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1. Dr. Stacy Sims on PRE-MENOPAUSE

2.  Dr. Stacy Sims on PERI-MENOPAUSE:

  • Changes in ratio of Estrogen and Progesterone impacts all systems of the body
    • Microbiome changes
    • Recovery
    • Body Composition
    • Brain +Neurotransmitters
    • Sleep architechture
  • Hormones changing – now I need to find an external stress that is going to cause an ADAPTATION the way the hormones used to support
  • Polarize high intensity training and heavy lifting
  • Dropping the volume and adequate recovery
  • Creating a stress to stimulate growth hormone
  • Epigenetic changes in muscle to help with blood glucose control and glucose homeostasis
  • Signal central nervous system to maintain power, speed and lean mass

3.  Dr. Stacy Sims on POST MENOPAUSE:

Early menopause – 5 to 6 years after the one day in time of MENOPAUSE

  • Lift heavy
  • Sprint interval training 2-3 x week
  • Limit or decrease lower intensity exercise with high volume (less is more)

Late menopause- 6 years after the one day in time MENOPAUSE

We don’t respond as well to the high intensity work 

  • Solution – more regular doses of sprint intervals but not more volume- shorter doses
  • SIT 4 days of 15 minute intervals
  • We lost sensitivity to estrogen or progesterone without the receptors around
  • To keep lean mass, blood pressure in check, vascular, bone strength, cognition, and proprioception
  • More play early post menopause but later post menopause we need to do SIT daily but short dose.
  • more; regular, shorter doses of SPRINM interval training as we have lost sensitivity and loss of receptors
  • Example 4 x 20 second sprints instead of 10 … upper intensity focus

Sprint Interval Training 

  • Central nervous system response – fast muscle contraction, neural pathways and avoid cognitive decline
  • Glycolytic fuel- ATP CP and carbohydrate use for fueling
  • More GLUT4 transporters- gate to allow glucose to come into cell without insulin = maintain glucose homeostasis as we are more insulin resistant as we age
  • Cross talk with exerkines – deep abdominal fat and skeletal muscle via messengers – need carb in the muscle and not deep ab fat
  • Proprioception – fall risk decreases
  • Not the long slow distance endurance training
  • Push RPE 9/10 and no more than 30 seconds, recovery back to Zone 1
  • Fast Twitch muscle fibers

Zone Two for women?

  • Research is based on male studies
  • Women already have a larger amount of slow twitch fiber- oxidize fat better
  • Women have less fast twitch muscle fibers than men
  • Born XX – greater mitochondria density, mitochondrial respiration and greater sensitivity to metabolites that inhibits free fatty acids that come into cell
  • Women are already very good at taking lactate, recycling it to use as fuel in aerobic metabolism
  • Benefits of ZONE TWO– mitochondria health, increasing oxidative capacity, increasing mitochondrial health, increasing the number of MCT1 Transport Proteins
  • MCT1 Transport proteins take lactate out of circulation then put them into mitochondria to get the lactate into circulation and be used as fuel
  • MEN do need to increase the MCT1 to increase mitochondria health, mitochondrial respiratory capacity and slow twitch muscle fiber
  • MCT1 – put lactate into circulation and out to use as fuel
  • Men don’t have the same response as women do = difference between the exercise intensity = women need to do more high intensity work as they have less glycolytic muscles = we need to stimulate lactate production and regulate the ability to produce it then clear it
  • if women don’t improve by doing sprint training -and spend too much time in Zone 2 ‘long slow distance’ – stuck being slow
  • Men need more Zone Two training than women
  • The exercise intensity – women need more HIIT as less glycolytic muscles or stuck in slow pace
  • Sprint work and HIIT in women vs. men = women upregulate more MC1
  • The exercise intensities- women need more HIGH intensity to stimulate lactate, to produce it and clear it …less SLOW MO workouts than what men need
  • Women need to change how they fuel and train to get their desired improvements


Dr. Stacy Sims on Women and Zone 2

Zone 2 training is a hot topic, but like many things, it’s different for females.

If you even remotely follow fitness and training media, you will have seen the buzz around “Zone 2 training”–generally known as steady, conversationally-paced exercise–and how it is the golden child of endurance (and health) training programs. And while there’s no doubt that easy days have an important place in health, fitness, and training, for women specifically, the benefits are being oversold.

When we talk about “zone training”, we mean breaking down our training intensities into heart rate or power ranges that are used to form a structured training plan or workout.

The purpose of stratifying intensities in this way is to achieve specific physiological and metabolic adaptations through our training.

In this structure, Zone 2 is relatively easy and long (60 to 70% of max for 45+ min) and you should feel like you can go for hours.

The current recommendation is to have the bulk of your exercise sessions–three to four training sessions a week–be in Zone 2.

Why the emphasis on Zone 2?

The thought is that Zone 2 is a low enough intensity to stimulate mitochondrial and other adaptations within the muscle cell that

improve the skeletal muscle’s ability to use fat as a fuel, spare carbohydrate;

improve metabolic flexibility (the ability to rapidly switch between fat and carbohydrate oxidation)

as well as to better clear lactate during higher intensity exercise. 

Female Muscle Makeup & Zone 2 Training

To understand what this all means for female athletes, let’s dig into how this works within our specific muscle fibers.

We have two primary types of muscle fibers: Type 1 fibers, called “slow twitch” fibers, and Type 2 fibers, called “fast twitch” fibers (which are broken down into subtypes Type IIa and Type IIb).

Type 1 fibers have the greatest mitochondrial density (mitochondria are the “powerhouses”of the cell) and are highly oxidative, meaning they are very efficient at using fat as a fuel.

As intensity heats up and muscle contractile speed increases, we need more energy than Type 1 fibers can generate using fat, so Type IIa and then Type IIb fibers are recruited.

Type II fibers have lower mitochondrial density and high capacity to use glucose for energy.  

Because Type I fibers are so efficient at using fat as a fuel to keep going, the concept around Zone 2 training is that by spending more time tapping into Type I fibers, we can increase their mitochondria density and respiratory rates (the metabolic reactions that require oxygen to convert fatty acids into the usable ATP)

…as well as increasing the transport proteins (MCT-1) needed to clear lactate quickly and efficiently (during exercise, lactate is produced by the Type II fibers, but primarily cleared by Type 1).

Sounds great, doesn’t it?

Go long and easy to boost your metabolic health, endurance capacity, and improve your overall performance!

But, hold on a minute.

If the main goal of Zone 2 training is to increase the number and functionality of mitochondria within the skeletal muscle, and increase fatty acid utilization, we need to question the validity of this concept for women.

Yes, you’ve got it.

This conversation around Zone 2 benefits does not take into account sex differences.

Research shows that females (e.g. XX chromosomes), have more oxidative (Type 1) fibers, have greater fatigue-resistant muscles, have greater autophagy activity and a higher reliance on lipid (fat) metabolism as compared to males(e.g. XY chromosomes).

We know that training status does have an impact on muscle mitochondria adaptations (basically increasing muscle oxidative capacity), but when we look at equivalently trained women and men, we see that there are differences, specific to skeletal muscle, in mitochondrial oxidative functional capacity.

Women have approximately one-third greater mitochondrial intrinsic respiratory rates (the amount of mitochondrial respiration occurring for a given amount of mitochondrial protein) and greater mitochondrial oxygen affinity (p50mito) than men.

What about increasing fatty acid utilization then?

Should women spend time in Zone 2 to increase their ability to use fat?

Again, no.

Research shows, as compared to similarly trained men…

women have a greater amount of intramyocellular lipid droplets (aka, fat particles stored in skeletal muscle cells),

a greater amount of the plasma membrane fatty acid transporter protein CD36 which increase fatty acid uptake into the cell, and also

a greater sensitivity to malonyl-CoA (M-CoA) (a metabolite that can inhibit fatty acids getting into the mitochondria), 

What about metabolic flexibility?

Women are already metabolically flexible!

Not only do women oxidize more fat and less carbohydrate during prolonged exercise; women also have greater metabolic flexibility because there is a greater ability to switch between fatty acid and glucose use,depending on what nutrients are available.

Finally, when it comes to improved lactate clearance, it may be more important for men to improve their clearance capacity. We see that men exhibit greater MCT-4 and MCT-1.

For one, because they have a greater ratio of Type II to Type 1 fibers (remember type II is glycolytic, which produces lactate); men rely more on carbohydrate metabolism than fat metabolism during exercise, and they have higher circulating plasma lactate levels per unit of workload (fitness matched to women).

When it comes to endurance training, men upregulate MCT-1 more so than women, which may look like a bad thing, but in the big picture, it makes sense with respect to sex differences in glycolytic fibers and circulating lactate during exercise.

Should women be concerned about a reduced expression of MCT-1?

The short answer is no.

Because women’s bodies fuel exercise differently than men, although we do produce lactate, because we have less overall glycolytic activity, we will have less overall expression of MCT-1.

When women do a block of specific high intensity work, and up regulate MCT-4 (the transporters that pull lactate out of cells) there is also a response to upregulate MCT-1 (to clear the lactate). 

Where does all this leave women in the Zone 2 conversation?

For women, Zone 2 training is great for active recovery, a certain amount of base building for endurance athletes, and social exercise.

Yes, there is merit in Zone 2 BUT if you are planning the bulk of your exercise time for Zone 2 training to enhance mitochondria function and fatty acid utilization, you may want to revisit that concept (more on that in a future post).

One final and very important point is that when you do train in Zone 2, really make it Zone 2.

This is really one of the biggest problems I see:

women spending too much time going hard or “kind of hard” and not enough time going truly easy.

When Zone 2 training enters the conversation, they think they need to spend hours doing this, but it very often becomes hours doing moderate intensity that is harder than Zone 2 and is eventually counterproductive in that it just makes them worn out without the training gains.

The popular zone 2 protocol doesn’t work the same way for women. Here’s what to do instead.

In my last blog, I reviewed down to the cellular level, why zone 2 training, which is currently being promoted across the internet as the priority training for health, longevity, and performance, isn’t as effective for women as it is for men. Now let’s talk about what type of training scheme delivers those benefits best for females.

First a very quick review:

  • Zone 2 is relatively easy and long (60 to 70% of max for 45+ min) and you should feel like you can go for hours.
  • The current recommendation is to have the bulk of your exercise sessions–three to four training sessions a week–be in Zone 2.
  • The theory is that Zone 2 is a low enough intensity to stimulate mitochondrial and other adaptations within the muscle cell that improve the skeletal muscle’s ability to use fat as a fuel, spare carbohydrate; improve metabolic flexibility (the ability to rapidly switch between fat and carbohydrate oxidation), as well as to better clear lactate during higher intensity exercise.

As reviewed in that last blog, putting a precedence on zone 2 training in women may not be the ideal way to improve skeletal muscle mitochondria function (to include increasing mitochondria expression, improving fatty acid uptake, and improving lactate clearance).

If you want to follow me further into the rabbit hole for a moment, I have discovered additional compelling data regarding exercise intensity’s impact on MCT1 and MCT4 expression that should make women rethink their training priorities and why.

First, let’s review what MCTs are.

MCT stands for “MonoCarboxylate Transporter”.

  • Basically, they are proton-shuttling proteins that are found in many tissues of the body.
  • For our purposes here, we’ll talk about MCT1 and MCT4, which are specific to muscle (skeletal and cardiac) and their ability to transfer lactate and pyruvate across the plasma membrane.
  • During heavy exercise, the high energy demand of your contracting skeletal muscles trigger an increase in glycolysis; the breakdown of a glucose molecule into pyruvate and in anaerobic conditions, pyruvate becomes lactate.
  • Because we now know lactate is not a “waste” metabolite but can be pulled into the mitochondria of skeletal and heart muscles and used as fuel, exercise researchers are interested in how lactate shuttles across the cell membranes.
  • This is where MCT1 and MCT4 transport proteins come into play.
  • We see that MCT4 pulls lactate out of the cells, whereas MCT1 pulls it into the cells (as pyruvate) where it can then be oxidized in the mitochondria to produce energy for muscular work.

Research shows exercise alters MCT expression, which is the basis of the zone 2 conversation: to increase the number of MCT1 transport proteins, to improve lactate clearance and mitochondria oxidation; which, in theory, will improve performance.

However, we see there are sex differences in the expression of MCT1 and MCT4 based on intensity of exercise.

Regardless of intensity, MCT1 expression increases in males, but it appears sprint interval training, (e.g. 30s or less), increases MCT4 expression only after a series of training sessions have occurred (meaning that the increase in MCT4 expression happens later in a training block).

For women, low intensity training shows minimal increases in either MCT1 or MCT4 expression, but sprint interval training does increase MCT1 expression in women (regardless of the recovery between intervals).

The thought is that by increasing lactate within the cells, an upregulation of MCT1 occurs; but the increased lactate does not have a signaling effect on MCT4.

This may be due to the decreased glycolytic capacity of women as compared to men for similar workloads; and also the influence of estrogen on MCT1 expression.

Now, if you are still with me, after the heavy science, let’s look at the practical aspects of what kind of training a female should do.

  • From a health and longevity standpoint, the goal is not only to increase MCT1 and increase mitochondria respiration; but also increase glycolytic capacity for brain resilience (enhancing brain glycolysis can increase neuronal metabolic strength to sustain a better cognition and slow down or prevent the progression of Alzheimer’s disease ).
  • Research shows that a minimum of 3 days a week of HIIT and SIT intervals dramatically increases MCT1 expression over 6 weeks, and increases the formation of brain-derived lactate (improving glycolytic capacity in the brain).

From a performance perspective, HIIT and SIT are critical, not only to improve lactate production and clearance, but to also stimulate an increase in the fast twitch, Type II fiber cross-sectional area (size and function); of which female have significantly less as compared to the slow twitch Type I fibers.

Hello power and speed!

What About Endurance Athletes?

Now, I hear all of the endurance athletes out there saying “what about the long slow training I need to do for my long-distance race?!”.  I am not saying it is pointless to do this kind of training, not at all!

You need it to have the strength and capacity to go long.

What I am saying is that to spend a significant amount of time in the low intensity/Zone 2 training does not enhance mitochondrial respiration or oxidative capacity like it does for men.

In fact, I love this quote from an article from the Journal of Physiology , “physical activity is essential for males to maintain mitochondrial integrity in conjunction with more coupled respiration like females, even though their bioenergetic capacities may remain lower than females…”.

Translation:because females have better mitochondria respiration and mitochondria density than men, men need to do the long slow aerobic work to be more like women (go figure…!).

By peppering your long slow work with specific high intensity work, you will improve your mitochondria capacity and anaerobic capacity by the nature of the high intensity work.

If you’re not an endurance athlete, I hope this helps clear up some of the confusion around the zone 2 messaging.

Remember, just because it is making the rounds in popular media, does not mean a full, deep dive into the literature to look at both male and female physiology has been done.

This may be a perfect example of why the tagline Women Are Not Small Men comes into play- male data has been generalized to everyone without really looking at the viability for positive outcomes.


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