Mostly Men, Mostly Cyclists: How Well Does Triathlon Research Represent Women?

If you're a woman reading triathlon research, there's a quiet question behind almost every number you see: who was actually in this study? Often the honest answer is "a small group of trained men." That's not a conspiracy or a scandal. It's a long-standing habit in sport science, driven by convenience, cost and a reluctance to deal with the menstrual cycle in study design. But it has consequences for how confidently any female athlete should apply a finding to herself.

This article looks at how big the gap actually is, how it shows up in the triathlon literature specifically, where it is likely to matter and where it probably doesn't. It doesn't tell you to ignore research done on men. It's about knowing which conclusions have actually been tested on people like you.

How big is the gap?

The clearest measurement comes from an audit led by Emma Cowley and colleagues, published in 2021 under the title "Invisible Sportswomen." The team went through roughly 5,261 papers published between 2014 and 2020 in six popular sport and exercise science journals, covering more than 12.5 million participants. Their findings:

• 63% of publications included both sexes.
• 31% included men only.
• 6% included women only.
• Across all participants, 66% were male and 34% female.

The authors' conclusion was blunt: women "remain significantly underrepresented" and research conclusions "may apply primarily to one sex."

A second audit, published in the American Journal of Sports Medicine in 2025 by Ose and colleagues, revisited sports medicine research a decade after a 2014 audit of the same question. It analysed 1,441 studies published between January 2021 and August 2023. Women made up 43.95% of participants, up from 39% a decade earlier. That's real progress. But the study-level picture was less encouraging: 103 studies (7.15%) included only women, against 268 (18.6%) that included only men.

The two audits used different journals, time windows and fields, so their numbers aren't directly comparable. What they agree on is the direction. Women are a minority of participants, women-only studies are rare, and male-only studies remain far more common than female-only ones.

Counting women isn't the same as studying them

A headcount can make things look better than they are. If a study recruits women but doesn't record or control for where they are in their menstrual cycle, whether they use hormonal contraception, or whether they are perimenopausal, the result can blur real differences together.

The 2025 audit checked this. Only 66 of 1,441 studies (5.6%) took menstrual status into account in their design, and well under 1% met the higher-quality "silver" or "gold" standards the authors used for doing it properly. In 2021, a group led by Kirsty Elliott-Sale published a working guide in Sports Medicine setting out how to design studies with women as participants. It noted that most high-quality sport science data come from men, that the field lacked agreed definitions and methods for female-specific research, and that this had slowed the development of evidence-based guidelines for female exercisers.

Then there is age. Triathlon is a sport with a large masters field, and many female age-groupers are in their 40s, 50s and 60s. A 2024 editorial in the British Journal of Sports Medicine by McNulty, Olenick, Moore and Cowley pointed out that within the small slice of women-only research, perimenopausal and postmenopausal women are likely to be represented even less. They called it a gap that needs a deliberate "call to action." If you're a woman over 45 trying to apply research to your training, you are often extrapolating twice: from men to women, and from younger women to older ones.

What about triathlon specifically?

No one has yet published a formal audit of participant sex in triathlon research the way Cowley and Ose did for sport science in general. The closest thing is a 2025 narrative review by Loosli and colleagues in Frontiers in Sports and Active Living, which screened 662 articles and drew on 147 relevant papers comparing female and male triathletes. Its conclusion included a direct recommendation: future studies "need to balance the representation of female and male athletes in study cohorts to ensure that findings are relevant to both sexes," and to investigate the menstrual cycle, premenstrual syndrome, pregnancy and childbirth.

You can also see the pattern in the small laboratory studies that much practical triathlon advice is built on. A few examples from swimming and the swim-to-bike transition:

• The study most often cited for swimming the first leg at below race effort (Peeling and colleagues, 2005) tested nine highly trained male triathletes in a lab-based sprint triathlon.
• The study showing that drafting in the swim makes the following bike more efficient (Delextrat and colleagues, 2003) used eight trained male triathletes.
• A 2015 study on how racing a competitor improves cycling time-trial performance used fifteen male cyclists.

Even where women were included, numbers are often small. A 2000 study by Martin and Whyte comparing critical swim speed with lactate threshold in elite triathletes had eight participants: five men and three women. That's a reasonable lab sample, but three women can't tell you whether the result holds for female triathletes in general, and the paper wasn't designed to.

None of these studies is bad. They are well designed for their size, and their authors didn't claim to be studying women. The problem is what happens downstream. A result from eight men turns into a coaching rule, and the rule loses the information about who it was tested on. TriForward's own durability and power articles flag the same issue. Most of that literature comes from trained male cyclists who never had to run afterwards.

Where sex differences are documented

The case for caution isn't just "we don't know." In several areas relevant to triathletes, differences have been measured.

Aerobic capacity and thresholds

The Loosli review summarises that women's VO2max relative to body mass is typically around 20-25% lower than men's, while female triathletes tended to reach their lactate or anaerobic threshold at a higher percentage of VO2max. Practically, that means a training zone or pacing recommendation expressed as a percentage of VO2max may not land in the same physiological place for a woman as for a man. A zone anchored to a measured threshold, such as a test result, is more likely to transfer than one built from male averages.

The swim gap is the smallest

The same review reports that the performance gap between women and men in triathlon is smallest in swimming (around 12%), larger on the bike (about 15%) and largest in the run (about 18%). That's a population-level observation, not a promise about any individual. But it suggests that swim-specific findings may sit on firmer ground for women than run-specific ones. It's also one reason to be careful with "time saved" calculations derived from male race data.

Fatigue resistance depends on the task

In a 2014 review in Acta Physiologica, Sandra Hunter summarised a large body of work showing that women are often less fatigable than men during sustained muscle contractions at the same relative intensity. Crucially, that advantage depends on the task: contraction type, intensity, speed and the muscle group involved can all shift or remove it. Hunter also flagged that studies often include more men than women, which can hide real differences. For triathletes, the implication is that durability or fatigue findings measured in men shouldn't be assumed to apply the same way to women, in either direction.

The carbohydrate-loading lesson

This is the clearest example of how a study design choice can create an apparent sex difference. In 1995, Tarnopolsky and colleagues reported that female endurance athletes did not increase their muscle glycogen when dietary carbohydrate went from 58% to 74% of their energy intake, while men did. For a while, that was read as women being unable to carb-load effectively.

Two 2001 papers changed the picture. Tarnopolsky's group repeated the work with six trained men and six trained women and found that women did increase muscle glycogen, but only when total energy intake was raised alongside the carbohydrate share. James and colleagues fed trained women and men the same carbohydrate dose relative to lean body mass (12 g per kg of lean mass per day for three days). Women's glycogen rose from about 108 to 193 mmol/kg in one cycle phase and from 111 to 202 in another, compared with 109 to 183 for men. The authors concluded there was no sex difference when the dose was matched.

The lesson isn't about carb-loading specifically. It's that an early finding of a sex difference turned out to reflect how the women were dosed, mostly lower total energy intake, rather than biology. Small studies can mislead in both directions. They can hide real differences, and they can manufacture apparent ones.

Age-related decline starts earlier in the water

An analysis by Käch and colleagues of more than 410,000 Ironman results (329,066 men and 81,815 women, 2002-2015) found that age-related performance decline began earlier in swimming than in cycling and running for both sexes, from around age 25-29. For women, cycling and running declines began at 30-34. Women in the masters age groups are therefore working in the discipline where age starts to bite earliest, and they are also the group least studied in the lab.

Where the gap probably matters less

It would be easy to overcorrect and treat every male-derived finding as useless for women. That isn't justified either. The following is TriForward's inference, not a finding any single study reported. Principles that rest on very general physiology, such as progressive overload, specificity of training, the need for recovery, and the observation that steadier pacing is usually cheaper than surging, have no obvious reason to reverse in women. Where women have been studied for these principles, the direction of effect is typically the same, even if the size differs.

The menstrual cycle evidence is a good example of how the honest answer is often "smaller than you've heard." A 2020 meta-analysis by McNulty and colleagues pooled 78 studies and found that performance in the early follicular phase (the start of a period) was, on average, only trivially lower than in other phases. They rated the quality of evidence as low and recommended an individual approach rather than general rules. A companion meta-analysis on oral contraceptives (42 studies, 590 participants) similarly found any group-level effect on performance most likely trivial, and concluded the evidence doesn't support general guidance either way. In other words, female-specific research doesn't always find big differences. When it is done well, it often tells you the population average doesn't decide much and your own response matters more.

What's improving and what isn't

There is genuine progress. Women's share of participants in sports medicine research rose from about 39% to about 44% in a decade. Methodological guidance for studying women now exists. Female-specific meta-analyses have shown where effects are trivial rather than leaving the question to marketing. And triathlon reviews are explicitly calling for balanced cohorts.

What hasn't improved much is the small-lab-study layer, the eight-to-fifteen-person experiments that give us the mechanisms behind swim drafting, pacing and fatigue. Those studies are cheap to run with one sex and expensive to run properly with two. Many still recruit men only, and only around 1 in 20 studies accounts for menstrual status at all. Women in midlife remain close to invisible.

How to use this when you read anything

You don't need a statistics background to apply this. Before you change your training on the strength of a study or article, including this site's:

• Check who was tested. Look for the number of participants and their sex. "Trained triathletes" with no breakdown often means mostly or all men.
• Ask whether the claim depends on a physiological difference that is known to vary by sex. Aerobic capacity percentages, fatigue resistance, fuelling doses and age-related change are flags. Basic training principles are less so.
• Prefer advice anchored to your own measurements. A pace zone from your own test result, or a fuelling plan based on your own tolerance and body size, transfers better than a number copied from a male average.
• Give more weight to findings replicated in women, and treat a single small male-only study as a hypothesis for you, not a rule.
• Be equally sceptical of women-specific claims that outrun the evidence. Low-quality female-specific findings aren't automatically better than good male-derived ones.

The companion article, "Reading the Research as a Female Triathlete," turns these questions into a fuller framework and looks at where credible women-specific evidence can be found.

References

• Cowley ES, Olenick AA, McNulty KL, Ross EZ. "Invisible Sportswomen": The Sex Data Gap in Sport and Exercise Science Research. Women in Sport and Physical Activity Journal, 2021;29(2):146. doi:10.1123/wspaj.2021-0028
• Ose BM, Eisenhauer J, Roepe IG, Herda AA, Vopat BG, Vopat L. Where Are All the Female Participants in Sports and Exercise Medicine Research? A Decade Later. American Journal of Sports Medicine, 2025. doi:10.1177/03635465241278350
• Elliott-Sale KJ, Minahan CL, Janse de Jonge XAK, Ackerman KE, Sipilä S, Constantini NW, Lebrun CM, Hackney AC, et al. Methodological Considerations for Studies in Sport and Exercise Science with Women as Participants. Sports Medicine, 2021;51(5):843–861. doi:10.1007/s40279-021-01435-8
• McNulty K, Olenick A, Moore S, Cowley E. Invisibility of female participants in midlife and beyond in sport and exercise science research: a call to action. British Journal of Sports Medicine, 2024;58(4):180. doi:10.1136/bjsports-2023-107165
• Loosli M, Nikolaidis PT, Scheer V, Wilhelm M, Forte P, Andrade M, Rosemann T, Duric S, Cuk I, Knechtle B. Women in the triathlon: the differences between female and male triathletes, a narrative review. Frontiers in Sports and Active Living, 2025. doi:10.3389/fspor.2025.1567676
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• Tarnopolsky MA, Zawada C, Richmond LB, Carter S, Shearer J, Graham T, Phillips SM. Gender differences in carbohydrate loading are related to energy intake. Journal of Applied Physiology, 2001;91(1):225–230. doi:10.1152/jappl.2001.91.1.225
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• Käch IW, Rüst CA, Nikolaidis PT, Rosemann T, Knechtle B. The age-related performance decline in Ironman triathlon starts earlier in swimming than in cycling and running. Journal of Strength and Conditioning Research, 2018;32(2):379–395. doi:10.1519/JSC.0000000000001796
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