Ever joined your partner for a workout, stuck to the same plan, and watched him get fitter while you feel stuck or worse? Same. Years ago, I thought I was just missing some secret ingredient. Turns out, there’s more to it—and no, you’re not broken. From puberty to menopause, your body’s internal chemistry is rewriting the script behind the scenes. But here’s the kicker: For decades, most sports science research ignored these differences. Instead, women were expected to follow roadmaps paved for men. Let’s rip up that plan and ask: What if we started training and eating based on real women’s bodies, not outdated male models?
Rethinking the Rulebook: The Hidden Gender Bias in Exercise Science
If you’ve ever wondered why so much fitness advice seems to work better for men, you’re not imagining things. The world of exercise science has long operated on a rulebook that, intentionally or not, leaves women out of the equation. This isn’t just a minor oversight—it’s a systemic issue that shapes everything from the way studies are designed to the advice you hear in the gym.
Let’s start with the basics: most sports and health research relies on male participants. According to Dr. Stacy Sims, an exercise physiologist and nutrition scientist, the foundation of sports science is built on data from men—usually college-aged men between 18 and 22 (3:46-4:30). Why? The recruitment process itself is stacked in their favor. The language used in study invitations is often aggressive or competitive, which can be off-putting to many women (3:47-3:55). Plus, the time commitment and invasive procedures like muscle biopsies and blood draws are easier to fill with young men who have fewer barriers to participation (4:13-4:21).
But the real problem runs deeper. Women’s unique hormonal cycles and physiology are often ignored. “We have puberty, reproductive years, perimenopause, post-menopause, and menstrual cycle—each is a different hormone profile affecting the way we eat and train,” says Dr. Sims (0:17-0:19). Yet, research shows that these differences are rarely accounted for in study designs. Instead, data from men is simply generalized to women, resulting in protocols and recommendations that can be ineffective—or even risky—for female athletes.
Dr. Sims’ own journey is a case in point. As a university student, she participated in a metabolism lab and followed every protocol perfectly. Yet, at the end of the study, her results were tossed out. Why? “My results were thrown out because they didn’t match the results from the men,” she recalls (5:14-5:30). Her data was labeled an “anomaly,” not because she did anything wrong, but because her physiology didn’t fit the male norm. This isn’t just her story—it’s a pattern. Female anomalies are often discarded rather than investigated, further compounding the gender bias in sports science.
The consequences are real. Studies indicate that 60% of girls who were previously sporty drop out of sports by age 14 (1:01-1:05). Why? It’s not just about social pressures or lack of encouragement. As girls go through puberty, their bodies change in ways that affect movement and comfort in sports—like wider hips altering running mechanics (0:50-0:56). Yet, research and coaching rarely adapt to these changes. Instead, girls are left without guidance, and many simply quit.
Despite these challenges, progress is being made. Dr. Stacy Sims has published over 100 peer-reviewed studies on women’s physiology, pushing the field toward more inclusive, sex-specific research. Still, institutional and cultural biases persist, and the data gap remains wide. If you’re a woman, or if you coach or care for one, it’s time to recognize that the old rulebook doesn’t fit. Sports science for women demands its own playbook—one that respects and harnesses women’s physiology differences, rather than ignoring them.
“We have puberty, reproductive years, perimenopause, post-menopause, and menstrual cycle—each is a different hormone profile affecting the way we eat and train.” – Dr. Stacy Sims
“My results were thrown out because they didn’t match the results from the men.” – Dr. Stacy Sims
Hormones: The Invisible Hand Guiding Performance & Health
When it comes to women’s health and athletic performance, hormones are the silent architects shaping nearly every aspect of your journey. If you’ve ever wondered why the same training plan or nutrition strategy doesn’t work for you the way it does for men—or even for other women at different times—hormones are often the answer. Research shows that the menstrual cycle impact on training effectiveness, recovery, and even injury risk is profound and often overlooked (6.08–6.18).
Female bodies move through distinct stages: puberty, reproductive years, pregnancy, perimenopause, and post-menopause. Each of these phases brings a unique hormonal profile that affects fat storage, metabolism, muscle recovery, and especially heat acclimatization for women. For example, puberty isn’t just about visible changes. Hip and shoulder widening can shift your biomechanics, altering comfort and performance in sports and exercise. These changes can make certain movements feel awkward or even increase injury risk, especially if training programs don’t account for them.
The menstrual cycle itself is a master regulator. You’ll experience low and high hormone phases, with ovulation marking a key transition. During the follicular phase (low hormone), your body is generally more responsive to intense training and heat. But after ovulation, in the luteal (high hormone) phase, rising progesterone increases your core temperature. As Dr. Stacy Sims explains,
“When progesterone comes up after ovulation, our core temperature comes up—we don’t have as much heat tolerance.”
(8.18–8.21).
This shift isn’t just theoretical. Studies indicate that women require different protocols for heat acclimatization depending on their cycle phase. If you start heat training during the high hormone phase, you’ll need nine consecutive days to adapt. In the low hormone phase, you need a five-minute primer before beginning the nine-day protocol (9.07–9.28). Men, by contrast, can typically adapt in just seven days, regardless of hormonal fluctuations (9.00–9.05). This is a clear example of why women’s health demands its own playbook.
Ignoring these hormone-driven changes can lead to misunderstanding, frustration, and even dropout—especially during adolescence, when girls’ participation in sports drops sharply due to both physical and social discomfort (Notes). Fasting, calorie restriction, and supplements can also work differently—or even be risky—depending on your hormonal state. What works for a male athlete or a woman in one phase of her cycle might not work for you in another.
Key findings from decades of research, including over 100 peer-reviewed studies by leading scientists in the field (12.01–12.07), confirm that female athlete nutrition and training must be customized. Your hormonal state dramatically alters not just your comfort, but how effective your workouts and recovery will be. The takeaway? Understanding and honoring these invisible hormonal shifts is essential for maximizing both performance and long-term health.
The Anatomy of Exclusion: How Research Culture Leaves Women Behind
If you’ve ever wondered why so much of exercise science seems to treat women as an afterthought, you’re not alone. The roots of exercise science gender bias run deep, shaping everything from study design to the very questions researchers choose to ask. When you look at the history of sports science for women, you’ll quickly see a pattern: men are the default, and women are often left out or labeled as “problems to solve.”
Let’s start with how research studies are typically run. In most university labs, especially those focused on metabolism or physiology, the majority of participants are young men—usually college-aged, between 18 and 22 (4.23-4.30). Why? Because, as Dr. Stacy Sims experienced firsthand, men are considered “easier” subjects. The protocols—muscle biopsies, blood draws, repeated visits—are explained to large groups, but it’s mostly men who say yes. This isn’t just a coincidence; it’s a reflection of who’s designing the studies in the first place. Most principal investigators (PIs) and scientists in these fields are men (4.36-4.47), and their perspectives shape what gets studied and how.
Sims’ own story highlights how this exclusion plays out. As a second-year university student, she participated in a metabolism lab where she was one of the only women. She followed every protocol to the letter—her military upbringing made sure of that (5.09-5.14). Yet, after two weeks, her data was thrown out. Why? Because her results didn’t match the men’s. They were labeled “anomalous,” and the explanation she got was blunt:
“We don’t study women because they have a menstrual cycle and we just study men because they’re easier.” – Sims’ university professor (6.13-6.19)
This is a classic example of Stacy Sims research challenging the status quo. Instead of investigating why women’s results might differ—perhaps due to hormonal fluctuations—researchers simply exclude them, reinforcing the idea that men are the standard and women are outliers. Research shows that these cultural and funding pressures keep science stuck in a male-default loop, limiting our understanding and slowing real progress.
But this exclusion isn’t limited to the lab. Sims grew up in a military family, always “one of the boys.” She dreamed of joining the Army Rangers or Navy SEALs, only to be told by her father that she couldn’t—because she was a girl (6.36-6.58). That was her first taste of institutional barriers, a realization that being female meant being excluded from opportunities, no matter how qualified or determined you were.
When you throw away women’s data or ignore their unique physiology, you’re not just missing out on a few numbers. You’re missing the chance for real breakthroughs—new insights that could benefit everyone, not just women. Studies indicate that excluding women’s data limits advancement and perpetuates incomplete science.
| Scenario | Details |
|---|---|
| University Metabolism Lab | Only a few women included; their data often discarded as “anomalous.” |
| Military Ambitions | Army Rangers and Navy SEALs did not admit women at the time of Sims’ ambition. |
Both in the lab and in life, women’s unique needs and capabilities are often sidelined as outliers or problems to solve. This cycle of exclusion is why sports science for women needs its own playbook—one that recognizes women are not just smaller men, but individuals deserving of focused, inclusive research.
When Biology Meets Ambition: Milestones in Science, Sport, and Power
When you think about the intersection of athletic ambition and scientific discovery, Dr. Stacy Sims stands out as a trailblazer. Her journey is not just about breaking records in cycling, Iron Man, or ultra running—it’s about breaking new ground in the lab, too. What makes Stacy Sims research so unique is how her own athletic experiences sparked questions that science hadn’t yet answered. She didn’t just wonder how to fuel better or perform in the heat; she took those questions straight into the lab (8.00–8.06).
Imagine training for a race in Hawaii’s sweltering heat while living in the cool winters of New Zealand. That’s the kind of challenge that led Sims to study how women’s bodies respond differently to heat, especially across the menstrual cycle (8.41–8.57). Research shows that when progesterone rises after ovulation, women’s core temperatures increase, reducing heat tolerance. This means that female athletes can’t just copy male protocols for heat acclimatization. For men, seven days of sauna sessions might be enough to prepare for a hot race. For women, it depends on their menstrual phase: during the high hormone phase, nine days straight may work, but in the low hormone phase, shorter, repeated exposures are needed (9.00–9.28). These are key examples of women’s physiology differences that demand their own playbook.
Sims’ academic path is as dynamic as her athletic one. She earned her master’s in exercise physiology and metabolism at Springfield College, then dove into ultra running and Iron Man competitions (9.53–10.08). Her PhD focused on sex differences in heat performance, hydration, and how menstrual cycle phases and oral contraceptives affect female athletes (10.20–10.41). These studies didn’t just fill gaps in the literature—they answered real-world questions from her and her teammates.
Her research journey took her from Springfield to Stanford, the University of New Zealand, and AUT, where she continued to investigate female training adaptations in both elite athletes and everyday women. Whether you’re a parent, a weekend warrior, or a busy professional, Sims’ work offers practical insights that can help you optimize your own health and performance. As she puts it:
“I’ve always tried to bring what we learn from elite performance to the average person.” – Dr. Stacy Sims
Today, the impact of Stacy Sims research extends far beyond the world of elite sport. By translating high-performance principles into daily life, she’s helping women everywhere build resilience and longevity. Her projects now range from optimizing wellbeing for parents and workers to advancing women’s health research at AUT, with a focus on exercise, heat/cold exposure, and hormone therapy.
| Milestone | Details |
|---|---|
| Peer-Reviewed Studies Authored | Over 100 |
| Community Engagement | Above 53% of The Diary of a CEO audience listens regularly but hasn’t subscribed yet |
Major career milestones like these reflect how athletic competition and evidence-based science can push boundaries together. When you tailor elite sport insights to sex and life stage, research indicates you can transform not just performance, but everyday health.
Beyond the Menstrual Cycle: Sex Differences From Womb to World
When you think about the differences between men and women, it’s easy to focus on the obvious—like the menstrual cycle or physical changes during puberty. But research shows that women’s physiology differences actually begin much earlier, even before birth. Understanding these foundational differences is key to making sense of the unique health needs of women and why the “one-size-fits-all” approach in medicine and fitness often falls short (12.32-12.37).
Let’s start at the very beginning: conception. The moment a new life forms, chromosomes set the stage. Males have XY chromosomes, while females have XX. This genetic difference isn’t just a footnote in biology textbooks—it’s the root of many health vulnerabilities and advantages that play out over a lifetime. For example, studies indicate that pregnancy outcomes can be influenced by these chromosomal differences. If a mother experiences significant stress during pregnancy, her developing boy fetus is more likely to miscarry than a girl fetus. As Dr. Stacy Sims explains,
“When we look at stress and the mom under stress, we see there’s a higher incidence of miscarriage if it’s a developing boy fetus than a girl fetus.” – Dr. Stacy Sims (12.54-13.00)
This isn’t just a minor detail. The fact that male fetuses (with XY chromosomes) are more vulnerable to miscarriage under maternal stress highlights how men vs women metabolism and resilience start diverging long before birth. It’s a reminder that sex differences aren’t just about hormones—they’re also chromosomal, metabolic, and deeply contextual.
After birth, you might expect these differences to become more obvious. Surprisingly, that’s not the case. In early childhood, apparent sex differences fade into the background. Boys and girls often seem more alike than different, at least on the surface (13.05-13.11). But don’t be fooled—those differences are still there, quietly shaping development and health in subtle ways.
Then comes puberty, and suddenly, the contrasts between men and women’s physiology differences become impossible to ignore. Hormones surge, bodies change, and the gap in metabolism, muscle development, and even how each sex responds to nutrition and exercise widens dramatically. This is where many health programs start to pay attention, but by then, the groundwork has already been laid.
It’s not just biology at play, either. Social and environmental cues start to layer onto these biological differences, fueling disparities in health, performance, and opportunity. The world treats boys and girls differently, and these experiences interact with their biological makeup, sometimes amplifying or even masking underlying differences.
So, when you’re thinking about men vs women metabolism or planning for optimal health, it’s crucial to remember: these differences don’t start at puberty or end with the menstrual cycle. They begin in the womb, shaped by chromosomes, hormones, and the world around us. Effective health planning, as research consistently shows, starts with understanding these sex differences from conception onward. That’s why women’s health demands its own playbook—one that recognizes the unique journey from womb to world.
The Athletic Identity Crisis: Why Girls Drop Out & How We Can Flip the Script
Imagine this: by the age of 14, 60% of girls who once loved sports have quit (0:59–1:05). That’s not just a statistic—it’s a wake-up call. The reasons behind this mass exodus are layered, but puberty and the lack of tailored support top the list. As girls’ bodies begin to change, so do their experiences in sport. Hips widen, shoulders broaden, and suddenly, the movements that once felt natural—running, jumping, swimming—can feel awkward or even uncomfortable (0:50–0:57).
These physical changes, known as female training adaptations, are often misunderstood or ignored. Instead of being taught how to work with their new bodies, girls are left to navigate these shifts alone. The result? A spike in self-consciousness and a sharp decline in participation. The problem isn’t just the biology—it’s the lack of support and information that leaves girls feeling like their bodies are obstacles, not assets.
Sports science research, as Dr. Stacy Sims points out, has historically been based on male data (0:36–0:43). Training, nutrition, and recovery strategies are often generalized from men to women, overlooking crucial differences. For example, men might thrive on calorie restriction or fasting, but women’s bodies respond differently (0:44–0:48). Even the impact of caffeine on performance is under-researched in women (2:48–3:02). This gap in knowledge means girls and women don’t get the guidance they need—especially during puberty, when the menstrual cycle impact becomes a significant factor in training and recovery.
So, what can be done? Research shows that body-positive, customized coaching makes a real difference. When girls are empowered with knowledge about their physiology and taught strategies tailored to their unique needs, retention in sport improves. Hormonally informed coaching—where training is adapted to the menstrual cycle and puberty-related changes—can help girls stay engaged and confident in their athletic pursuits.
It’s time to flip the script. Instead of seeing female bodies as problematic, we need to recognize their strengths and potential. As Dr. Stacy Sims says,
“It’s never about how we can empower women to use their physiology to their advantage—so let’s change that.”
That change starts with education. Girls deserve to understand how their bodies work and how to train in ways that support their development. Proactive education, visible role models, and supportive environments are key to reversing dropout trends. When girls see their bodies as assets, not obstacles, they reclaim ownership of sport and health.
The athletic identity crisis isn’t inevitable. With the right knowledge and support, girls can thrive in sports—and beyond. By acknowledging the unique challenges and opportunities of female training adaptations and the menstrual cycle impact, we can create a new playbook—one that keeps girls in the game.
Wild Card: If Women Wrote the Manual – A Thought Experiment
Imagine a world where exercise science didn’t default to the male body as the “standard.” What if, instead, women’s bodies set the template for training, nutrition, and recovery? Let’s take a moment to flip the script—a true thought experiment that challenges exercise science gender bias and opens the door to real innovation.
From the start, most of us are handed advice built around a male-centric model. As Dr. Stacy Sims points out (0.17–0.21), the way we eat and train is often shaped by research that rarely considers female physiology. No one really told us how our unique profiles—like hormone rhythms or heat tolerance—could or should influence our routines. Not until recently, anyway.
Now, let’s imagine if women wrote the manual. What would change?
- Protocols built around hormone rhythms: Instead of ignoring the menstrual cycle, training plans would sync with it. You’d see advice on when to push hard and when to recover, based on real science about female training adaptations.
- Heat tolerance and hydration: Research shows that women’s bodies handle heat and fluid balance differently. If this was the norm, sports drinks, gear, and even gym temperatures might look very different.
- Real-world female priorities: Programs would consider not just performance, but also bone health, mental health, and life stages like pregnancy or menopause.
How would this shift affect sports, health, and even social beliefs? For starters, we might see less stigma around periods and more open conversations about what women need to thrive. If high school gyms and teams trained boys and girls differently from the beginning, both would benefit—each learning how to maximize their strengths, not just fit into a one-size-fits-all mold.
Here’s a light-hearted rant: What if, instead of treating women’s “anomalies” as errors, we celebrated them as discoveries? As Dr. Sims explains (12.27–12.41), sex differences aren’t just about the menstrual cycle. There are physiological distinctions from the earliest stages of life (12.45–13.17). Yet, these differences are often overlooked or dismissed in mainstream fitness advice.
‘What if the so-called anomalies weren’t ignore-worthy, but the whole point?’
Maybe, someday, we’ll all stop calling the cycle a “problem” and start calling it an “edge.” After all, most fitness advice could look radically different if female bodies set the template, not the exception. Challenging “default male” thinking doesn’t just benefit women—it unlocks massive innovation for everyone. Research indicates that embracing, not dismissing, difference is where real progress happens.
So, next time you hear someone say, “Women are just smaller men,” remember: The science says otherwise. And if women wrote the manual, the playbook for health and performance would be richer, more inclusive, and a lot more effective for all.
Conclusion: Start With Difference, End With Strength
When it comes to women’s physiology differences, the science is clear: women are not just “smaller men.” Your biology is unique, and it deserves its own playbook. For too long, health and performance advice has been based on male-centric models, leaving women to adapt, guess, or simply feel left behind. But research shows that real progress happens when you start by embracing—not erasing—what makes you different.
From the earliest stages of life, sex differences shape our health. For example, there’s a higher incidence of miscarriage with developing boy fetuses than girl fetuses, and this is linked to genetic differences between XX and XY chromosomes (12.56–13.03). After birth, those differences might seem subtle, but they’re there—waiting to become more apparent at puberty and beyond (13.03–13.17). These early distinctions remind us that women’s health isn’t just a variation on a male template. It’s a distinct path, with its own strengths and challenges.
Women who understand and embrace their physiology often turn obstacles into performance edges. Let’s take female athlete nutrition as an example. Instead of copying what works for men, you can experiment with strategies tailored to your hormonal cycles, metabolism, and recovery needs. Studies indicate that science-backed, sex-specific strategies lead to empowerment and improved results. It’s not about working harder to “catch up”—it’s about working smarter, with evidence that fits your body.
Shifting from frustration to empowerment isn’t always easy. It requires knowledge, a willingness to experiment, and sometimes a change in attitude. Maybe you’ve felt frustrated by advice that doesn’t fit, or by comparisons that make you feel like you’re falling behind. But remember: you’re not on the same track as the men around you. And that’s not a weakness—it’s a source of strength. The future of health is personalized, and you deserve more than guesswork. You deserve evidence, empathy, and high standards.
Progress in women’s health comes from advocacy and empathy, too. When you advocate for better research, demand answers, and support others on their journey, you help drive change. High standards—expecting more from science, coaches, and yourself—push the field forward. Each time you choose to own your physiology, you chip away at old myths and open the door to new opportunities.
Own your physiology. There’s power in difference.
So next time you feel like you’re lagging behind, pause. You’re not behind—you’re on your own track. By respecting your unique biology and seeking out strategies that fit, you can thrive. Women’s health and performance don’t just survive in the face of difference—they thrive because of it. And as more women turn knowledge into action, obstacles become stepping stones, and myths give way to progress.
FAQ: Your Questions on Female Physiology, Performance, and Personalization
When it comes to female athlete nutrition and understanding women’s physiology differences, there are always more questions than answers—especially as research, like that of Dr. Stacy Sims, continues to evolve. Let’s dive into some of the most common questions women ask when trying to personalize their approach to health, fitness, and performance.
How often should women adapt training around their cycle?
If you’ve ever wondered whether you should change your workouts based on your menstrual cycle, you’re not alone. Research shows that hormonal fluctuations can affect everything from energy levels to recovery rates. Dr. Stacy Sims’ research emphasizes that there’s no one-size-fits-all answer, but paying attention to your own cycle patterns can help you optimize training. Some women notice they feel stronger in the follicular phase (the first half of the cycle), while others may need to adjust intensity or volume during the luteal phase. The key is curiosity and ongoing adaptation—track how you feel, and don’t be afraid to experiment.
Are fasting and calorie restriction safe for women?
This is a hot topic in female athlete nutrition. Studies indicate that women’s physiology responds differently to fasting and calorie restriction compared to men. Extended fasting or severe calorie cuts can disrupt hormones, especially if you’re active or under stress. Dr. Sims often cautions that what works for men may not be safe for women, especially during reproductive years. If you’re considering fasting, it’s best to consult a professional and listen to your body’s signals.
Why do girls drop out of sport at puberty—and what helps?
Puberty brings a wave of changes, both physical and emotional. According to research discussed around 12:39-13:15 in the transcript, differences between boys and girls become more pronounced at puberty, impacting confidence, body image, and performance. Many girls leave sports due to lack of support, embarrassment, or not understanding these changes. Creating supportive environments, normalizing conversations about periods, and providing female-specific coaching can help keep girls engaged and thriving in sport.
What’s Dr. Stacy Sims’ top advice for everyday women wanting better health?
Dr. Sims’ message is clear: women are not just smaller men. Her top advice is to embrace your unique physiology, stay curious, and personalize your approach. That means tuning into your body, adapting your nutrition and training, and seeking ongoing support. As she often says, “Ongoing support, curiosity, and adaptation are key for thriving at every age.”
Can these insights be applied for older women or post-menopausal athletes?
Absolutely. While much of the research focuses on premenopausal women, the principles of personalization and adaptation apply at every stage of life. For post-menopausal athletes, changes in hormones mean shifts in nutrition and training needs. Staying informed and flexible is essential—what worked at 25 might not work at 55, and that’s okay.
Are there specific supplements women should (or shouldn’t) try?
Supplement needs vary widely, and there’s no magic pill. Some women benefit from iron, vitamin D, or omega-3s, especially if blood tests show deficiencies. However, research shows that “more” isn’t always better. It’s best to base supplement choices on individual needs, ideally with guidance from a healthcare provider.
In summary, the science of female athlete nutrition and women’s physiology differences is always evolving. Personalized advice is best, but evidence-based trends can guide you. Stay curious, keep adapting, and remember: your health journey is uniquely yours.
TL;DR: Women aren’t just smaller men—training, nutrition, and health must be shaped by real female physiology. Understanding and embracing these differences empowers women to achieve better results, resilience, and well-being, no matter their life stage.
Hats off to The Diary Of A CEO for the thought-provoking content! Take a moment to check it out here: https://youtu.be/It5_C6AF1pk?si=NU3OGHUixietIaux.
