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

Summary

Habits and Hustle: Episode 464 Summary

Episode Title:
Dr. Stacy Sims: Why Women Are Not Small Men and Need to Train Completely Differently

Release Date:
July 4, 2025

Hosts:
Jennifer Cohen and Habit Nest

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Introduction

In Episode 464 of Habits and Hustle, host Jennifer Cohen welcomes Dr. Stacy Sims, a renowned exercise physiologist and nutrition scientist, to discuss the crucial differences in training and health strategies between men and women. Dr. Sims delves into the unique physiological and biomechanical needs of women, emphasizing why conventional male-centric training protocols often fall short for female athletes and everyday women striving for optimal health and performance.

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1. Understanding Sex Differences in Physiology

Dr. Stacy Sims begins the conversation by highlighting the fundamental physiological differences between men and women. She explains that at birth, females (XX) and males (XY) exhibit distinct muscle fiber compositions:

• Females (XX): Predominantly possess more slow-twitch, oxidative, aerobic muscle fibers, enhanced with mitochondria. This composition supports endurance and the ability to utilize fatty acids and oxygen efficiently for sustained, low-intensity activities.

• Males (XY): Typically have a higher proportion of fast-twitch, glycolytic muscle fibers, optimized for speed, quick reactions, and high-intensity efforts. However, males often need to develop their aerobic systems further to match endurance capabilities.

Notable Quote:
“At birth, females have more endurance-type fibers, with a lot of mitochondria, allowing them to take fatty acids and use oxygen efficiently.” — Dr. Stacy Sims [01:56]

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2. Impact of Hormones and Puberty on Women's Biomechanics

As girls reach puberty, hormonal changes, particularly in estrogen and progesterone levels, lead to significant biomechanical transformations:

• Biomechanical Shifts: The center of gravity moves from the chest to the hips, shoulders and hips widen, altering posture and movement mechanics.

• Unaddressed Training Needs: Despite these changes, training programs rarely adapt to teach women how to move with their new biomechanics. This oversight contributes to feelings of awkwardness and increased injury risk.

Notable Quote:
“With these changes, women often feel ungainly because they aren’t taught how to run, jump, swing, or land properly.” — Dr. Stacy Sims [02:45]

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3. Common Injuries in Women: ACL Tears, Frozen Shoulder, and Plantar Fasciitis

Dr. Sims identifies several injuries that women are more prone to due to their unique biomechanics and hormonal fluctuations:

• ACL Injuries: Women are more susceptible to anterior cruciate ligament (ACL) tears because their quad-dominant posture and weaker hamstring strength make cutting motions riskier.

• Frozen Shoulder and Plantar Fasciitis:

  • Frozen Shoulder: Caused by a wider shoulder girdle combined with improper training techniques, leading to limited shoulder mobility.
  • Plantar Fasciitis: More prevalent in women during midlife due to changes in ligament strength and muscle contractions.

Notable Quote:
“We see a greater predisposition to ACL injuries because women don’t have the hamstring strength to counteract those cutting motions.” — Dr. Stacy Sims [05:49]

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4. Training Strategies to Mitigate Injury Risks

To address these injury risks, Dr. Sims advocates for tailored training approaches focusing on strengthening the posterior chain and improving muscle balance.

a. Developing the Posterior Chain

Emphasizing exercises that target the glutes and hamstrings can balance the quad dominance, enhancing overall stability and reducing injury risk.

• Key Exercises:
  • Deadlifts
  • Romanian Deadlifts
  • Hip Bridges
  • Hip Thrusts

Notable Quote:
“All the glute work, like deadlifts and hip thrusts, is essential for developing strong hips and reducing injury risk.” — Dr. Stacy Sims [10:36]

b. Specific Exercises for Shoulder Health

To prevent frozen shoulder, women should focus on strengthening the back muscles and improving shoulder mechanics:

• Recommended Practices:
  • Rhomboid exercises
  • Using back muscles during push-ups and pull-ups
  • Proper lifting techniques that involve dropping the traps and using the back rather than the shoulders

Notable Quote:
“If we use our back muscles to pick something up and extend through the hips, we reduce the load on our shoulders and lower the risk of soft tissue damage.” — Dr. Stacy Sims [09:52]

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5. Midlife Changes: Perimenopause and Training Adjustments

As women approach perimenopause, hormonal shifts further impact muscle and bone health. Dr. Sims explains the significance of adapting training routines to maintain strength and cognitive function.

a. Hormonal Effects on Muscle and Bone

• Estrogen Decline: Leads to reduced satellite cell activity, nerve conduction efficiency, and contractile protein integrity, resulting in decreased muscle strength and mass.

• Impact on Daily Function: Women may experience reduced strength, such as difficulty opening jars or performing everyday tasks, due to these hormonal changes.

Notable Quote:
“When we lose estrogen, we lose the impetus for muscle fiber development, nerve conduction, and strong contractions.” — Dr. Stacy Sims [16:04]

b. Training Recommendations for Perimenopausal Women

• Strength Training: Focus on heavy, low-repetition workouts to stimulate the central and peripheral nervous systems, promoting muscle mass and bone density.

• High-Intensity Interval Training (HIIT): Implement true high-intensity sprints with sufficient recovery to enhance cardiovascular health and brain metabolism.

• Prioritizing Quality Over Volume: Emphasize the intensity and effectiveness of workouts rather than the number of repetitions or volume.

Notable Quote:
“It’s all about the intensity and the quality of the work, not the volume.” — Dr. Stacy Sims [16:40]

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6. Navigating Information Overload: The Perimenopause Conversation

Dr. Sims addresses the confusion surrounding perimenopause, attributing it to the proliferation of misinformation and the tendency of experts to overstep their areas of expertise.

• Expert Siloing: Specialists often remain within their domains, leading to fragmented and sometimes contradictory advice for women.

• Need for Accurate Information: Emphasizes the importance of consulting the right experts, such as endocrinologists for hormone therapy, to receive tailored and accurate guidance.

Notable Quote:
“Those with the loudest microphones tend to not stay in their lane, causing more confusion for those seeking answers.” — Dr. Stacy Sims [14:06]

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7. Training and Nutritional Strategies for Perimenopause

To counteract the hormonal declines during perimenopause, Dr. Sims recommends specific training and nutritional strategies:

• Strength Training: Engage in heavy lifting with low reps to compensate for the loss of estrogen and maintain muscle mass.

• High-Intensity Interval Training (HIIT): Incorporate both true sprints and slightly lower intensity interval training to boost cardiovascular health and metabolic function.

• Balanced Nutrition: Ensure adequate protein intake and consider supplements that support muscle and bone health, although specific nutritional advice was beyond the scope of this conversation.

Notable Quote:
“We can build lean mass, strength, and power without estrogen by focusing on heavy strength training and high-intensity intervals.” — Dr. Stacy Sims [16:40]

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Conclusion: Key Takeaways

Dr. Stacy Sims underscores the importance of recognizing and addressing the unique physiological and biomechanical needs of women across different life stages. By tailoring training programs to focus on strength, the posterior chain, and high-intensity work, women can reduce injury risks, maintain muscle and bone health, and support overall longevity and cognitive function. Additionally, navigating the complexities of perimenopause requires accurate information and specialized guidance to effectively manage hormonal changes and their impact on health and performance.

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Notable Quotes Recap:

• “With these changes, women often feel ungainly because they aren’t taught how to run, jump, swing, or land properly.” — Dr. Stacy Sims [02:45]

• “We see a greater predisposition to ACL injuries because women don’t have the hamstring strength to counteract those cutting motions.” — Dr. Stacy Sims [05:49]

• “All the glute work, like deadlifts and hip thrusts, is essential for developing strong hips and reducing injury risk.” — Dr. Stacy Sims [10:36]

• “It’s all about the intensity and the quality of the work, not the volume.” — Dr. Stacy Sims [16:40]

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This episode of Habits and Hustle provides invaluable insights into how women can optimize their training and health routines by acknowledging and addressing their distinct physiological needs. Dr. Stacy Sims offers actionable strategies that empower women to achieve sustained health, performance, and longevity.

Transcript

[A]

Hi guys, it's Tony Robbins. You're listening to Habits and Hustle. Crush it.

[B]

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 episod, 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 Momentous. Momentous goes all in on NSF certification, which means every single batch is tested for heavy metals or harmful additives and label accuracy. And that's why they're trusted by all 32 NFL teams and top collegiate sports dietitians across the country. Here's the thing, they don't sell every supplement under the sun because they believe in nailing the basics with rock solid consistency. And those basics are protein and creatine, momentous sources. Creapure, the purest form of creatine monohydrate available and an absolute must for both men and women who want peak physical and cognitive performance. So if you're serious about leveling up, go to livemomentous.com and use code Jen for 20% off. Just act now. Start today. Jen for 20% off livemomentous.com.

[A]

I like to kind of start this conversation. 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 endurance type fibers. So your slight 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 in, 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 based 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 are not told about this. So we feel un gangly 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 impro 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 and we see this is really important in peri and postmenopausal, 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.

[B]

Biomechanics is a really big one right 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 proud, prone to injury wise or happen to women versus men because of our biomechanics. And then also how should we train for our biomechanics so women are more.

[A]

Quad dominant just the way our posture is in 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 and 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's put out for warmup, 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 ligamental 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 a 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 you 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. And it's, it's an inherent sex difference. Right. I can see you're like, you've probably experienced it.

[B]

I'm laughing, crying and laughing at the same time because I've had, I'm in my 40s, I had frozen. 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. I was like. I thought something was. I thought maybe I, like pulled a muscle in my shoulder. And the guy was like, no, you have frozen shoulder. And I'm like, what the hell's that? Like, how does someone get that? They're like, you're old, basically, is what he said 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.

[A]

Yeah. So frozen shoulder has to do with. We have a wider shoulder girdle because our hips have widened.

[B]

Yeah.

[A]

But if you think about all the metrics that we've taught to do, push ups, pull ups, they're all in a grip strength or. Or a grip width that's based on male data, male physiology. 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 in our 40s, we're like, okay, yeah, I really, I. 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.

[B]

So what should we be doing to offset that, that type of injury in the frozen shoulder? What is a good exercise to focus on?

[A]

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 pushup. 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 the whole onset of injury or soft tissue damage that can perpetuate injury.

[B]

And what about for ACL issues to kind of strengthen? What do you think is the best way to strengthen our posterior train our posterior chain?

[A]

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.

[B]

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[A]

Definitely. Yeah, absolutely. And it's, it's scary because the 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 want to know and we're going to unpack it for you.

[B]

Thank you. Because I think that's a great point because like I said, I see if you scroll on social media, every second post is about menopause and, or perimenopause. And I think the problem is there is so much noise and so much information. People are very confused. I know I'm confused. And I. Right. And I do this for a living. And I've had like all the, 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?

[A]

Exactly. Exactly. That's it. Yeah. And I'm finding that a lot of the. And I, 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, 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.

[B]

Right. I think that. I think there's so much confusion. So let's start with perimenopause. Right. Because it's before menopause. What, how, how should women be training, eating, recovering in that space for. For optimal results?

[A]

So as a physiologist, I'm going to explain what's happening on 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 anovulatory 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. 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, where 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 endurant, 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, you 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 is 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 as 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.