Females bodies are uniquely flexible—here’s why that makes them strong
From fat cells that stretch like spandex to more flexible muscles, scientists are finding that women’s bodies are just as strong as men’s.
On the slopes of Mount Kilimanjaro, the air thinned to a whisper, Deborah Clegg, a metabolic physiologist with a newfound appreciation for high places, found herself unfazed by the altitude. Her stride was steady, her energy unflagging. Clegg’s climbing partner, Biff Palmer—an accomplished nephrologist and mountaineer who had summited Everest and six of the world’s tallest peaks—found the climb more challenging.
Following their Kilamanjaro ascent in 2013, Clegg and Palmer continued scaling heights together, and they noticed a pattern. Mountain after mountain, Clegg consistently outperformed Palmer—not through bravado or better conditioning, they observed, but something deeper. Another factor seemed to be at play. Their conversations turned from competition to curiosity: why did her body seem so well adapted to the low-oxygen air and long exertion?
Back in the lab, they set out to answer that question.
By 2014, they found that estrogen appeared to protect against the physical stress of altitude by reducing hypoxia-inducible factor (HIF), a protein that helps the body adapt to lack of oxygen but causes inflammation and discomfort. More estrogen, the dominant hormone in female bodies, means less HIF and makes altitude easier to bear. That’s not the only advantage estrogen gave Clegg—it also plays central role in what’s known as metabolic flexibility—the body’s ability to shift between fuel sources, particularly from glucose to fat.
Clegg and Palmer’s finding is part of a growing body of scientific evidence challenging assumptions that women’s bodies aren’t as strong as men’s.
Science is increasingly showing that flexibility—the ability to adapt, shift, and recover across a lifetime—is one of the key strengths that makes female bodies so resilient. And there are three crucial ways that this trait makes women uniquely strong.
A more flexible metabolism
Clegg, now a professor of internal medicine at Texas Tech University Health Sciences Center, studies how estrogen and fat metabolism shape endurance.
Last Chance - Save up to $20!
Studies have shown that male bodies tend to rely more heavily on carbohydrates for short bursts of power, giving them an advantage in explosive strength, but female bodies do particularly well in endurance. Their bodies preferentially burn fat, which provides a steady source of energy. Fat as a long-burning, consistent fuel helped our female ancestors persist through long gestational cycles of pregnancy and breastfeeding while still hunting, gathering, and walking 8-10 miles a day.
Today, despite more fat stores, women deal with lower levels of metabolic disease—that’s by design.
“Women predominantly store fat in hips and thighs, which is a really beautiful safe space to store your fat because it's outside the abdominal cavity, where men store it inside,” she explains. Visceral fat around organs in the stomach area has more negative health impacts than fat stored subcutaneously, like female bodies tend to. The fat cells are different too.
“Our research has shown that the female fat cell is completely different than the male fat cell. The female fat cell is like spandex—it can stretch, taking up all the excess fatty acids and calories and storing it in a really healthy way,” says Clegg.
Male fat cells lack this capacity, and that difference is more than aesthetic.
Fat cells become inflamed and fibrotic when overloaded, increasing the risk of diabetes and cardiovascular disease. Women’s flexible fat cells, on the other hand, can more easily expand and contract through the demands of life—pregnancy, weight fluctuation, and endurance exercise. This expandability in the fat cells is “directly related” to sex hormones, says Clegg.
When it comes to sustaining energy over long periods, it’s “more beneficial to be a female than it is to be a male,” Clegg says. “The ability to flip between the two different energy substrates, glucose and fatty acids, also gives you a survival and a health benefit.”
The advantage isn’t just in mountain climbing: female bodies’ metabolic flexibility lowers the risk of cancer, diabetes, and metabolic syndrome—until menopause, when that flexibility wanes.
Bendier bodies
If metabolism shows the invisible side of adaptability, movement shows the visible one.
The human body has three kinds of physical flexibility, says Miho Tanaka, a physician who treats athletes from the New England Revolution soccer team and the Boston Ballet, and a sports medicine surgeon at Mass General Brigham. There’s functional flexibility—“like dancers, who are able to get into the splits”—muscular flexibility, which depends on how compliant certain muscles are, and joint flexibility, or what clinicians call laxity.
This flexibility is associated with more muscular efficiency and greater strength regardless of sex, which is why athletes incorporate it into their training. “Flexibility and having the ability to use the full motion of your joints is important in optimizing joint biomechanics. It directly influences how an athlete generates force,” says Tanaka.
On the flip side, “inflexibility often is a response to losing strength at end ranges of motion,” says Sophia Nimphius, pro-vice-chancellor of Sport at Edith Cowan University in Australia. In general, female bodies have greater muscular elasticity and range of motion in their joints. That’s likely because they have more estrogen, which increases collagen in connective tissues—a natural advantage that hasn’t been well-researched yet.
Physical flexibility also keeps bodies safer when exerting strength.
“Studies show that the more flexible your muscles are, the less likely you are to sustain a muscle injury or strain,” Tanaka says. But that balance is delicate. “If you have too much laxity, then you’re more prone to having joint injuries. It's really a fine line between having enough flexibility and having too much laxity.”
That fine line is one theory explaining why women are four to eight times more likely than men to suffer non-contact knee injuries. “Asymmetries in flexibility and muscle imbalances can put you at increased risk.”
However, another theory suggests women are more likely to experience these injuries because they have less training and support. “If laxity were primarily a sex-based mechanism, we would expect injury differences to be consistent across sports—but they aren’t,” says Nimphius.
Research has shown that in downhill skiing, where training is individual and starts young, there is no sex-based difference in injury rates.
That’s why research and training specific to female bodies is so important. Only six percent of sports medicine studies focus on women exclusively, and it’s well-known in sport science that for too long, women have been trained as smaller men rather than based on their own physical strengths.
Future training regiments that adapt to an athlete’s specific needs have the potential to reduce injuries (as some studies have already shown). Tanaka points to the potential of AI and machine learning to analyze large amounts of data that will allow doctors like her to “predict injuries and customize training plans accordingly.”
Adapting to major changes throughout life
Beyond metabolism and motion lies perhaps the most astonishing flexibility of all: the female body’s ability to undergo dramatic changes.
From first period to menopause, and through pregnancy, birth, and recovery, women’s systems repeatedly reconfigure—circulatory, immune, and musculoskeletal—without breaking down.
These physiological changes might even have advantages. Recent research has shown that breastfeeding may reduce breast cancer risk due to immune-cell recruitment into the breast. There’s also some evidence that some female athletes return to their sport even stronger after pregnancy and childbirth, matching or exceeding their pre-pregnancy abilities.
Adaptation, in fact, is the through-line. Across all scales—from mitochondria to muscle fiber to hormone cycle—the female body’s unsung power lies in its ability to bend without breaking.
For Clegg, the lesson crystallized halfway up a mountain; she was stronger because of her female body, not in spite of it.
The traits of the female body once dismissed as liabilities—fat storage, hormonal fluctuation, sensitivity—may in fact be the foundation of human survival.
Starre Vartan is the author of The Stronger Sex: What Science Tells Us About the Power of the Female Body, on shelves now.
