When the first women were finally allowed to run marathons in the 1980s, they faced more than just the physical challenge of 26.2 miles. Skeptics had warned that the distance would be too gruelling for the female body — and some went further, claiming it could damage a woman’s reproductive organs. Those fears, rooted in outdated notions rather than evidence, were quickly shown to be baseless once women began crossing finish lines. This Sunday, nearly 60,000 people will take on the London Marathon, and based on recent years almost half of them will be women.
From scepticism to record entries
The London Marathon launched in 1981, a time when women’s participation in long-distance running was still a novelty. By 2024, the event had grown so popular that more than half a million people entered the ballot for places — a world record for marathon applications. Of the 53,723 who finished last year, 42 per cent were female and 58 per cent male. The field is also getting younger again after a decade-long shift toward older runners; the 2024 marathon saw a slight increase in the proportion of entrants under 40.
The idea that women could not handle the distance was disproved almost as soon as they were allowed to race. Yet physiological differences between the sexes do explain why men tend to finish faster. In last year’s London Marathon, the average finishing time for men was four hours and 12 minutes, while women averaged four hours and 49 minutes — a gap of 37 minutes. In 2022 the difference was similar: men averaged 4:21, women 4:57. The gap narrows among elite runners, but on average women also slow down slightly less than men between the first and second halves of the race.
Anatomy of the stride: the Q angle and its consequences
Much of the difference in running gait comes down to skeletal structure. Men are, on average, 9 per cent taller than women, but their legs are proportionally even longer. Yann Kai Oh, a running researcher at Leeds Beckett University, explains that women’s thighs are 12 per cent shorter than men’s, while their torsos are longer. “Men’s legs are longer and women have a longer torso in general,” Oh said.
The most important anatomical distinction for runners, however, involves the hips and legs. A line drawn straight down the thigh from the hip to the knee forms one angle with a line from the outside of the hip to the knee. This is called the Q angle, and it is wider in women — about 17 degrees, compared with 14 degrees in men. The reason is that women have wider hips, shaped for childbirth, combined with shorter legs.
A wider Q angle changes the way the body absorbs impact during running. Video analysis shows that it causes the knees to roll inwards when the foot strikes the ground, creating a knock-kneed appearance. Dr Philip Nagy, a biomechanist at Lancaster University, says this alignment puts extra stress on the knee joint. “That knock-kneed alignment creates greater forces on the knee,” he explained. Studies have found that runners of either sex with wider Q angles are more prone to knee injuries, and female runners sustain more knee injuries than male runners overall.
The wider Q angle also affects the foot. It tends to make the foot roll inwards on landing — a gait known as overpronation — which can increase the risk of foot and ankle injuries. Many running shoes are designed to correct overpronation with extra cushioning on the inner sole, while other shoes support underpronation (where the foot rolls outwards). Although some experts now question whether such corrections are necessary, Dr Nagy believes limited support can help, provided the shoes “still allow the feet to move naturally”.
Beyond the Q angle, female runners exhibit distinct lower-limb biomechanics. Research shows they have greater hip flexion, adduction and internal rotation angles, along with smaller knee flexion angles, compared with male runners. During the stance phase of running, women tend to have less knee flexion and more knee valgus — the knock-kneed position — and may have lower hamstring activation, which can increase the load on the anterior cruciate ligament (ACL). This helps explain why women are two to eight times more likely than men to suffer ACL injuries. Knee injuries account for 40 per cent of all injuries in female runners, compared with 31 per cent in men, and patellofemoral pain syndrome is also more common in women.
Periods, hydration and other health risks
The menstrual cycle can also affect performance and injury risk, though the evidence is mixed. Many female athletes report feeling worse during certain phases, particularly the early follicular and late luteal stages, but objective measures often show inconsistent effects. Some studies suggest reduced performance in the late luteal phase due to decreased neuromuscular efficiency, while others indicate improved endurance in the follicular phase because of greater carbohydrate utilisation. Hormonal fluctuations in oestrogen and progesterone can influence mood, motivation and energy availability. The impact varies widely between individuals, making cycle tracking important. On race day, period pain is unlikely to help anyone, and hormonal shifts may also affect collagen elasticity in the knee, potentially raising the risk of ACL injuries.
A more concrete danger — and one women are more vulnerable to — is drinking too much fluid during a marathon. Overhydration can cause sodium levels in the blood to fall dangerously low, leading to confusion, seizures and even death. Women are at higher risk because they tend to be smaller, have lower total body water and smaller extracellular fluid volumes, and often take longer to finish the race, giving them more opportunities to drink. Research shows that risk factors include gaining substantial weight during the race, consuming more than three litres of fluids, drinking at every water station and having a low body mass index. Losing less than 0.75 kg of body weight during a marathon increases the risk of hyponatremia seven-fold.
Until about a decade ago, common advice was to drink at every water station. That changed after marathon deaths attributed to overhydration. Dr Richard Blagrove, a sports scientist at Loughborough University, now advises runners to drink enough to quench their thirst. “Most people will definitely need to take on board fluids during the marathon,” he said. “But if people are forcing a lot of fluid down them, particularly in the early stages, that’s not necessarily a good thing.”
Strength training can reduce the risk of injury for both men and women. Dr Nagy noted that “the difficulty for runners is finding time to do the strength training, if they’re running 50 kilometres a week.” For female runners, targeting the hips and glutes is especially important, as weak glutes and hip abductors are linked to conditions such as IT band syndrome and runner’s knee. Recommended exercises include squats, deadlifts, lunges, push-ups, rows, planks, glute bridges and calf raises, with two to three strength sessions per week. Postpartum runners may also need to focus on pelvic floor and core strengthening.