Habits and Hustle - Episode 464: Dr. Stacy Sims: Why Women Are Not Small Men and Need to Train Completely Differently

Episode Date: July 4, 2025

Why do women and men get vastly different results from the same workout and diet plan? In this Fitness Friday episode on the Habits and Hustle podcast, I sit down with Dr. Stacy Sims, exercise physiologist, who reveals the differences that affect every aspect of how women should approach fitness and nutrition. We dive into how puberty creates a biomechanical shift that changes everything and reveal why popular fitness trends like Zone 2 training and Orange Theory classes may actually be working against women's biology. We also share the specific strategies women need to combat muscle loss, maintain bone density, and optimize body composition. Dr. Stacy Sims is an international exercise physiologist and nutrition scientist who specializes in sex differences in training, nutrition, and environmental conditions. She's the author of "Roar" and "Next Level" and has spent decades researching how women's unique physiology requires different approaches to health and fitness. What we discuss: Why women are born with different muscle fiber types than men  Why Zone 2 training isn't optimal for most women throughout their lives The importance of power-based and strength training for women's longevity How perimenopause changes training needs Why moderate intensity workouts can increase cortisol and visceral fat Why women need heavy lifting (0-6 reps) during perimenopause  Why women are more prone to ACL injuries and frozen shoulder   Thank you to our sponsor: Momentous: Shop this link and use code Jen for 20% off Therasage: Head over to therasage.com and use code Be Bold for 15% off  TruNiagen: Head over to truniagen.com and use code HUSTLE20 to get $20 off any purchase over $100. Magic Mind: Head over to www.magicmind.com/jen and use code Jen at checkout. Bio.me: Link to daily prebiotic fiber here, code Jennifer20 for 20% off.  David: Buy 4, get the 5th free at davidprotein.com/habitsandhustle. Find more from Dr. Stacy Sims: Website: https://www.drstacysims.com/  Instagram: https://www.instagram.com/drstacysims  Find more from Jen: Website: https://www.jennifercohen.com/ Instagram: @therealjencohen Books: https://www.jennifercohen.com/books Speaking: https://www.jennifercohen.com/speaking-engagements

Hi guys, it's Tony Robbins. You're listening to Habits and Hustle. Crush it! Hey friends, you're listening to Fitness Friday on the Habits and Hustle podcast, where myself and my friends share quick and very actionable advice for you becoming your healthiest self. So stay tuned and let me know how you leveled up. Before we dive into today's episode, I want to thank our sponsor, Momentous. When your goal is healthspan, living better and longer, there are very few non-negotiables. One of them, quality. And when it comes to supplements designed for high performers, nobody does it better than Momentus. Momentus goes all in on NSF certification, which means every single batch is tested for heavy

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Just act now. Start today. GEN for 20% off. Just act now. Start today. Jen for 20% off. Livemomentous.com. I like to kind of start this conversation when we look at the sex differences that exist at birth. So that's like without our hormone fluctuations from our menstrual cycle and stuff.

So when we look at XX versus XY, because that's the primary area of research that we have, very binary, but that's all we have at the moment. If you are born XX, then you have more endurant type fibers. So your slow twitch, your oxidative, very aerobic type fibers. And with that comes a lot of mitochondria work. So that means your body's really able to take fatty acids and

use it, use oxygen and go long and slow. When we look at XY, they're born with more of the fast twitch glycolytic power base fibers. So good at speed, good at quick reaction time, good at doing super high-intensity work, and they have to work on developing that aerobic system. So as we feed forward and see at the onset of puberty what happens is there's another divergence where with the what we call the epigenetic exposure or the situational change that happens with estrogen, progesterone, to some extent testosterone in girls.

We have a change in all of our biomechanics. So our center of gravity goes from being up in the chest area down to the hip area. Our hips widen, our shoulder girdle widens, but we're not told about this. So we feel ungangly in our bodies. We aren't taught how to run again, how to jump, how to swing, how to land, or any of those things. You're just, well, you are at this point, you get your period, we know girls drop out of sport, but it has to do with the fact that the actual biomechanics of the body have changed. So when we start looking at all these trends that are out there, and about doing like

zone two work and improving our aerobic capacity and trying to do ketogenic diet for improving our fat burning capacity. All that's based on male data because being born that xx you already have all of that capacity. What we need to work on throughout our entire life is working on that power base and the fast twitch and I say that because we want to be able to produce power, we want to be able to run fast to jump to land to have good coordination. But more than that, when we look at longevity, then we see this is really important in peri- and post-menopausal that we keep producing lactate for brain health.

Because if we keep producing lactate from that fast twitch and that higher intensity work that we've been trying to build throughout our life, we are slowing the rate and the risk for Alzheimer's and dementia. So when we see that sex difference in Alzheimer's and dementia, it comes down to the type of muscle fibers and the metabolism that we've been exposed to throughout our life.

So that's why it's like, okay, if we look from birth all the way through to the end of life, there are unique things that women need to do to keep progressing and improving their health for longevity and performance, whereas men are more of a linear, because they don't have all of these changes that women have with regards to biomechanics and hormone exposure. So of course it makes sense that you see all this data that comes out for men and men are scribing these protocols and they're improving, that when you take that and put it into certain points within a woman's life, they're not going to respond the same way because physiologically and biomechanically, they are not the same as where that data originated from.

Because even women who have, I'll talk about that later on, but like later on in life, but I noticed, I saw something about how women have more ACL issues, right? And we have all, where are the other injuries and things that women are more prone to injury wise or happen to women versus men because of our biomechanics? And then also how should we train for our biomechanics? And then also, how should we train for our biomechanics? So women are more quad dominant, just the way our posture is and our center of gravity. So this already predisposes us to change a direction injury, soft tissue injury.

That's part of the reason why we see a greater predisposition in ACL injury, because we don't have the hamstring strength to counter some of those cutting motions that causes an ACL tear. So when we're looking at that and what we need to do is we need to put that focus away from the knee and the lunge and all that quad dominant type work, put it posterior. So you're looking at developing the glutes and the hamstrings, a lot of extension work. And we see that when women start to do that, they reduce their injury risk and they have better posture and cutting motion.

And when we're looking at things like what FIFA has put out for warm-up, it's all about warming up the posterior chain and trying to get those muscles firing as a counteract to some of those cutting motions that predispose women to ligamentary tears. We also see that as we get into perimenopause, there is a definitive increase in plantar fascia issues and frozen shoulder or bursa in your shoulder. And that has to do with the changing of the tensile strength in the ligaments as well as a weakening in the muscle contraction. So again, we're looking at what do we need to do to prevent that. We need to keep the strengthening and the faster type power-based action to create an environment that reduces injury,

reduces the inflammation of the tendons, and allows better range of motion. So when we look at men who are in their 40s, rarely do we hear about a plantar fascia issue. You look at women in their 40s, it's one of the leading issues that make them go see a physical therapist or an osteo or a chiro. It's an inherent sex difference, right? I can see you're like, you've probably experienced it. I'm laughing, crying and laughing at the same time because I've had, I'm in my 40s, I had the frozen shoulder for two years almost, it's finally now dissipated.

And I had the plantar fasciitis and I didn't realize that those were two things that went with my age. I had no clue until I went down. I was like, I thought maybe I pulled a muscle in my shoulder and the guy was like, no, you have frozen shoulder. And I'm like, what the hell is that? Like, how does someone get that? They're like, you're old, basically,

is what he says to me, right? And I never understood, like, I get the ACL because you're right. Like, we are quad dominant, right? And women tend to do those lunges and those squats. But the frozen shoulder, I didn't understand. I did not understand that. Yeah, so frozen shoulder has to do with we have a wider shoulder girdle because our hips have widened. Yeah.

But if you think about all the metrics that we've taught to do pushups, pull ups, they're all in a grip strength or a grip width that's based on male data, male physiology. Right. Because you know, if you go to do a pull up and you're a bit wider, like no, more narrow. So it puts a lot of strain where it shouldn't. Same with pushups, they're trying to teach you to be really tight and use more tricep. But our shoulders as women, we need to be wider. So it's just that inherent that we're and we tend to like when we get our 40s, we're like, okay, yeah, I really, most of us have a challenge and we want to

accomplish so it could be a push up or pull up, or we start doing more up and push pull motions. And even like lifting things overhead, groceries and all that kind of stuff. It's just the mechanics that we are not taught how to actually maximize with our wider shoulders. And you couple that with changes in our estrogen progesterone ratio, which changes tensile strength

and the actual texture kind of of our tendons and our bursa. And it just comes on. So I'm always trying to reteach from a young age, from puberty onward, how we move in these new mechanics to reduce injury risk at the onset of puberty, but also as we get older into peri and postmenopause. Kite So what should we be doing to offset that type of injury in the frozen shoulder? What is a good exercise to focus on? Dr. Kite So a lot of it is you're dropping your traps and you're pulling back, so you're doing a lot of rhomboid work.

You're also looking at where you're placing to be able to use more of your back muscles when you're doing a push-up. Also back muscles when using a pull-up instead of relying on the shoulders. And the same when you go to lift something up. Most of the time we're lifting or hitching our shoulders. If we're thinking about dropping our traps and we're using our back muscles to pick something up and then extending through the hips to lift it up, we're reducing the load in our shoulders and in that rotation, which reduces the whole onset of injury or soft tissue damage that can perpetuate injury.

And what about for ACL issues to kind of strengthen? What do you think is the best way to strengthen our posterior chain? All the glute work where you're thinking about deadlifts, you're thinking about Romanian deadlifts, you're thinking about hip or glute bridges, hip thrusts, all of those things, right? And really focusing on getting the hips strong. And a lot of other things that can perpetuate it is we have weak and tight hip flexors. So really working on developing that hip flexor strength so we can lift the hip and the leg

up and over instead of stumbling. Right. Oh, that's good. Right. strength so we can lift the hip and the leg up and over instead of stumbling. Right. Oh, that's good. Right. Let's quickly talk about a health issue that affects almost all of us. Fiber deficiency. Did you know that 95% of people don't get enough fiber in their daily diet? I was shocked when I learned this, because fiber is truly the foundation of overall wellness.

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of daily prebiotic fiber. That's BioMe.com code Jennifer20 for 20% off. Grab it today. And so, but as we get older, we talked about, you were saying like, as you're getting to perimenopause, menopause. Let's stay with that, because I think my audience can appreciate that. That's something that I feel like that's become super trendy now, too. Like, I don't remember, maybe because I'm at that age,

I'm seeing it more? Or is it something that... No, it's come up. Right? Definitely. Yeah, absolutely. And it's scary because the conversation has not been out there. And now it's a buzzword conversation has not been out there. And now it's a buzzword and everybody's grabbing onto it. And there's a lot of misinformation that's being spread.

And from a scientific point of view where I've been in the whole perimenopause, menopause research world for 15 or so years, to all of a sudden see the conversation out there and people are misconstruing a lot of the research or they're in one camp bucket of pharmaceuticals or one camp bucket of suffering through it and none of it's actually right. And then there's just so much, it's just so noisy. So I'm like trying to cut through the noise and go, okay, ask me what you wanna know

and we're gonna unpack it for you Thank you Cuz I think that's a great point cuz like I said, I see it if you if you scroll on social media every second post is about menopause and or add or carry menopause and I think the problem is there is so much noise and and so much information people are very confused I know I'm confused. Absolutely. Right? And I do this for a living.

And I've had like all the same top doctors come on here and talk about it, and I'm still confused because they don't even agree with each other. You know what I mean? Exactly, exactly. That's it, yeah. And I'm finding that a lot of the, and I don't want to put people on the bus,

but unfortunately those with some of the loudest microphones tend to not stay in their lane. And what I mean by that is like, if you're an endocrinologist or you're a medical specialist and you understand things like hormone therapy, then talk about that, right? If you're someone who's like me, who's an exercise physiologist and a nutrition scientist

understands that and environmental stress, I talk about that. I can give a high touch on hormone therapy, but I'm not going to be a definitive person on that because that is not my area. I'm going to refer you to Jen Gunter or Mary Claire or some of the other experts that are out there who actually know the nuances of hormone hormone therapy and how it can be applied to you as an individual. So that's part of the confusion too, because everyone's kind of in their silo and trying to be an expert in everything instead of saying, you know what, this is my lane and these are the things that I know and I can talk at a high point on some of the things I don't know,

but I really want you to seek out these experts who know what it is in that lane. Right. I think there's so much confusion. So let's start with perimenopause, right? Because it's before menopause. How should women be training, eating, recovering in that space for optimal results? So as a physiologist, I'm going to explain what's happening on the the undercurrent of everything. So we look at estrogen, progesterone and testosterone, and they affect every system of the body. So when we start losing the higher doses and pulses of estrogen, and we have more and more an ovulatory cycles, so we don't necessarily produce progesterone. Every system gets affected specifically bone and muscle. So we'll have women who are complaining

about waking up feeling squishy overnight and they can't even open like the jar of pickles because they don't have the strength. And they're like, what's happened? That's an estrogen effect. Because when you look at how estrogen affects skeletal muscle and the feedback mechanism for strength and power development, it's in every part. It's on the satellite cell to develop more muscle fibers. It's on the nerve endings to be able to say, yep, let's create a really fast nerve conduction across the gap junction to be able to fire a lot of fibers to create a strong contraction. And it's also part of the contractile proteins itself to be able to grab together to create a strong contraction. And it's also part of the contractile proteins itself to be able to grab together to create a strong contraction.

So when you lose estrogen, you're losing the impetus for those three main points of strength and lean mass development. So when I start explaining this, people are like, shit, now what do I do? It's like, okay, well, now we want to look at a nervous system response. Because if we can find an external stress that's going to create the same cascade feedback mechanisms that estrogen did, then we can keep progressing. And that is strength training. But it's not lightweight, going to failure type stuff. We have to take a page out of the power based work where we're looking at zero to six reps. We're doing heavy loads. We have lots of recovery between those loads

because we're trying to really stimulate the central nervous system and peripheral nervous system to say, you know what, I've got to have a lot of muscle fibers and I need to be able to recruit them quickly to have a very strong contraction to withstand that stress and load. So now we can build lean mass strength and power without estrogen. So when we're looking at perimenopause we have to look at all the systems that are being affected and we have to look at that external stress to apply to the body to create the adaptations that we

want. So when we look at it it's all about the intensity and the quality of the work it's not about volume. So like I said earlier, we're zone two is not really appropriate for women. At this point, it doesn't really do much for women at all. Because when you take away our sex hormones, we're really endurance. We're really fatigue resistant. We burn a lot of fat. So we have to look at how do we polarize it. We want to do some true high intensity work.

So that's 30 seconds or less, as fast and hard as you can go with two to three minutes recovery to have full recovery to be able to do it again. Might do that two or three times, or we do true high intensity interval training. And that is a little bit lower intensity and a little bit longer, but you're still really polarizing where when you go to do your interval, you're doing it at the intensity you're supposed to, and the recovery, you're fully recovering so that you can hit that intensity again. So the three big things there are proper strength training

and the intensity of your sprint or high intensity work. So like I said, it's not a lot of volume, it's the quality because each one of those factors affects the body in a way that will cause positive change. So strength, like I said, you know, you're going to get that central nervous system response to build bone and muscle. When we're looking at that high intensity interval training, which is not full intensity, but maybe 80%, this causes more of a cardiovascular and a blood glucose improvement. And then when we're doing that high,

high intensity sprint interval work, it causes a cascade of what we call myokines. So these are little hormone and feedback molecules that go from the skeletal muscle to the liver and the storage area of body fat and says, you know what, we don't need to store body fat. We don't need to take these circulating fatty acids and make them visceral fat. We need to use them and store them in really active tissue. So the aspect of doing those three things

is the mainstay during perimenopause is to benefit body composition, our metabolic health, our cardiovascular health, and then most importantly, our brain health. Because if we're doing strength training and creating neural pathway plasticity, we're doing lactate training to improve brain metabolism, then again we are able to support the brain when it is starting to lose the receptor sensitivity of estrogen progesterone because we don't have those sex hormones anymore.