If 10-year-old Naomi Kutin wasn't the strongest girl in the world in 2012, then she'd be among the brawniest. That year, at a weightlifting meet in Corpus Christi, Texas, the 99-pound (44.9-kilogram) Kutin deadlifted a staggering 209.4 pounds (94.9 kilograms) and squatted slightly less [source: Zeveloff]. To put that Herculean feat into perspective, the New Jersey elementary schooler successfully squatted around 215 percent of her body weight -- the same body weight percentage a 180-pound (81.6-kilogram) adult man could likely squat [source: Cross Fit].
Her young age aside, Kutin's accomplishment was twice as significant considering her female physiology. Gender differences in athletic performance have narrowed over the past century as more sports have opened up to women and more attention and funding have been directed toward female athletic training through initiatives such as the Title IX law in the United States. But certain fundamental sex differences exist between men's and women's physical prowess. Men's greater upper body strength is a prime example. So while Naomi Kutin may be able to handily out-lift all her male classmates, she's an impressively strong exception to the rule.
Women's lower body strength tends to be more closely matched to men's, while their upper body strength is often just half that of men's upper body strength. In a 1993 study exploring gender differences in muscle makeup, female participants exhibited 52 percent of men's upper body strength, which the researchers partially attributed to their smaller muscles and a higher concentration of fatty tissues in the top half of the female body [source: Miller et al]. Another study published in 1999 similarly found women had 40 percent less upper body skeletal muscle [source: Janssen]. Even controlling for athletic aptitude doesn't tip the upper body strength scales in favor of the female; an experiment comparing the hand grip strength of non-athletic male participants versus elite women athletes still revealed a muscle power disparity in favor of the menfolk [source: Leyk et al].
Acknowledging this gender difference doesn't imply that weight-lifting women can't combat this bit of biological determinism and beef up their biceps; instead, men simply have a head start in that department thanks to their elevated levels of testosterone. The sex hormone has anabolic effects, meaning it promotes muscle development. Secreted by the pituitary gland, testosterone binds to skeletal fiber cells and stimulates the growth of proteins, the building blocks of meaty muscles [source: Roundy]. At the same time, however, testosterone also may shave off men's strength for the long haul.
Do women have more endurance than men?
For a glaring manifestation of biological sex differences in strength, look no farther than the pull-up. The process of hoisting oneself eye-level with an overhead bar is no big deal to plenty of men. Not so, however, for women. In fact, Marines require male recruits to complete at least three chin-ups in order to pass their physical entrance exam, while female hopefuls aren't asked to execute a single one [source: Parker-Pope]. That isn't letting military women off the hook easily; the female body simply isn't optimally built -- what with weight distribution and less testosterone-fueled muscle mass -- for the exercise.
The short bursts of energy required for weight lifting might not be the forte of the female body, but as more women have begun participating in endurance sports, such as running marathons, conflicting research has prompted a debate over whether they're better tailored for the long haul than men. The fastest male runners are swifter than the fastest female runners due to innate factors including muscle mass, higher oxygen intake and lower resting heart rates. That said, some studies have indicated that in ultradistance running -- beyond 30 miles (48 kilometers) -- the fattier female body can keep moving more efficiently than the muscular male frame since the fat represents more lasting, slower-burning energy stores [source: Maharam]. Estrogen may also offer an advantage of protecting against muscle fatigue, although its effects can vary by athlete and running conditions [source: Crowther]. Those biological benefits may help explain women's sudden surge in Iditarod races, the grueling Alaskan dog sledding competition, bringing home championships four years straight from 1985 through 1988 [source: Library of Congress].
Meanwhile, what isn't up for argument is that on average, women win at the ultimate endurance competition: life. Even as public health improvements have increased lifespans around the world, women still tend to live longer than men by five or six years [source: Kirkwood]. Evolutionary biology points to women's responsibility as child bearers for why the female body ultimately may be more resilient, having evolved heartier healing capacities on a cellular level [source: Dillner]. Another explanation for that consistent gender gap circles back to testosterone, the hormonal culprit behind gender unequal upper body strength. In addition to being anabolic (muscle-building), testosterone also is characterized as androgenic (or masculinizing), which can take the form of men indulging in riskier behaviors that could eventually curb their life expectancies. Not that it has to signal an early death sentence for men; by keeping those muscular bodies in shape, courtesy of testosterone, they can possibly ward off its more deleterious effects.
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Author's Note: Do men really have more upper body strength than women?
I'll admit that I'm not going to be breaking through any glass ceiling in the weight lifting department anytime soon -- or ever, to be honest. I have a textbook case of female physiology with a decent amount of lower body strength (at least that's what I tell myself) and little-to-no upper body strength to speak of. Despite regularly exercising, I've never successfully completed a single pull-up my entire life. Now, thanks to my research for this article investigating the gender differences in muscle mass and distribution, I can mentally surrender to the hormonal fact that push-ups, pull-ups and even monkey bar crossings will never be in my physical wheelhouse because I simply don't have the testosterone for it. Good thing I prefer jogging anyway.
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