During the 1990s some studies calculated that women would overtake men performance in the marathon event, because of their steeper increase in running velocity over the years.
Despite these studies, other models defended that there would always prevail a 10% difference advantage of males over females in running performance, due to their greater aerobic capacity (VO2max). This was confirmed by studying more than 90000 non-elite marathoners, where males had finishing times around 10% faster than females (4h28m vs. 4h54m).
But let´s talk about ultra-endurance sports, whose popularity has increased a lot in recent years. In these events, success is determined by a whole set of factors. We could highlight oxidative capacity, running energy cost, fatigue and pain resistance, nutrition, gastrointestinal system, experience, strategy, and motivation, among a few others.
Any runner needs a good set of skills to compete successfully in an ultra-marathon, but also be able to endure high training volumes and push their physiological limits to the edge.
On the marathon distance male/female ratios are around 50%, with males running a 10% faster than females, as we have mentioned previously. In ultra-endurance events though, female participants are often in higher numbers than males.
In these long events, the difference in finishing times between males and females goes down to 4% in ultra-marathons, 6% in ultra-distance open water swimming and is absent in cycling events longer than 200 miles.
Do these numbers mean that females are more physiologically prepared to endure the hardest of the events? Or these lower differences may be due to greater participation and training opportunities nowadays?
A recent article has reviewed the factors that could explain this potential advantage.
Fibres in human skeletal muscles can be type-I/slow or type-II/fast.
Type-I fibres are more resistant to fatigue, accounting in a study for 44% of the total fibres in females and only 36% in males. Additionally, they are associated with higher levels of capillarization and blood flow to the muscles.
Regarding muscle mass, males are more muscular, due to a greater diameter of the muscle fibres and not because of a higher number of them. Stronger muscles can restrict blood flow and lead to muscle fatigue earlier during isometric submaximal exercise.
Both factors would favour females having a greater resistance to fatigue than males.
Regarding the respiratory muscles, though, it seems that females are in disadvantage. Due to lung size, diameter of airways and the utilization of a greater percentage of VO2 during effort they could have lower oxygen economy during exercise.
Oxidative metabolism is essential in ultra-endurance exercise. The longer the distance the more intense is the use of free fatty acids.
Females show greater expression of genes associated with the metabolism of fatty acids, as it is the CD36, associated with a 4-fold increase of fatty acids metabolism in a mice model.
Thus, females could have a metabolic advantage during long duration exercise. Better efficiency would reduce caloric requirements and the need of exogenous carbohydrates.
Aerobic metabolism is limited by the maximal oxygen uptake. Superior performance in males is associated with higher VO2max values, trained or untrained.
Although the lower VO2max would certainly be a disadvantage for females in races of any distance up to the marathon, there are other factors influencing the performance in ultra-marathon events.
Thus, females have usually more conservative running strategies, explaining why they often are capable to maintain pace better than males. They take decisions to mitigate muscle damage and fatigue, key limiting factors of performance.
The most common disturbances in sports are nausea/vomiting and abdominal cramps, with a higher prevalence in females.
Despite this, due to better substrate efficiency, lower body mass and lower caloric needs females don´t need to consume as many carbohydrates as males. This is of special relevance because carbohydrates intake is the main cause of gastrointestinal disorders.
Thus, although female athletes may be more prone to gastrointestinal disorders, their lower caloric needs may compensate for these disturbances.
- Female athletes exhibit various characteristics that can confer them an advantage in ultra-endurance sports: a greater percentage of type-I fibres, greater fatigue-resistance, better substrate efficiency, lower energetic requirements and even be better at pacing.
- But some physiological characteristics can counteract these advantages, such O2 carrying capacity, gastrointestinal disorders and hormonal effects on cellular function and injury risk.
- Considering the pros and cons of the factors mentioned above, the current article concludes that the fastest females will never outperform the fastest males, except in ultra-distance swimming.
Do Sex Differences in Physiology Confer a Female Advantage in Ultra-Endurance Sport? Tiller, N.B., Elliott-Sale, K.J., Knechtle, B. et al. Sports Med (2021). https://doi.org/10.1007/s40279-020-01417-2