Women are, on average, substantially less strong than men in absolute terms, with the gap more pronounced in the upper body than the lower body. A widely cited laboratory study found that women produced roughly 52% of men’s upper-body strength and about 66% of men’s lower-body strength, with the difference largely tied to how lean tissue is distributed across the body.1PubMed. Gender differences in strength and muscle fiber characteristics But “the strength gap” is not a single number, and the story gets considerably more interesting once you move past the headline comparison.
The Upper Body Versus Lower Body Split
The gap between men and women is not uniform across the body. In nearly every study that measures both, the upper body shows a larger disparity than the lower body. One reason is straightforward: women tend to carry a smaller share of their total lean tissue in the chest, shoulders, and arms compared to men. A study of university students found that women’s overall strength corresponded to just over 50% of men’s, closely tracking the fact that women had about 55% of men’s lean mass.2PubMed Central. Sex differences in upper and lower strength and their association with body composition among university students In the lower body, where women’s lean mass distribution is closer to men’s, the strength ratio narrows. This anatomical split matters for practical contexts: a woman may be comparatively closer to a man’s capacity in tasks that load the legs and hips than in tasks that demand pressing or pulling with the arms.
Muscle Mass Does Not Explain Everything
An intuitive assumption is that if you account for the difference in muscle size, the strength gap would vanish. It does not. Research comparing male and female athletes found that even after adjusting for the thickness of the specific muscles being tested and for overall lean body mass, men still produced significantly greater force and power outputs.3PubMed Central. A Comparison between Male and Female Athletes in Relative Strength and Power Performances Part of the explanation lies deeper, in the architecture of the muscle fibers themselves.
A meta-analysis of skeletal muscle fiber types found that men have larger cross-sectional areas across all fiber types, but the difference is especially pronounced in Type II fibers, the fast-twitch fibers responsible for explosive, high-force contractions. Men also have a greater proportion and area percentage of Type II fibers, while women tend to have a higher proportion of Type I fibers, the slow-twitch variety associated with sustained, lower-intensity effort.4PubMed. Sex differences in skeletal muscle fiber types: A meta-analysis This is not a trivial distinction. Because Type II fibers generate more force per unit of area than Type I fibers, equal-sized muscles with different fiber-type compositions will produce different peak forces. A narrative review synthesizing the literature concluded that men’s greater strength comes not from higher voluntary activation of their muscles, as was once speculated, but from their greater total muscle mass and larger Type II fiber areas.5PubMed. Narrative Review of Sex Differences in Muscle Strength, Endurance, Activation, Size, Fiber Type, and Strength Training Participation Rates, Preferences, Motivations, Injuries, and Neuromuscular Adaptations
Testosterone and Muscle Growth
Testosterone is the hormone most directly linked to the strength gap, and its effects are dramatic. A landmark trial in the New England Journal of Medicine gave supraphysiologic doses of testosterone to healthy men and tracked what happened over ten weeks. Even the men who did not exercise at all gained meaningful muscle size and strength: their bench press went up by about 9 kg and their squat by about 16 kg, compared to essentially no change in the placebo group. Men who received testosterone and also trained saw the largest gains of all, with fat-free mass increasing by over 6 kg.6PubMed. The effects of supraphysiologic doses of testosterone on muscle size and strength in normal men Laboratory work has shown that testosterone drives muscle fiber growth through specific signaling pathways inside the cell, increasing the cross-sectional area of muscle tubes in culture.7The FASEB Journal. Testosterone induces skeletal muscle hypertrophy via Akt/mTOR/S6K1 pathway and the androgen receptor
Since men typically have about ten to twenty times the circulating testosterone of women, this single hormonal difference creates a persistent anabolic advantage from puberty onward. Estrogen, however, is not irrelevant. A growing body of evidence supports estrogen’s role in maintaining muscle mass, enhancing recovery from damage, and supporting connective tissue health, effects that become especially visible when postmenopausal women lose estrogen and experience accelerated muscle decline.8American Physiological Society (J Appl Physiol). Estrogen replacement and skeletal muscle: mechanisms and population health
Where Women Have the Advantage: Fatigue Resistance
The conversation shifts when you stop measuring peak force and start measuring how long someone can sustain effort. Women consistently show greater resistance to muscle fatigue in certain tasks, particularly in the upper body. In one study, women held a sustained elbow flexion contraction for an average of about 112 seconds, while men lasted only about 80 seconds, a large and statistically robust difference. Interestingly, the same study found no meaningful sex difference in fatigue for the ankle dorsiflexors, suggesting the advantage is muscle-group dependent rather than universal.9PubMed Central. Sex Differences in Fatigue Resistance Are Muscle Group Dependent
Why would women outlast men during sustained contractions? Part of the answer involves what happens in the brain during intense effort. When men performed maximal sustained contractions of the knee extensors, their force dropped by about 24%, while women’s dropped by only about 16%. The critical finding was that this difference tracked with “central” fatigue, meaning the nervous system’s reduced ability to fully drive the muscle, rather than with peripheral fatigue in the muscle itself. Men also showed a more pronounced “cross-over” effect, where fatiguing one leg reduced the force capacity of the opposite, unfatigued leg, again pointing to a brain-level mechanism.10Pflugers Archiv European Journal of Physiology. Central fatigue explains sex differences in muscle fatigue and contralateral cross-over effects of maximal contractions Women’s higher proportion of Type I muscle fibers likely contributes as well, since those fibers are inherently more fatigue-resistant.
Training Gains Are Remarkably Similar
One of the most persistent myths about women and strength training is that women cannot build muscle as effectively as men. The data say otherwise, at least in percentage terms. After ten weeks of a resistance training program targeting the elbow flexors, men and women improved their strength by almost identical percentages: about 11.6% for men and 11.8% for women.11PubMed Central. Comparison of upper body strength gains between men and women after 10 weeks of resistance training A longer and more comprehensive training study found a similar pattern. Both men and women significantly increased strength across four different exercises. In percentage terms, women actually had slightly higher gains in some tests, including elbow flexion (about 59% versus 36%) and knee flexion (about 24% versus 13%). Muscle hypertrophy was substantial in both sexes: upper-arm muscle cross-sectional area increased by about 16% in men and 23% in women.12PubMed. Muscle hypertrophy in men and women
The caveat is that men’s absolute gains were larger in some measures, because they started from a higher baseline. If a man begins a program bench-pressing 80 kg and a woman begins at 40 kg, and both improve by 30%, the man adds 24 kg while the woman adds 12 kg. The gap in absolute strength stays put, or can even widen, even as the rate of improvement is the same. This is why women can respond to strength training just as robustly as men in physiological terms while the absolute performance gap remains.
Rate of Force Development and Explosiveness
Peak strength and explosive power are different qualities. Peak strength is how much force you can produce; explosiveness is how quickly you can ramp that force up. Some research suggests the sex gap in rate of force development is smaller than the gap in peak strength. One study comparing men and women during countermovement jumps found no statistically significant difference in the rate at which they developed force, even though men produced higher absolute force.13Journal of Exercise Physiology Online. Gender similarities in rate of force development and time to takeoff during the countermovement jump Similarly, earlier work measuring the time required to reach 25%, 50%, 75%, and 100% of maximal voluntary contraction found similar times in men and women.14PubMed. Electro-mechanical response times and rate of force development in males and females In other words, both sexes appear to activate their available muscle at roughly the same speed, but men have more muscle to activate, which is why their absolute power output is still higher.
The Ultramarathon Puzzle
In short-distance running, from 100 meters to the marathon, men outperform women by roughly 7% to 14%. But something curious happens at extreme distances. A study that specifically examined ultramarathons where men and women participated in comparable numbers found that the performance gap shrank dramatically. In 50-mile races, the median finish time showed only a 1.2% difference between sexes, which was not statistically significant. In 100-mile races, the gap was about 3.2%, again not significant. Even among the top ten finishers, the gap in 100-mile races was only about 4.4%, much smaller than the double-digit gaps seen in shorter events.15Canadian Science Publishing (Appl Physiol Nutr Metab). Sex differences in ultramarathon performance in races with comparable numbers of males and females
This finding has fueled speculation that women may be physiologically suited for ultra-endurance events, possibly because of their greater reliance on fat metabolism, their higher proportion of fatigue-resistant Type I fibers, or their apparent advantage in pacing. The researchers noted that controlling for participation numbers was critical: in events with very few female entrants, the apparent gap may be inflated because the female field is thinner and less competitive. When participation is balanced, the gap nearly disappears at the longest distances.
Recovery After Hard Training
If men and women train with comparable relative intensity, do they recover at the same rate? The picture is mixed and somewhat surprising. One study found that women and men experienced similar levels of immediate strength loss after a resistance exercise session (about 24% and 27% drops, respectively), but men showed greater increases in markers of muscle swelling immediately after the workout and more soreness at 72 hours.16Isokinetics and Exercise Science. Men and women experience similar muscle damage after traditional resistance training protocol A different study looking at recovery over four days found the opposite pattern for strength restoration: women experienced a longer recovery timeline for peak torque, even though their delayed-onset muscle soreness followed a course similar to men’s.17PubMed. Dissociated time course of recovery between genders after resistance exercise The upshot is that “recovery” is not one thing. How sore you feel, how much swelling occurs, and how quickly your muscles regain their full force capacity can all follow different timelines in men and women. Neither sex has a clear blanket advantage.
Does the Menstrual Cycle Affect Strength?
This is a topic that generates enormous interest, and the honest answer is that the evidence is surprisingly inconclusive. A narrative review of the literature found that studies examining objective performance through anaerobic, aerobic, or strength tests do not report clear, consistent effects of menstrual cycle phase on physical performance.18PubMed Central. The Impact of Menstrual Cycle Phase on Athletes’ Performance: A Narrative Review A more recent study specifically looked at back squat performance and jump ability across different cycle phases and found no significant differences. However, it did detect an interesting wrinkle: higher-level athletes showed more variation in squat performance across their cycle than less experienced lifters, suggesting that cycle-based effects may only become detectable at elite performance levels where margins are tiny.19PubMed Central. The effect of the menstrual cycle phases on back squat performance, jumping ability and psychological state in women according to their level of performance -a randomized three-arm crossover study
For most women training at a recreational or intermediate level, the practical takeaway is that menstrual cycle phase is unlikely to meaningfully constrain a given workout, even if subjective feelings of readiness fluctuate.
Tendons and Biomechanics
Strength is not purely a muscle story. Tendons, the connective tissue cables that transmit muscle force to bone, also differ between the sexes. A study of Achilles tendon behavior during walking found that men had significantly larger tendon dimensions and greater tendon stiffness. Women, in contrast, showed greater peak tendon displacement and strain during the push-off phase of walking, while men had higher loading rates in late stance.20PubMed. Sex differences in Achilles tendon behaviour during walking More compliant tendons in women could affect how efficiently force is transmitted during both everyday movement and athletic performance. This is an area where the research is still developing, but the sex differences in connective tissue may also help explain why women have different injury patterns, particularly higher rates of certain ligament injuries.
Protein Synthesis Across the Lifespan
Here is a finding that surprises many people: women actually have a higher rate of muscle protein synthesis than men, and this holds across the lifespan. A study measuring whole-body protein synthesis per fat-free mass and muscle protein fractional synthesis rate found that both measures were higher in women than in men at every age studied. Both sexes showed declines with aging, but women consistently ran a higher baseline rate.21PubMed Central. Higher muscle protein synthesis in women than men across the lifespan, and failure of androgen administration to amend age-related decrements If women build protein faster, why are they still smaller and weaker? Because protein synthesis is only half the equation. Muscle size is determined by the balance between synthesis and breakdown, and testosterone shifts that balance powerfully in men’s favor by also suppressing breakdown and promoting net protein accretion on a larger frame.
The aging dimension adds another layer. Among community-dwelling older adults, women had a higher prevalence of sarcopenia, the age-related loss of muscle mass and function, at about 26% compared to about 19% in men.22PubMed Central. Gender-Specific Risk Factors and Prevalence for Sarcopenia among Community-Dwelling Young-Old Adults This might seem paradoxical given women’s higher protein synthesis rates, but it tracks with what happens when estrogen declines after menopause: the hormonal support for maintaining muscle deteriorates, and women’s already-lower muscle reserves leave them with less of a buffer before function starts to slip.
Load Carriage and Everyday Physical Tasks
Most of the research discussed so far comes from laboratory tests of maximal performance. But everyday physical work rarely demands a one-rep max. A study investigating load-carrying economy, how much extra energy it costs to haul a given load, found no sex differences when men and women carried the same weight relative to their body mass. Both sexes experienced the same proportional increase in energy cost above their unloaded walking cost.23PubMed. No sex differences in the economy of load-carriage The obvious difference is that men tend to be heavier and carry more absolute load, but the efficiency of the human locomotor system does not favor one sex over the other. For practical purposes, a woman carrying a backpack equal to 30% of her body weight is working just as efficiently as a man carrying 30% of his.
This finding is relevant to occupational settings and military contexts where load-carriage standards have historically been set in absolute terms. An absolute standard of, say, 30 kg penalizes a 60-kg woman far more than a 90-kg man, not because her muscles are less efficient, but because the load represents a much higher fraction of her capacity. Whether standards should be absolute or relative is a policy question, not a physiological one, but the physiology says the underlying machinery works the same way.
Voluntary Activation and the Neural Side
An older explanation for the strength gap proposed that women could not voluntarily activate their muscles as fully as men. Modern evidence has largely put this to rest. As noted earlier, a comprehensive review concluded that the gap is driven by muscle mass and fiber area, not by differences in neural drive.5PubMed. Narrative Review of Sex Differences in Muscle Strength, Endurance, Activation, Size, Fiber Type, and Strength Training Participation Rates, Preferences, Motivations, Injuries, and Neuromuscular Adaptations That said, some subtle differences exist. One study found that women showed less contralateral motor activity during maximal effort and a larger gap between the force their muscles could produce when electrically stimulated versus what they produced voluntarily, hinting that sex differences in voluntary activation may still matter in specific contexts, even if they are not the main story.24PubMed Central. Age- and Sex-Related Differences in Motor Performance During Sustained Maximal Voluntary Contraction of the First Dorsal Interosseous The practical upshot: if you are a woman who is new to heavy lifting, the initial strength gains you experience are mostly neural, your brain getting better at recruiting the muscle you already have, and those early neural gains proceed at the same rate as they do in men.