Women demonstrate measurably greater endurance than men in several specific contexts, from resisting muscular fatigue during sustained contractions to maintaining more even pace in long races. Yet men still finish faster than women at virtually every competitive distance, from the 100-meter dash through ultramarathons of thousands of miles. The honest answer is that “endurance” is not a single trait, and the question splits into very different answers depending on whether you are talking about a muscle holding a contraction, a body completing a 26-mile marathon, or a swimmer crossing an open-water channel. The places where women pull ahead, and the reasons behind them, are more interesting than a simple yes or no.
Fatigue Resistance at the Muscle Level
When researchers measure how long a muscle can sustain a contraction before giving out, women consistently outlast men. This holds across a range of contraction intensities, from near-maximal efforts down to lighter sustained holds. Women demonstrate greater fatigue resistance during contractions performed at intensities relative to their own maximum force, and this advantage appears both above and below the metabolic threshold where muscles shift from aerobic to anaerobic energy supply.1PubMed. Sex differences in fatigability and recovery relative to the intensity-duration relationship
The advantage is not uniform across every muscle group, though. In one well-designed study, women held a sustained elbow flexion contraction for about 112 seconds compared to about 80 seconds for men, a large and statistically robust difference. But when the same subjects performed a similar task with ankle muscles, the gap disappeared: women lasted roughly 141 seconds and men about 129, a difference too small to be meaningful.2PubMed Central. Sex Differences in Fatigue Resistance Are Muscle Group Dependent The takeaway is that women’s fatigue advantage is real but depends on which muscles are being tested and under what conditions.
Part of the explanation lies in muscle composition. A large meta-analysis pooling data from men and women found that women have a greater proportion of slow-twitch (Type I) muscle fibers, which are the fibers best suited for sustained, low-intensity work. Women also had a higher ratio of slow-twitch to fast-twitch fiber area, meaning slow-twitch fibers occupied a bigger share of total muscle cross-section.3PubMed. Sex differences in skeletal muscle fiber types: A meta-analysis Separate research confirms that slow-twitch fiber percentage is higher in female non-athletes compared to male non-athletes, suggesting the difference is not just a training artifact.4PubMed Central. Association of muscle fiber composition with health and exercise-related traits in athletes and untrained subjects Slow-twitch fibers resist fatigue better than fast-twitch fibers, so having proportionally more of them is a structural advantage for endurance tasks.
Ultramarathon Performance and the Participation Problem
A claim that circulates widely in running culture is that women are “built for” ultramarathons, and that as race distances grow, women close the gap with men or even surpass them. There is a kernel of truth here, but the full picture is more complicated. In standard road races from 100 meters through the marathon, men outperform women by roughly 7% to 14%. In ultramarathons, that gap often appears much smaller, sometimes dropping to just a few percent.5PubMed. Sex differences in ultramarathon performance in races with comparable numbers of males and females
But a major confounding factor clouds the picture: participation rates. Most ultramarathon fields skew heavily male, meaning the pool of competing men is far deeper. When researchers examined only those ultramarathon events where men and women competed in roughly equal numbers, the performance gap shrank to about 1% to 3%.5PubMed. Sex differences in ultramarathon performance in races with comparable numbers of males and females That is a genuinely small gap, but it still favors men on average. The shrinking is partly explained by the statistical reality that when far fewer women enter a race, the chance that a world-class female talent shows up on any given race day is lower.
At extremely long distances, the picture shifts back toward men more clearly. An analysis of race results across distances from 50 miles to 3,100 miles found that the fastest men were roughly 17% to 20% faster than the fastest women at every distance examined.6PubMed Central. Performance differences between sexes in 50-mile to 3,100-mile ultramarathons Those events had overwhelmingly male fields, which inflates the gap compared to the balanced-participation analysis above. Still, even at enormous distances, women were not overtaking men at the elite level. The appealing narrative that women become the superior endurance sex if the race is long enough does not hold up to the data so far, though the gap is genuinely smaller in ultra-events than in shorter races.
Open-Water Swimming as a Revealing Case
If there is a sport where women have come closest to matching or beating men in endurance competition, it is open-water ultra-distance swimming. In the Manhattan Island Marathon Swim, the race record belongs to a woman: Shelley Taylor-Smith completed the course in 345 minutes in 1995, about 14% faster than the men’s record of 402 minutes set in 1985. Among the ten fastest performances ever recorded in that event, women were significantly faster than men.7International Journal of Sports Physiology and Performance. Women Outperform Men in Ultra-Distance Swimming – The ‘Manhattan Island Marathon Swim’ From 1983 to 2013
A similar pattern has unfolded in the Capri-to-Naples marathon swim, one of the oldest open-water races in the world. Over roughly six decades, the performance gap between the fastest men and women shrank from about 39% down to around 5% to 6%, a steady linear trend that led the study’s authors to speculate women might eventually match men’s times in that particular event.8PubMed Central. Will women soon outperform men in open-water ultra-distance swimming in the ‘Maratona del Golfo Capri-Napoli’?
Why swimming and not running? The most commonly cited explanation involves body composition. Women typically carry a higher percentage of body fat, distributed more peripherally. In cold open water, that extra insulation reduces heat loss and increases buoyancy, both of which become more valuable the longer the swim takes. In running, extra mass is a metabolic cost. In cold-water swimming, it is a thermal and mechanical asset. The sport-specific advantage here is not about endurance physiology in a general sense but about how the female body interacts with a specific environment.
Why Men Still Hold Most Speed Records
For all the areas where women show endurance advantages, men dominate finish times at almost every competitive distance. The primary reasons are cardiovascular and respiratory, and the differences are large.
Men have larger hearts relative to body size, which translates into a higher maximal oxygen uptake, the ceiling of aerobic capacity. Research has found that the difference in left ventricular mass between men and women accounts for about two-thirds of the sex gap in maximal oxygen uptake, with other body-size differences explaining nearly all the rest.9PubMed. Relationship of cardiac size to maximal oxygen uptake and body size in men and women Men also have higher hemoglobin concentrations, meaning each liter of blood carries more oxygen. Together, these factors give men a fundamentally higher aerobic ceiling, which matters whenever speed is the goal.
Women also face a respiratory disadvantage during intense exercise. Compared to men, women have smaller lungs and narrower airways relative to body size, which forces them to work harder to move the same volume of air. At high ventilation rates, women’s work of breathing can be roughly double that of men.10PubMed Central. Respiratory mechanics during exercise in endurance-trained men and women The extra effort is almost entirely due to higher airflow resistance in smaller airways, not differences in how elastic the lungs are.11PubMed. Sex differences in the resistive and elastic work of breathing during exercise in endurance-trained athletes Even when men and women are matched for lung size, the sex difference persists, suggesting it stems from genuinely smaller airway diameters in women rather than simply from having smaller lungs overall.12PubMed Central. Sex differences in the work of breathing during exercise are independent of forced vital capacity in healthy adults
The practical consequence is that at high exercise intensities, women are spending more energy just breathing, which diverts resources from the working muscles. This matters less in moderate, sustained efforts, where ventilation demands are lower, and more in all-out racing. It is one reason the sex gap in performance is smaller in longer, slower events than in shorter, faster ones.
Women Pace Smarter
One of the most consistently documented sex differences in endurance sport is pacing strategy. Women tend to run more evenly from start to finish, while men are more likely to go out fast and slow down. In the World Marathon Majors, the average difference between men’s first-half and second-half split times was about 3.4%, versus about 2.8% for women. After controlling for age and finishing time, women still showed a meaningfully smaller positive split.13Kinesiology. Pacing strategy of the finishers of the world marathon majors series
The same pattern shows up in ultramarathons. An analysis of 18 years of finishing data from the Western States 100-mile endurance run found that men had more pacing variability than women, with significant differences especially in younger runners and in certain middle-aged groups.14Scientific Reports. Pacing in ultra-marathon running: the Western States 100-mile endurance run 2006–2023 A systematic review of marathon pacing confirmed the broader trend: female athletes tend to display a more uniform and consistent pacing strategy than men.15PubMed Central. Pacing strategies in marathons: A systematic review
Why this matters for the endurance question: even pacing is almost always the fastest way to complete a long race. Going out too fast depletes glycogen stores and generates metabolic byproducts that accelerate fatigue. A runner who negative-splits or holds steady will often beat a runner of equal fitness who surges early and fades. Whether women pace better because of physiological differences (lower glycolytic capacity making it less tempting to push hard early), psychological tendencies, or social conditioning around risk-taking is not fully settled. The result, though, is a real-world performance advantage that partially offsets the cardiovascular gap in long events.
Estrogen and Muscle Protection
Estrogen appears to protect skeletal muscle from exercise-induced damage, an advantage that could help women recover faster between bouts of hard endurance training. In both human studies and animal research, females show lower levels of creatine kinase (an indirect marker of muscle damage) after eccentric and sustained exercise compared to males.16PubMed. Exercise-induced muscle damage and the potential protective role of estrogen The mechanism likely involves estrogen’s capacity to act as an antioxidant, stabilizing cell membranes and reducing the inflammatory cascade that follows hard exercise.17PubMed. Influence of estrogen on skeletal muscle damage, inflammation, and repair
Animal studies have been particularly revealing here. Ovariectomized female rats (whose estrogen levels drop sharply) show post-exercise muscle damage similar to males. When those same animals receive estrogen replacement before exercise, the damage is prevented. Perhaps most strikingly, males given estrogen treatment also stop showing post-exercise muscle damage.18PubMed. Prevention of exercise-induced muscle membrane damage by oestradiol The protective effect is clearly tied to the hormone itself rather than to sex per se. For premenopausal women with naturally high estrogen levels, this translates to a potential advantage in tolerating high training volumes with less muscle breakdown, though the practical magnitude of that benefit in real-world training remains an active area of research.
Estrogen levels fluctuate substantially across the menstrual cycle, which introduces another layer of complexity. Hormone changes during different cycle phases can affect substrate metabolism, cardiovascular function, temperature regulation, and psychological factors.19PubMed Central. Exercise performance at different phases of the menstrual cycle: measurements, differences, and mechanisms – a narrative review Whether these fluctuations meaningfully alter race-day performance for individual women is still debated, and the available evidence does not show large, consistent effects. But the underlying variability is real and adds a dimension to female endurance performance that has no male analog.
Running Economy Gives Women a Quiet Edge
Running economy, the amount of oxygen you burn at a given pace, is one of the best predictors of distance-running performance. When men and women with similar cardiovascular fitness levels are compared, women tend to have a lower oxygen cost of running across a broad range of speeds.20PubMed. Running economy in recreational male and female runners with similar levels of cardiovascular fitness In other words, women use less fuel per stride at the same relative effort. The reasons are not entirely clear, but lighter limbs, shorter stride lengths, and differences in tendon elasticity have all been proposed. Whatever the cause, this efficiency advantage means women can stretch a given level of aerobic fitness further in terms of sustained effort, even if their absolute aerobic ceiling is lower.
Running economy is distinct from maximal oxygen uptake, and the two can pull in opposite directions. Men’s higher aerobic ceiling gives them a bigger engine. Women’s better economy means they burn less fuel per mile. At shorter distances, the bigger engine wins easily because the race ends before fuel economy matters much. As distances increase, the economy advantage grows more valuable, which helps explain the shrinking performance gap in ultra-events from a metabolic standpoint.
How the Performance Gap Changes with Age
The sex gap in endurance performance is not fixed across the lifespan. In the world’s largest half-marathon, the GöteborgsVarvet in Sweden, women achieved their fastest race times at a younger age than men. The fastest female performances clustered in age groups under 35 and 35 to 39, while men peaked in the 35 to 39 bracket.21PubMed. Sex- and age-related differences in half-marathon performance and competitiveness in the world’s largest half-marathon – the GöteborgsVarvet This earlier female peak is consistent with the idea that women reach their endurance potential sooner but does not necessarily mean they decline faster.
In fact, at the Ironman triathlon in Hawaii, the performance gap between men and women has been closing over time, particularly in older age groups. Women older than 40 and men older than 44 significantly improved their performances across all three disciplines over a 25-year period, and the sex difference in total finishing time shrank for every age group between 40 and 59.22PubMed Central. Relative improvements in endurance performance with age: evidence from 25 years of Hawaii Ironman racing Some of this reflects the relatively recent growth in women’s participation in triathlon, meaning the talent pool is still deepening. But it also suggests that whatever physiological advantages women bring to endurance, those advantages may be relatively well-preserved as they age.
The Sociocultural Layer
Any discussion of sex differences in endurance has to acknowledge that women’s opportunities to compete and train have been restricted for most of modern sport history. Women were barred from the Olympic marathon until 1984. Prize money, sponsorship, coaching infrastructure, and media coverage remain unequal in many endurance disciplines. These disparities affect performance gaps in ways that are hard to fully separate from biology. A broad review of sex differences in running performance identified sociocultural, psychological, and sport-specific factors alongside physiological ones as contributors to the gap, and argued that there is scope to narrow it further by addressing inequalities in opportunities, provisions, and incentives.23PubMed Central. Expanding the Gap: An Updated Look Into Sex Differences in Running Performance
The participation effect is visible in the data. When ultramarathon fields have roughly equal numbers of men and women, the performance gap drops to as little as 1% to 3%. When fields are lopsided, with men outnumbering women five or ten to one, the gap looks much larger because the male field simply has more depth. As women’s participation in ultra-endurance sports continues to grow, we are likely to see the observed performance gap continue shrinking, though the biological sex differences in oxygen transport, lung mechanics, and heart size mean it is unlikely to disappear entirely.
Perceived Exertion and the Psychological Dimension
Endurance is not purely a matter of muscles and lungs. How hard you perceive an effort to be shapes how long you are willing to sustain it. Research on young people undergoing high-intensity rowing found that boys rated the exercise as subjectively more difficult than girls at nearly every age tested, even before the ages when boys develop measurably higher power output and metabolic responses.24PubMed. Sex- and age-related differences in the rating of perceived exertion after high-intensity rowing exercise during childhood and adolescence This study was conducted in children and adolescents, so extending the finding to adult endurance performance requires caution. But it raises an intriguing possibility: if females consistently perceive intense effort as somewhat less distressing, that psychological buffer could contribute to their more conservative pacing and willingness to sustain steady output over very long efforts.
Whether this pattern persists into adulthood, and how much of it is biological versus socialized, remains an open question. Pain tolerance, motivation, competitive framing, and risk appetite all vary between individuals far more than they vary between sexes on average. But the perception of effort is a real variable in endurance performance, and it intersects with the physiological story in ways that have only begun to be studied.
Where This Leaves the Question
The research draws a picture with two very different layers. At the tissue level, women have genuine endurance advantages: more fatigue-resistant muscle fibers, estrogen-mediated protection against exercise-induced damage, better fuel economy while running, and a tendency toward steadier pacing. At the whole-body performance level, men’s larger hearts, higher hemoglobin, and greater total muscle mass add up to faster finish times at virtually every race distance. Whether “endurance” means holding a contraction, completing a swim, or running across a desert changes which set of advantages matters more. As women’s participation continues to deepen across endurance sports, the gap between these two layers will likely keep narrowing, but the underlying physiology ensures it will not close entirely.