A girl can absolutely be stronger than a guy, and it happens all the time in everyday life. But population-level data tells a more complicated story: on average, males carry substantially more muscle mass and produce considerably more force, with the gap being largest in the upper body. The interesting part isn’t whether overlap exists between the sexes, because it clearly does, but how large or small that overlap is depending on what you measure, which muscle groups you test, and how training status factors in.
The Average Gap in Numbers
When researchers test large groups of men and women on standard strength measures, the differences are consistent and sizable. In a study of university students, women’s strength values corresponded to just over 50% of men’s, closely tracking a lean-mass difference of about 55%.1PubMed Central. Sex differences in upper and lower strength and their association with body composition among university students Another study of students found that men averaged about 44 kg on hand-grip strength while women averaged 31 kg, and for back squat the gap was even wider: roughly 141 kg versus 82 kg.2PubMed Central. The effect of body composition on strength and power in male and female students
The gap isn’t uniform across the body. Upper-body tasks show the widest difference. One classic anthropometric study found that the largest sex difference appeared in pulling strength, where women scored about 53% of male values. Hand-grip came in at about 59%, and vertical jump at about 66%.3PubMed. Anthropometry and strength relationship: male-female differences That pattern shows up again and again in the literature: the further you move from the legs toward the arms and shoulders, the wider the gap tends to get. Across multiple populations with varying nutrition levels, males average about 65% more total muscle mass than females and roughly 72% more arm muscle.4PubMed Central. Substantial but Misunderstood Human Sexual Dimorphism Results Mainly From Sexual Selection on Males and Natural Selection on Females
How the Distributions Actually Overlap
Averages can be misleading if you forget that every average sits atop a wide bell curve. The question most people really want answered is practical: how often does a specific woman’s strength exceed a specific man’s? The most cited data on this comes from a study that measured hand-grip strength in young men, young women, and highly trained female athletes. The average man squeezed with about 541 newtons of force, compared to about 329 newtons for the average woman. But the distributions told the real story: 90% of the women tested produced less grip force than 95% of the men.5PubMed. Hand-grip strength of young men, women and highly trained female athletes
That means roughly 10% of the women in the sample did overlap with the bottom portion of the male distribution. If you pulled a random woman and a random man off the street, the man would almost always have a stronger grip. But “almost always” is not “always,” and real life doesn’t deal in averages. Body size, training history, age, and genetics all shift where any individual falls on the curve.
International norms based on over 2.4 million adults across 69 countries confirm the general pattern. Peak grip strength occurs around age 30 to 39, averaging about 50 kg for men and about 30 kg for women. The decline with aging is somewhat steeper for men during middle adulthood.6PubMed. International norms for adult handgrip strength: A systematic review of data on 2.4 million adults aged 20 to 100+ years from 69 countries and regions So an active 35-year-old woman and a sedentary 70-year-old man might be in the same ballpark for grip strength, simply because aging eats into the male advantage over time.
Can a Trained Woman Beat an Untrained Man?
This is the version of the question people argue about most, and the evidence is surprisingly clear, if a bit deflating for the “just train harder” camp. A direct comparison of untrained men and trained women athletes found that the untrained men still had greater upper- and lower-body strength, both in absolute terms and when adjusted for body weight, height, and skeletal breadth.7PubMed Central. Strength comparisons in untrained men and trained women athletes The grip-strength study mentioned above reinforced this: even female national-level athletes, among the strongest women in their countries, averaged grip forces that only reached about the 25th percentile of the untrained male sample. Elite female athletes rarely surpassed the 50th percentile of untrained men.5PubMed. Hand-grip strength of young men, women and highly trained female athletes
That doesn’t mean training is pointless for women or that every man is stronger than every trained woman. It means that on grip-specific tasks, which heavily favor upper-body mass and forearm development, the male hormonal advantage is large enough that years of elite training can’t fully close the gap for most women. For lower-body strength, where the sex difference is smaller, the overlap between trained women and untrained men is likely larger, though fewer studies have quantified this as precisely.
Why the Gap Exists
The most obvious driver is testosterone. Men produce roughly ten to twenty times more of it, and testosterone directly stimulates the muscle-building cells (satellite cells) that repair and enlarge muscle fibers. In animal models, removing testosterone dramatically reduced the number and activity of these cells, and replacing it restored them, with treated muscle containing roughly an order of magnitude more satellite cells than untreated muscle.8PubMed. Testosterone mediates satellite cell activation in denervated rat levator ani muscle The same basic mechanism operates in humans: higher testosterone means more protein synthesis, larger fibers, and greater peak force.
But estrogen isn’t just along for the ride. It plays its own role in maintaining muscle mass and strength in women. Estrogen helps preserve muscle by reducing a form of programmed cell death in muscle fibers, and it influences the force-generating capacity of muscle through effects on key proteins.9PubMed Central. Aging of the musculoskeletal system: How the loss of estrogen impacts muscle strength It also improves muscle mass and strength and increases the collagen content of connective tissues.10PubMed Central. Effect of Estrogen on Musculoskeletal Performance and Injury Risk The practical proof shows up in menopause: when estrogen drops, women lose muscle at an accelerated rate. Hormone therapy can help maintain or recover some of that lost muscle and strength.11PubMed Central. Estrogen replacement and skeletal muscle: mechanisms and population health
Beyond hormones, there are structural differences in the muscle itself. A large meta-analysis of muscle fiber types found that men have bigger fibers across the board, and a higher proportion of the fast-twitch (Type II) fibers that generate explosive force. Women, conversely, have a higher proportion of slow-twitch (Type I) fibers, which are smaller but more fatigue-resistant.12PubMed. Sex differences in skeletal muscle fiber types: A meta-analysis This fiber-type difference partly explains why the strength gap is steeper for explosive tasks like throwing or jumping than for sustained efforts.
Pound for Pound, Is the Muscle Itself Weaker?
One common belief is that female muscle is inherently weaker, fiber for fiber. The evidence suggests otherwise. A foundational study measured the force produced per unit of muscle cross-sectional area and found that the ratio in men was 9.49 while in women it was 8.92, a difference that was not statistically meaningful.13PubMed Central. Strength and cross-sectional area of human skeletal muscle In other words, a square centimeter of muscle produces roughly the same force whether it belongs to a man or a woman. The sex difference in strength is driven overwhelmingly by how much muscle each person has, not by a fundamental quality gap in the tissue itself.
This is a useful corrective to the idea that women’s bodies are somehow built from inferior raw material. They aren’t. The difference is one of quantity, amplified by hormonal signals that favor more total muscle in males, and skewed toward the upper body where the size gap is largest.
Where Women Have a Physical Edge
Peak force is only one way to define strength. If you broaden the lens to include endurance under load, women show a measurable advantage in certain muscle groups. In a study comparing fatigue resistance during sustained contractions, women held the elbow-flexion task for about 112 seconds versus about 80 seconds for men, a large and statistically robust difference. For the ankle, however, there was no meaningful sex difference.14PubMed Central. Sex Differences in Fatigue Resistance Are Muscle Group Dependent
The mechanism behind this fatigue advantage appears to involve blood flow and neural drive rather than the muscle fibers themselves. When researchers clamped off blood supply to the working muscles using a pressure cuff, the sex difference in fatigue vanished entirely. That suggests women’s superior endurance may partly come from better blood delivery to working muscles during sustained effort, combined with more consistent neural drive; men showed a greater decline in their brain’s ability to fully activate the muscle during fatigue.15PubMed. Sex differences in human skeletal muscle fatigue are eliminated under ischemic conditions The higher proportion of slow-twitch fibers in women likely contributes as well, since those fibers are built for sustained work.
Women also tend to be more flexible. Muscle stiffness in the hamstrings and calves is consistently lower in women, and females outperform males in flexibility measures at all time points in stretching studies.16PubMed Central. Gender difference in effects of proprioceptive neuromuscular facilitation stretching on flexibility and stiffness of hamstring muscle While flexibility isn’t “strength” in the conventional sense, it matters enormously in sports like gymnastics, martial arts, and climbing, where the ability to produce force through a wide range of motion is the real performance bottleneck.
How Training Reshapes the Picture
Women respond to resistance training with the same fundamental adaptations men do: muscles grow, neural recruitment improves, and force output goes up. A recent review of the history and mechanisms of resistance training in women concluded that despite subtle physiological differences, women achieve measurable increases in strength, power, and athletic performance when they train with sufficient frequency, intensity, and duration.17PubMed Central. Evolution of resistance training in women: History and mechanisms for health and performance Women may also have unique advantages in areas like recovery and fatigue resistance that allow them to handle higher relative training volumes.
There’s an important distinction between relative gains and absolute outcomes, though. A woman who starts with a 60 kg squat and adds 40% after a training program now squats 84 kg. A man who starts at 120 kg and adds 30% now squats 156 kg. The woman made a larger percentage gain, but the absolute gap widened. This is why the trained-woman versus untrained-man comparison is so interesting: training can reverse the gap in some scenarios but rarely eliminates it for upper-body tasks, where the baseline difference is so large.
What the Sex Gap Looks Like During Adolescence
Before puberty, boys and girls are much closer in strength than most people assume. The gap widens sharply once sex hormones kick in. A study of adolescents found that differences in upper- and lower-body performance between boys and girls were only about 5 to 8% at age 12, but grew to 24 to 29% by ages 16 to 17.18PubMed. Effects of age and sex on field-based measures of muscle strength and power of the upper and lower body in adolescents The timing maps almost perfectly onto the surge in testosterone during male puberty, which drives rapid increases in muscle mass, bone density, and fiber size. Before that hormonal divergence, a strong 11-year-old girl can easily be stronger than many boys her age.
Tendons and the Hidden Infrastructure of Strength
Strength isn’t just about muscle. Tendons connect muscle to bone and transmit all of that force, and they respond differently to training depending on sex. A study of older adults found that 12 weeks of resistance training increased patellar tendon stiffness by about 80% in men but only about 13% in women.19PubMed Central. The magnitude and character of resistance-training-induced increase in tendon stiffness at old age is gender specific Women’s tendons also contain more water and less dry mass per unit weight than men’s, though the collagen content of the dry tissue is similar between sexes and is not altered by chronic resistance training.20PubMed Central. Impact of sex and chronic resistance training on human patellar tendon dry mass, collagen content, and collagen cross-linking
What this means practically is that tendons in men and women adapt to load through somewhat different pathways. A recent review concluded that the acute mechanical responses and longer-term adaptations of tendons to loading differ between sexes.21PubMed Central. Female Tendons are from Venus and Male Tendons are from Mars, But Does it Matter for Tendon Health? This has implications for injury risk and rehabilitation: training programs that work well for men’s tendons might not optimally load women’s, and vice versa. It’s a dimension of sex differences in physical performance that rarely makes it into casual conversations about who’s stronger.
What Hormone Therapy Reveals About the Testosterone Effect
Gender-affirming hormone therapy provides a kind of natural experiment for understanding how much of the strength gap is maintained by ongoing hormone levels versus permanently built into the body during development. A systematic review of these studies found that masculinizing hormone therapy (testosterone) increased muscle strength in most studies, while feminizing hormone therapy (estrogen plus testosterone suppression) decreased or left strength unchanged. Even after treatment, people assigned male at birth who underwent feminizing therapy still had higher absolute strength than people born female, but lower strength than men not on hormones.22PubMed Central. Muscle strength changes and physical activity during gender-affirming hormone therapy: A systematic review
A more detailed analysis found that in people undergoing feminizing therapy, fat mass increased by about 30% and muscle mass decreased by about 5% after one year, with a continued gradual decline beyond three years. By the two-year mark, running-based physical performance showed no advantage compared to women not on hormones. Push-up performance declined but still showed a residual advantage relative to women born female, suggesting that upper-body structural advantages from male puberty take longer to erode, if they ever fully do.23PubMed Central. The Impact of Gender-Affirming Hormone Therapy on Physical Performance These findings underscore that testosterone is the primary ongoing driver of the strength gap, but that skeletal frame size, bone structure, and years of prior muscle development also play lasting roles.
Mitochondria and the Energy Side of the Equation
Sex differences extend all the way down to the cellular power plants. A study comparing mitochondrial function in men’s and women’s skeletal muscle found that while the maximum capacity to produce energy was similar between sexes, women’s mitochondria were less sensitive to one of the key chemical signals that activates energy production during exercise. Women also showed greater sensitivity to a molecule that inhibits fat-burning within the mitochondria. The practical meaning is still being worked out, but these differences likely influence how men and women fuel their muscles during different types of exercise, which could relate to the fatigue-resistance advantages seen in women during sustained efforts.
None of these cellular differences make female muscle weaker per se. They represent a different metabolic tuning, one that may be optimized more for endurance and steady output than for short, explosive bursts. Whether that qualifies as “less strong” depends entirely on what kind of task you’re measuring and over what timeframe.