In schoolyards worldwide, the phrase “you run like a girl” is often used as an insult. We are used to seeing male athletes jump higher, lift heavier weights, and run faster than female athletes due to their greater muscle mass and VO2 capacity. This is why I was surprised to read about female athletes in ultramarathons matching and occasionally performing better than their male counterparts.
There are countless anecdotes of female athletes excelling in ultramarathons. Maggie Gutterl won the backyard ultramarathon by running longer than any athlete – male or female - after finishing 402 km in 60 hours. Courtney Dauwalter finished a 383 km race in about 57 hours, 10 hours faster than the second-place male athlete. Camille Heron won a 160 km race, beating all female and male athletes while drinking a beer in the final kilometres. While these individual accomplishments are impressive, do they indicate a larger trend in ultradistance running?
Current data shows that with increased distance, the performance gap between male and female athletes gets smaller. In professional marathons (26.2 miles / 42.2km), female athletes are about 12% slower than male athletes. And in one review of 50 and 100-mile ultramarathons, researchers found that in the 50-mile distance, female athletes were 9% slower than men and only 4% slower in the 100-mile distance. That said, one should keep in mind that data can be inconsistent and sometimes contradictory since only 20% of ultramarathon finishers since 1970 have been female, and the small sample size leads to high variability.
From aerobic fitness to muscle fatigue, stomach distress to fat percentage, there are a plethora of factors in addition to one’s sex as to what makes a great ultramarathoner. (Aside from the fact that all ultramarathoners are great. I mean who would voluntarily choose to run that type of distance?) In many areas, male athletes’ physiology gives them an advantage over female athletes, such as a higher maximal oxygen uptake. But in a few areas, female athletes seem to have the upper hand. One such area is muscle fibers and fatigue.
Tired Muscles
There are two main types of human skeletal muscle fibres: oxidative type-I, or ‘slow-twitch’ muscles, and glycolytic type-II, or ‘fast-twitch’ muscles. As their names hint, slow and fast-twitch muscle fibers have different strengths. Slow-twitch muscles produce less power but take longer to fatigue. Fast-twitch muscles produce more power but fatigue quickly. Having both types of muscles in our bodies allow us to perform diverse types of movement. Slow-twitch muscle fibres let us sit, stand, or in the case of ultra-athletes, run long and slow for hours on end, while fast-twitch muscles let us run to an appointment, play volleyball with friends, or sprint. Training with fatigued muscles is crucial during an ultramarathon since athletes need their legs to land and push off for hours without getting tired.
Like people, muscle fibres get tired when they run out of energy. So just as people will take in energy from coffee and bananas, the energy source for a muscle fibre is adenosine triphosphate (ATP). Slow-twitch muscle fibres take longer to fatigue, and it’s all thanks to mitochondria and oxygen. Mitochondria, appropriately nicknamed ‘the powerhouse of the cell’, help convert glucose (i.e., sugar) into ATP. When cells have sufficient oxygen, the mitochondria use aerobic respiration to create ATP. However, when cells don’t have enough oxygen, they resort to anaerobic respiration, and that takes place outside the mitochondria. Aerobic respiration is efficient but slow, producing 38 ATP for every single glucose molecule. By contrast, anaerobic respiration, while inefficient, is fast and produces 2 ATP for every glucose molecule.
Slow-twitch muscle fibres, the ones that are needed for longer distances, have many mitochondria and more myoglobin, a protein that delivers oxygen to our muscles. This allows these muscle fibres to generate ATP using aerobic respiration for hours on end – perfect for running 160 km races. Female athletes tend to have more slow-twitch muscle fibres than male athletes, which is one factor that can lead to success in ultramarathons!
Mind Over Muscle
Physiological differences in muscle fibres are only one of the reasons why female athletes excel in ultramarathons. Researchers found that female athletes have specific psychological attributes that contribute to the smaller performance gap in ultramarathons. One such attribute is pacing. A 2011 study of 3000 athletes from 14 US marathons found that female athletes were more likely to maintain their pace, while male athletes were more likely to slow down. This may be because male athletes tend to adopt riskier strategies such as starting too quickly, which then leads to tiring themselves earlier in the race than female athletes.
From mitochondria to muscle fibres to race strategies, there are a multitude of reasons why many female athletes perform better the farther they run. That said, there are also several factors that might disadvantage female runners relative to their male counterparts, and overall females do not outperform male athletes in ultramarathons. Beyond science, sociocultural factors such as camaraderie and sponsorships play a large role in the success of an athlete. Every year, there are more female athletes who finish ultramarathons and help inspire other women and gender minorities to participate in this traditionally male-dominated sport. With the shrinking performance gap between male and female ultrarunners and a few extraordinary performances from female athletes, maybe someday soon, “you run like a girl” will mean “you run like a world-class ultramarathoner”!
Maya McKeown recently graduated from McGill University with a Bachelors of Science (BSc) in Neuroscience and a minor in Mathematics.
Note: This article has been edited to reflect the latest research findings more accurately.
