless of gender, the more likely their blood flow might be blocked when a muscle is contracted.

She then did another test to combat this effect, where the study participants contracted their arm muscle, held it for six seconds, and then released for four seconds. The weight was set at 50 per cent of their maximum.

Even in this tweaked study, she found women lasted twice as long as the men. This proved, in terms of sustained muscular work, that ‘women on average have more fatigue-resistant muscles than men’, she said.

In 2023, a major review of studies, published in the Journal of Strength and Conditioning Research, agreed. When using a weight at up to 80 per cent of the maximum a person could lift, many of the studies found women could do more reps than men.

One potential answer for why women’s muscles persist is because women’s muscles burn more fat and fewer carbohydrates. This means they have superior long-term strength. While in the short term, burning carbs gives men’s muscles a boost, in longer-duration exercise they’ll burn out faster than women.

A TURBO-CHARGED IMMUNITY

The differences in immunity between male and female bodies are significant and striking. The authors of one 2006 study published in the journal Human Nature on the causes of higher levels of early mortality in men concluded: ‘Being male is now the single largest demographic risk factor for early mortality in developed countries.’

In the UK, women live for about three years longer than men – which is echoed across the rest of the world, with three to seven-year gaps consistently reflected across various populations.

The immunity difference between male and females starts early. In neonatal intensive care units, more boys die than girls, and even among boys born on time, infant mortality is higher.

This has been explained by ‘sex differences in genetic and biological makeup, with boys being biologically weaker and more susceptible to diseases and premature death’, according to a 2012 paper by the University of Ottawa. And at every step along the way – from babyhood to old age – females out-survive males.

For instance, studies have repeatedly shown male bodies have almost double the risk of death from cancer. (Studies show that men both get more cancers and also die from cancer once they have it, more often than women.)

Other research, published in 2014 in the Journal of Infectious Diseases, reveals a male’s antibody response to flu vaccines is about half that of a woman’s, which helps explain why illness and death from flu in older men are more common.

According to the Mayo Clinic, female bodies clear pathogens of all types – including fungi, parasites, bacteria, and viruses – more quickly and effectively, and they show stronger responses to most vaccines.

Part of this is down to women having two X chromosomes, whereas men just have one. Think of it this way: if you have two versions of a gene carried on the X chromosome (not just one, as a man has), it means XX carriers have two sets of every kind of immune cell.

This means the two genes can sometimes compete to produce the strongest version of a given immune cell. In other cases, it means there is a greater variety of cells to fight a particular pathogen.

Women have other advantages, too. Up to 80 per cent of all white blood cells are neutrophils, which constantly circulate looking for invaders. Females average a higher number of neutrophils compared with men. Not only that, their neutrophils are smarter and stronger.

Research published as part of a US government study in 2020 found neutrophils in female blood were more mature, giving them full capacity to fight infections, and more responsive than those in male blood.

Women also have more macrophages – cellular soldiers that eliminate infectious agents.

And to top it all off, their B cells – immune cells that create specific antibodies to eliminate an invading virus – go through more cycles of mutations than men, producing antibodies that are better fighters.

WOMEN CAN OUTLIVE MEN IN FAMINES

Research also shows even an average female body can reach the athletic heights you might imagine were only reserved for male athletes.

Academics at Duke University discovered this when analysing the ultimate limit of human endurance in 2019. Recruiting subjects from the Race Across America – which starts at the Pacific Ocean and ends at the Atlantic, taking some five months to run, 25 miles a day, six days a week – they tracked their maximum metabolic rate, which is the rate your body converts food and drink into physical energy.

Researchers took the results from the three men who finished the race, and added it to data from other, shorter endurance competitions, like the Tour de France.

They found even among these very athletic individuals there’s a metabolic limit as to how far a body can be pushed in endurance events: around 2.5 times the body’s resting metabolic rate.

Fascinatingly, aside from these extreme athletes, there’s another group whose metabolic limits get close to that 2.5 number, 24/7, for months at a time: pregnant women.

This proves the female form is literally built for stresses comparable to these ultra-endurance events. After all, growing a foetus from scratch requires tremendous energy, grit and physical power.

Such endurance is seen again, in a 2018 research paper, which showed that throughout history, women were more likely to survive a wide variety of long-term bodily stresses, including famines and epidemics. As a species, we wouldn’t have survived without women’s endurance.

PERIODS ARE A SUPER STRENGTH

Every time a woman has a period, some wounding occurs on the uterus’s interior walls. Immune cells assist in healing the uterus, and a week later, you’d never know there was any damage to it. It heals without scarring every time, up to 500 times in a woman’s life.

Australian researchers investigating this ‘unique, rapid-repair environment’ have identified nearly 200 proteins that were found in higher quantities in menstrual blood, compared to blood in other parts of the body. These proteins were antimicrobials and antioxidants.

Period blood also contains specialised cells, mesenchymal stem cells, which can convert into fat cells, bone cells and cartilage.

I interviewed world-renowned Professor Caroline Gargett of Monash University, who is currently incorporating these cells into a degradable mesh for treating pelvic organ prolapse, making the implant more compatible with the body.

Other scientists are researching mesenchymal stem cells’ potential in wound healing, or treating liver disease and Alzheimer’s. A woman’s period could hold the key to healing potentially fatal illnesses for both sexes.

PUSHING THROUGH THE PAIN WITHOUT RELIEF

I’ve always been struck by the irony that women are meant to be the ‘weaker sex’, yet it’s ‘normal’ for us to endure pain without medical relief, whether it be from periods, childbirth or procedures such as inserting IUDs. Meanwhile, there are videos online of men crying out in agony when they are subjected to the equivalent pain of menstrual cramps via electric stimulation. Certain aspects of a woman’s biology make it more likely that she will experience pain.

For example, when oestrogen levels are low over the course of a menstrual cycle, females experience more pain.

As well as this, luteinising hormone, which tells the ovaries to release an egg, also seems to make opioid painkillers less effective by desensitising receptors for opiates in the brain, making you feel more pain. While experiencing pain is not pleasant, more practice with pain makes any body better at handling it (that goes for athletes of both sexes, as well as women).

Given all this, it’s perhaps not surprising that a 2019 study by McGill University showed men and women recall pain differently.

Participants were subjected to a painful experience in a lab setting before returning the next day, knowing it would be repeated.

Men were found to be more stressed by, sensitive about and reactive to the anticipation of future pain. As a result, they rated the repeated pain experience as more intense than women did.

Dr Jeffrey Mogil, a neuroscientist and co-author of the paper, said: ‘One thing is for sure, after running this study, I’m not very proud of my gender.’

Adapted from The Stronger Sex by Starre Vartan (Atlantic Books, £22), to be published 24 July. © Starre Vartan 2025. To order a copy for £19.80 (Offer valid to 29/07/25; UK P&P free on orders over £25) go to mailshop.co.uk/books or call 020 3176 2937.