The Biology We've Been Ignoring in Women's Fitness

In 2019, researchers at McMaster University took a group of postmenopausal women and divided them into two groups. One group did standard cardio recommendations - walking, cycling, the kind of exercise every health organization tells you to do. The other group lifted weights twice a week. Heavy weights. Squats, deadlifts, presses. The kind of training most gyms don’t program for women.

After a year, both groups weighed the same. But their bodies were completely different.

The cardio group had lost muscle mass. Their bone density had declined. Their glucose metabolism had gotten worse despite exercising regularly. The lifting group had gained muscle, increased bone density, and improved their insulin sensitivity. Same time commitment. Opposite biological outcomes.

Nobody told them this would happen. The cardio group followed every guideline. They showed up, put in the work, tracked their steps. Their bodies deteriorated anyway because the program was designed for population averages, not for what actually happens to women’s physiology after menopause.

I keep thinking about this study when women like Sarah come into my office. She walked in three years ago carrying a contradiction I see almost weekly now. Forty-two, doing everything right by conventional standards, getting objectively worse by every biological measure that matters.

Five cardio classes weekly. Calorie tracking at 1,200 daily. Perfect app compliance. Her fitness tracker congratulated her constantly. Her body was failing.

Not failing from lack of effort. Failing because nobody had bothered to measure what was actually happening inside her. Her fasting glucose was 106 mg/dL, riding the edge toward diabetes. Her cortisol was elevated. Her testosterone was barely detectable. These aren’t minor deviations. They’re biological markers screaming that her program was destroying her metabolic health while telling her she was doing great.

This is what we’ve built. An entire industry that measures effort and compliance while ignoring the biology those efforts are supposed to improve. We track steps and calories and heart rate zones. We don’t track the muscle mass loss or bone density decline or insulin sensitivity deterioration happening underneath all that activity.

The gap between what we measure and what actually matters has created a generation of women who are working incredibly hard at the wrong things.

Here’s what took me years to understand about muscle mass in women. It’s not about aesthetics. It’s not about fitting into smaller jeans. Muscle tissue is your metabolic insurance policy for everything that goes wrong as you age.

When you have muscle mass, your body has somewhere to put glucose. Your muscles act like a metabolic sink, pulling sugar out of your bloodstream even when you’re sitting still. Lose that muscle and the glucose stays in your blood, bathing your cells in sugar, driving insulin resistance. This is why women lose 3 to 8 percent of their muscle mass per decade after thirty and see their fasting glucose climb even when they haven’t changed their diet.

The mechanism is direct. When you load a muscle progressively - and by progressively I mean heavier than last week, not the same three-pound dumbbells you’ve been using for two years - you create microscopic damage. That damage triggers a repair cascade. Your body recruits protein, hormones, and metabolic resources to fix and strengthen the tissue.

But here’s what they don’t tell you. That repair process doesn’t just make you stronger. It rewires your insulin signaling. It increases bone density at the exact attachment points where osteoporosis will try to break you later. It produces proteins called myokines that cross into your brain and protect against cognitive decline. You’re not just building muscle. You’re building metabolic resilience against every age-related disease that kills women.

Walk into a typical women’s group fitness class and none of this happens. The weights are too light. The programming prioritizes calorie burn over adaptation. You leave sweaty and exhausted but your muscle tissue received no signal to grow or even maintain itself. You’re burning calories in a way that will make you weaker over time.

I asked Sarah about her strength work. She told me about her “toning” classes with resistance bands and light dumbbells. I asked if she was lifting heavier than she was three months ago. She looked confused. The class didn’t progress. It was the same routine weekly. Her muscles had adapted to that stimulus years ago. Now she was just going through motions that cost her energy but built nothing.

Women with PCOS - and this affects up to one in five women - get told their hormones make it harder to build muscle. The research shows something different. Women with PCOS have musculoskeletal composition essentially identical to women without PCOS when you match for body composition. The metabolic differences correlate with insulin resistance and body fat percentage, not with androgen levels. Your hormones aren’t stopping you from building muscle. Your program is.

The protein situation is worse than most women realize. Standard recommendations are 0.8 grams per kilogram of body weight daily. That prevents deficiency if you’re sedentary. If you’re active and trying to maintain muscle mass against aging, you need at least 1.2 to 1.6 grams per kilogram. For most women, that’s roughly one gram per pound of ideal body weight.

Do that math. If your healthy weight is 140 pounds, you need about 140 grams of protein daily. Most women I see are getting 60 to 70 grams and wondering why their expensive trainer isn’t delivering results. You can’t build tissue without the raw materials to build it from. The program doesn’t matter if you’re not feeding the adaptation.

The running renaissance happened while I wasn’t paying attention. Suddenly half my female patients were training for marathons. Instagram filled with sunrise run photos and race medals. The culture felt positive and empowering. Women supporting women. Bodies in motion. Health through movement.

Then they started coming in with problems.

Irregular periods. Stress fractures that wouldn’t heal. Chronic fatigue they described as “pushing through.” When I looked at their training logs, I saw the same pattern repeating. Five, six days weekly in that uncomfortable middle zone. Not easy enough to recover from. Not hard enough to drive real adaptation. Exercise physiologists call it zone 3 or zone 4. I call it the place where effort goes to die.

Here’s what happens in that zone if you stay there too long. Your cortisol elevates and stays elevated. Elevated cortisol suppresses your hypothalamic-pituitary-ovarian axis. That’s doctor speak for your cortisol is telling your brain to shut down your reproductive hormones because your body thinks you’re in a chronic stress state. Which you are. Your periods become irregular. Your progesterone drops. Eventually you stop menstruating altogether.

This isn’t about being too thin or eating too little, though those make it worse. It’s about the signal your training is sending your endocrine system. The signal says: danger, sustained stress, not safe to maintain bone density or reproductive function. Your body starts breaking down what it considers non-essential. Bone density drops. Muscle protein synthesis slows. The low estrogen state accelerates bone loss beyond what you’d see in menopause.

A 2022 Lancet review quantified this. Women who maintain muscle mass and bone density through perimenopause show dramatically better metabolic health, lower cardiovascular risk, and preserved cognitive function compared to women who lose muscle even when their body weight stays the same. The intervention window is narrow. Once you’ve lost bone density, you’re trying to rebuild something that should have been maintained. It’s exponentially harder.

I pulled up Sarah’s training logs. Five cardio classes weekly. Two HIIT sessions. Two spin classes. One barre class. Every single session in that grinding middle zone. No progressive strength work. No truly easy recovery days where she could hold a conversation. No brief, genuine high-intensity intervals that would drive adaptation and then let her recover. Just sustained moderate-high stress day after day, week after week, year after year.

Her body had stopped being able to process glucose normally. Her cortisol was chronically elevated. Her testosterone was suppressed. She was pre-diabetic despite exercising more than 90 percent of the population. The exercise was causing the problem, not solving it.

The restructuring isn’t about doing less. It’s about doing different. Two to four days of actual strength work with weights that feel heavy. Two to four days of genuinely easy movement where you can hold a full conversation. One or two days of real intervals - hard enough that you can’t talk, brief enough that you actually recover. That pattern maintains your aerobic capacity while building the muscle and bone density your body needs to stay metabolically healthy.

This is where the template problem becomes impossible to solve with conventional tools. Sarah’s elevated cortisol and suppressed heart rate variability meant her body was operating in a chronic stress state. Her impaired glucose disposal meant she needed training that would improve insulin sensitivity without adding more stress. Moderate intensity work with actual rest between sessions. Movements that load muscles without spiking cortisol.

Her gym program couldn’t account for any of this. Neither could her app. They asked about her goals and her injuries and her availability. They never asked about her cortisol or her glucose regulation or her recovery capacity. Those variables determine everything about how her body would respond to training. They got ignored completely.

The obvious solution would be working with someone who understands exercise physiology and can adjust programming based on lab work and recovery data. That works beautifully. It’s also expensive enough that most women can’t access it long-term. Generic programs scale but they’re blind to individual biology. We’ve been stuck between personalization that’s inaccessible and accessibility that’s useless for most people.

I started seeing something change about a year ago. Not in the programs themselves but in what was becoming possible to measure and connect. Women were already wearing devices tracking heart rate variability, sleep architecture, resting heart rate. Labs were becoming easier to order and cheaper to run. The data existed. What didn’t exist was any system connecting those data streams in a way that could actually adjust programming.

This is where machine learning becomes useful instead of hyped. Not because an algorithm can design better workouts than a good coach. Because it can see patterns across variables that humans miss even when we’re looking for them. Your training response isn’t determined by any single factor. It’s determined by how your metabolic state, recovery capacity, hormonal status, inflammatory burden, stress load, and sleep quality interact. Non-linearly. Over weeks.

High cortisol changes how your body responds to training stress. Poor sleep impairs recovery which changes how quickly you can progress. Elevated inflammation means you need more time between sessions. A doctor reviewing labs quarterly might notice your glucose trending up. They won’t connect it to the training volume increase that happened six weeks earlier. They won’t notice that your HRV declined two weeks before your glucose shifted, giving a window to intervene before metabolic markers changed.

This is what systems like forge at moccet.ai were built to do. Not replace the judgment part. Map the patterns part. The system ingests your blood biomarkers, wearable data, training logs, calendar stress patterns, subjective recovery scores. Then it watches how these variables move together in you specifically. Not generic population truths about cortisol and glucose. Specific individual patterns. Your glucose regulation degrades when your training volume exceeds three high-intensity sessions weekly while your HRV is suppressed. That pattern is predictable enough in your data to adjust programming before your markers deteriorate.

They tested this approach with forty-seven women over twelve weeks. One started almost identically to Sarah. Fasting glucose at 108 mg/dL. Cortisol elevated. HRV suppressed. Following a popular high-intensity program six days weekly because that’s what the fitness industry tells women to do. The system looked at her biomarkers and rebuilt her program. Four days weekly instead of six. Moderate intensity instead of high. Extended rest periods. Movements specifically shown to improve glucose disposal.

Twelve weeks later her fasting glucose was 94 mg/dL. Her HRV had improved 23 percent. Her cortisol had normalized. Not through adding medication or supplements. Through training that matched her biology instead of fighting it. Through programming that could see the signals her body was sending and respond to them before they became disease.

I had Sarah get comprehensive labs. Not the basic panel her insurance would cover but the full picture. Metabolic markers, inflammatory status, complete hormone panel, vitamin D, magnesium. We started tracking her HRV and sleep quality with the device she already owned but had been using only to count steps and close activity rings.

The data told the story her body had been trying to communicate for three years. Chronic stress response. Cortisol elevated when it should have been low. Testosterone suppressed when she needed it for muscle maintenance. HRV chronically depressed, showing her autonomic nervous system couldn’t recover between training sessions.

The solution wasn’t more discipline or better calorie tracking. It was completely restructuring what training meant. Three days weekly of progressive resistance work. Real weight on a barbell. Squat patterns, hinge patterns, pressing, pulling. Loads that felt heavy. On other days, walking. Not power walking or incline walking or walking with a weighted vest. Just walking at a pace where she could hold a conversation. Genuinely easy. And actual rest days. Not yoga or “active recovery” classes. Days where she didn’t ask her body to perform.

We increased her protein to 120 grams daily. Most from plants but supplemented with some quality animal protein. We addressed her sleep, which had eroded to five hours nightly over the three years since her company’s Series B. We cut out the late-night email checks that were keeping her cortisol elevated precisely when it needed to drop.

Three months later she came back for follow-up labs. Her fasting glucose was 92 mg/dL. Normal range. Her body weight had increased by four pounds but she’d lost two inches around her waist. Muscle was replacing visceral fat, the dangerous kind that drives metabolic disease. Her joint pain had resolved. She could pick up her daughter without thinking about whether her knees would cooperate.

“I feel like myself again,” she told me. Not like a woman failing at fitness. Not like someone whose body was betraying her despite perfect compliance. Like someone whose program finally matched what her biology needed.

The difference wasn’t willpower. It was measurement. We measured the variables that actually determined her response to training. Then we built programming from those variables instead of from population averages or marketing research about what women think they want.

The fitness industry has built itself on a lie. Not the explicit kind where they tell you something false. The implicit kind where they let you believe that effort matters more than programming, that the woman who succeeds had more discipline than the woman who failed, that your inability to get results from their template represents your personal failure rather than their systemic one.

The evidence for resistance training in women has been clear since the 1990s. The American Heart Association published their 2024 recommendation building on decades of research showing that progressive strength training improves bone density, metabolic health, and functional capacity across the lifespan. We’ve known that muscle mass predicts healthspan better than BMI. We’ve known that women lose bone density rapidly during menopause and that the intervention window is narrow.

What’s different now isn’t the science. It’s the possibility of implementation at scale. Not through expensive personal training that works but remains inaccessible to most women. Through systems that take measurable biomarkers and wearable data and translate them into specific protocols that adapt as your physiology changes.

This matters especially during perimenopause and menopause when hormonal changes accelerate muscle loss and bone density decline. Traditional advice to “listen to your body” sounds reasonable until you realize your body is sending signals your conscious mind can’t interpret. You cannot feel your bone density declining or your insulin sensitivity deteriorating. Those processes happen silently while you follow programs that might be making them worse.

The technology for personalized programming exists now. Platforms like forge at moccet.ai integrate blood biomarkers with wearable data with training logs to map individual responses over time. Not generic advice about strength training being good for women. Specific data showing that your glucose regulation degrades when you do more than two high-intensity sessions weekly while your cortisol is elevated, and that this pattern is predictable enough to adjust your program before metabolic markers shift.

You can join the waitlist at moccet.ai/forge. What you get is a complete training program built from your actual metabolic state, free for early users. More importantly, you get to see what healthcare looks like when we stop applying population averages to individuals. The platform will eventually do for all of health what forge does for training now. Nutrition protocols adjusted to your metabolic markers. Sleep recommendations responsive to your recovery data. Stress management tied to your physiological state rather than generic meditation apps.

This is precision medicine applied to preventive health. Not replacing doctors but giving them and their patients tools to see patterns that emerge across weeks and months in ways quarterly visits miss.

If you’re reading this and recognizing your own story in Sarah’s, here’s what I wish someone had told her three years earlier.

Start lifting heavy things immediately. Not eventually. Not after you’ve lost ten pounds or “gotten in shape.” Your body doesn’t care about timeline. It responds to mechanical stress. Find a program built around progressive overload with compound movements. Squats, deadlifts, presses, rows, hinges. Start with loads you can handle safely but progress weekly. Add weight, add reps, add sets. The adaptation only happens when you progressively challenge your capacity.

Most gyms won’t guide you here because their business model runs on monthly memberships and group classes that keep you comfortable. You’ll need to actively seek out actual strength programming. Or use systems like forge at moccet.ai that build protocols from your metabolic state rather than from what market research says women want to hear.

Get comprehensive labs beyond what your annual physical includes. You want fasting glucose, HbA1c, complete lipid panel, vitamin D, thyroid function including free T3 and free T4, inflammatory markers like CRP and homocysteine. If you’re perimenopausal or your periods are irregular, add a full hormone panel - estradiol, progesterone, testosterone, FSH, LH. Don’t wait for symptoms. Your glucose can be trending wrong for years before it crosses diagnostic thresholds. Your bone density can be declining before you feel anything.

Consider getting a DEXA scan now if you’ve had any period of low estrogen. That includes hormonal birth control, excessive exercise, undereating, eating disorders, PCOS, early perimenopause. The guidelines say to wait until sixty-five for most women. The guidelines are designed for population screening, not for individual prevention. If you’ve had sustained low estrogen, your bones are at risk earlier.

Track recovery markers if you can. Heart rate variability, resting heart rate, sleep quality and duration. These aren’t metrics for athletes training for competition. They’re windows into whether your training load matches your recovery capacity. Your subjective feeling of fatigue lags behind your actual physiological state by days or weeks. By the time you “feel” overtrained, your HRV has been declining for two weeks and your metabolic markers have started shifting. The data can warn you before you break down.

Fix your protein intake. This might be the single most impactful change you can make immediately. Standard recommendations of 0.8 grams per kilogram prevent clinical deficiency if you’re sedentary. If you’re active and trying to maintain muscle mass against aging, you need at least double that. Work toward one gram per pound of your ideal body weight. If your healthy weight is 140 pounds, that’s 140 grams of protein daily. Track it for a week. Most women I work with are getting 60 to 70 grams and wondering why their training isn’t building anything. You can’t build tissue without providing the amino acids to build it from.

Restructure your training week. Stop grinding through that uncomfortable middle zone five days weekly. That zone where you’re breathing hard but can still talk, where most group fitness classes operate, is probably the worst place to spend your training time. It’s too hard to recover from but not hard enough to drive adaptation. Instead, separate your training into three distinct intensities. Heavy strength work two to four days weekly where you’re resting several minutes between sets. Genuinely easy movement most days where you can hold a full conversation. Brief, hard intervals once or twice weekly that are legitimately hard - you can’t talk during them - but short enough that you actually recover.

Understand that sleep and stress are training variables, not separate concerns. Calendar stress affects your training capacity as much as your previous workout volume. A week of poor sleep means reduced protein synthesis and impaired recovery regardless of how much you rest. High work stress means you need lower training volume right now, not heroic efforts to maintain your program. This isn’t weakness or lack of commitment. It’s biological reality that your body navigates whether you acknowledge it or not.

The fitness industry has built itself on something insidious. Not outright lies about what works. Something more subtle. They’ve let women believe that when the program doesn’t deliver results, the failure is personal. That success is about discipline and consistency, and if you’re not seeing results, you must lack both.

Sarah didn’t lack discipline. She had more discipline than most people demonstrate in any area of their lives. She showed up five days weekly for three years despite feeling progressively worse. She tracked every calorie. She never missed a scheduled workout. Her discipline was perfect. Her program was destroying her.

This is what happens when we apply population averages to individuals and call it personalized medicine. When we design programs for the average woman who doesn’t exist. When we measure compliance instead of outcomes. We create systems where women work incredibly hard at things that make them worse while being told they’re doing great.

The evidence for what actually works has existed for decades. Resistance training builds and maintains muscle and bone density across the lifespan. Higher protein intake supports muscle protein synthesis. Progressive overload drives adaptation. Recovery capacity determines how much training stress you can absorb. None of this is new. The American Heart Association published guidelines in 2024 building on research from the 1990s. We’ve known what works. We just haven’t built systems that implement it at scale for individual women.

What’s changed isn’t the science. It’s what’s become possible to measure and connect. Women are already wearing devices tracking recovery metrics. Labs are becoming more accessible. The data exists. What didn’t exist until recently was any system that could look at all these data streams simultaneously and adjust programming based on what they showed.

This is where platforms like moccet’s forge become relevant. Not as another fitness app promising results through templates. As systems that do what good coaching does but at a scale that makes it accessible. The platform looks at your blood biomarkers, your wearable data, your training history, your calendar stress patterns. Then it watches how these variables move together over weeks. Not generic population relationships but specific individual patterns in your biology. Your glucose regulation degrades when your training volume exceeds a specific threshold while your HRV is suppressed. That pattern is stable enough to predict and respond to before your markers shift.

You can join the waitlist at moccet.ai/forge and get access to this kind of programming, free for early users. What you’re getting isn’t motivation to work harder. You know how to work hard. You’ve been working hard at the wrong things. What you get is measurement sophisticated enough to show you what your specific biology needs, built from your actual metabolic state and recovery capacity rather than from demographic averages.

This is what the future of preventive medicine looks like if we’re smart enough to build it. Not more generic guidelines about diet and exercise. Systems sophisticated enough to map individual trajectories and intervene before population risk becomes personal disease. Right now this exists for training. Eventually it will exist for nutrition, sleep protocols, stress management, medication dosing. The technology works. The question is how many more Sarahs will break themselves following generic advice before we make personalized programming accessible to everyone who needs it.

The medicine of the future isn’t better population studies. It’s systems that understand you’re not a population. You’re a specific biological system with specific metabolic responses and specific recovery needs. Treat you that way and you get Sarah’s outcome - normal glucose, improved body composition, resolved pain, restored function. Treat you like an average and you get three years of hard work making things worse.