00:06
Hey everyone, it's Mikki here. You're listening to Mini Mikkipedia. And today I wanna chat about the Zone 2 training for females. And there's been a lot of talk on social media suggesting that women shouldn't do Zone 2 training as part of their overall exercise program. There are a number of reasons provided for this, including sex-based differences in fiber types, mitochondrial oxidative capacity, inherent metabolic differences,

00:35
and exercise related changes in lactate transporters. And this is particularly with regards to women in the perimenopause and post-menopause age groups. However, this isn't designed for females who train for endurance, as I understand it. I think this is just in general to the wider female athletic population. And Peter Attea wrote an article about zone two training.

01:04
in it. He did a great job of critiquing these claims. And I wanted to summarize a little bit of what he said, plus also add my own thoughts on it based on what I know about Zone 2 training, metabolic flexibility, and just females in general. First though, what is Zone 2? Zone 2 is a moderate intensity aerobic exercise where you can comfortably maintain a conversation, but probably not sing.

01:31
and it typically keeps your heart rate between 60 to 7% of your maximum heart rate, making it an effective way to improve fat metabolism and endurance. Now, those of you familiar with Phil Maffetone's work, and I've had Phil on the podcast a couple of times, will remember that his formula is another way to determine your zone two, which is 180 minus your age and...

01:59
Unless you have something wrong with you, or you are incredibly fit, that is, I guess, the number with which you should try to keep your heart rate under or around in order to maximize your zone two fitness and capacity. And you build on that as you go along. And there's a lot of research to show that this practice helps improve mitochondrial

02:29
their capacity to produce energy. So you'd think that that would be a good thing for everyone. However, the reasons I just mentioned about differences in fiber types, etc., have led to some to suggest that zone 2 should not be a priority for women. And one of the reasons given is that women typically have a higher proportion of slow twitch type 1 muscle fibers compared to men. And these fibers rely mainly on mitochondrial respiration for energy

02:58
contained significantly more mitochondria than the fast-twitch type 2 fibers, which depend more on glycolysis, which is converting glucose to lactate or pyruvate for energy. Now there was a meta-analysis conducted, which is looking at the results of all studies in this area, and there were 110 studies in this paper which examined muscle fiber type and size in people aged 18 to 59 years.

03:25
and that did indeed find that there were differences between men and women, both the size and distribution of muscle fibre types. Women had around 2.6% more type 1 fibres on average, so they had 53.2% compared to men having 50.6%. And men also had around 2% more type 2 fibres across all subtypes. So there are sex-based differences. However

03:53
these differences were no longer seen above the age of 60 years. So it doesn't make for a relevant argument against zone 2 training to suggest that women postmenopause do not benefit from doing it because these differences had completely disappeared. In addition to that, if the difference that I mentioned to you seems small, I tend to agree. And particularly as these fiber types aren't the only fibers present, as people have what is known as hybrid fiber types.

04:22
which can account for about 20 to 40% of fibers present. And these can actually transform based on the type of training that is undertaking. So endurance training amplifies the type one fibers, which is the type of fibers that women predominant in, and reduce type two fibers, which are the strength and power training fibers. And this shift accounts for anywhere from four to 17% of fiber type distribution.

04:49
and is more significant than the difference seen based on sex alone. It is also unclear whether the differences in the fibre types come from these inherent differences in training modalities because women generally engage in more endurance-based activity compared to power-based activity also. So some of the differences we see in those fibre types might well be due to these hybrid fibres shifting from those type 2 to type 1.

05:17
one muscle fiber types rather than that they were inherently present in the first place. So the argument that there are sex-based differences in muscle fiber types and women shouldn't need to worry about doing zone two training doesn't really hold up under these conditions. A second critique refers to what we find in research that women typically use more glucose during and after meals and oxidize more fat during exercise, which leads to that conclusion that they are more metabolically flexible.

05:46
This metabolically flexible status though is dependent on a few factors which don't seem to be acknowledged when this argument is made. There is age, a poor diet, high stress level, and physical inactivity all impact on the ability to burn more fat and less sugar, especially in an exercise setting where it is desirable to be doing so. And if we consider that over two thirds of the adult population

06:13
are classified as carrying excess body fat, placing them at increased health risk, and only 7% of the population have all biomarkers that would determine an individual is metabolically healthy. I just think it's a big call to say that women are more metabolically flexible than men. Women may have been born this way, but it isn't a given that they remain this way. And so all of those factors that I just mentioned, like diet and like activity level, fitness level, et cetera.

06:42
all determine how metabolically flexible someone is, and you just don't remain metabolically flexible across your lifespan just because of your biological sex. In addition to that, studies looking at post-menopausal women show that they are less metabolically flexible compared to women of reproductive age. So we don't hold that same metabolic flexibility regardless of our age either. And as I mentioned, baseline fitness also impacts on metabolic flexibility.

07:12
and those that are less fit are less able to utilise fatty acids as a fuel source. So for all of these reasons, choosing to do an activity that helps enhance metabolic flexibility such as zone 2 training just makes sense to my mind and it isn't something that we need to sort of throw off the table for women. In addition to those other points, cross-sectional studies have shown a higher prevalence of impaired fasting glucose and diabetes in men compared to women.

07:42
Most studies focus on healthy women of reproductive age. And during perimenopause, when estrogen fluctuates, inflammation increases, and sympathetic nervous system response is an almost permanent state in some, the stress hormone elevation increases the likelihood of insulin resistance. When estrogen drops at the onset of menopause, it does also negatively impact on glucose handling. Engaging in zone two training

08:11
improves mitochondrial oxidative capacity, which leads to a more efficient fuel utilization, lowers blood glucose levels, reduces insulin requirements, and leads to an overall better metabolic health. So this collectively contributes to reduced insulin resistance and better management of glucose, thus improving metabolic flexibility. And all of these things are important for everyone as we age. And of course,

08:41
particularly women, as we are much more prone to insulin resistance with the onset of menopause and that drop in estrogen. So anything you can do to support it, I think just makes a whole lot of sense. Now, when we look at sort of changes in metabolic flexibility with training, we see that in studies of younger adults, there are differences that exist between men and women. Yet zone two exercise has been found to improve in both groups regardless of the starting point.

09:09
So there are studies that shows, such as one which I mentioned in my email this morning, that men's fat oxidation improved from 19 to 24%, while women's improved from 34 to 41%. So women started off at a higher level, but still gained a similar improvement. And these improvements were attributed to both increased number and size of mitochondria, thus enhancing their energy production, and a greater use of fat as a fuel source.

09:38
with more intramuscular triglycerides able to be used as fuel. So whilst a woman may start with a higher fat oxidation level, we can definitely see significant improvements with training. And the more metabolically flexible you are, the easier it is to hold on to this with age. So just because women might be better than men at this doesn't mean that they don't want to improve it. I mean, surely improvement in your metabolic status is only going to be a good thing regardless of how high it might be to begin with.

10:07
And a related argument to this focuses on differences in mitochondrial quality. And there's been studies suggesting that women have a higher mitochondrial respiration than men when matched for VO2 max. However, when they actually normalized the numbers based on total mitochondrial protein concentration, so the number of mitochondria, there was actually no difference. They were nearly equivalent. And it does suggest that aerobic capacity is achieved differently.

10:36
women might have more efficient mitochondria, while men might have more mitochondrial mass. Upon saying that though, other studies that have looked more broadly think that really it's the jury is actually out with these biological sex differences in total. And that studies looking at this have been performed in young and fit individuals and these may not hold with people of lower fitness levels or who are of an older age group. So I think there's a lot of

11:04
mechanistic and sort of baseline physiology that is talked about in this space, but not all of it holds up when you sort of scrutinize it, looking at age, looking at fitness levels, and also just what we don't know in this area. So while there's a lot of physiology and potential mechanistic reasons why women should be more metabolically flexible and therefore maybe they don't really need zone two training.

11:33
that just doesn't hold up when you critique the physiology, particularly with those differences in age and fitness levels when they come into play. Another point I think is worth mentioning is that trying to get women to move away from exercise they really love could end up impacting them negatively in the long run. Exercise like group fitness classes, running in the gray zone, which is my particular favorite, spin bike sessions done at a higher intensity,

12:01
They might add a physical stress and reduce optimal muscular and metabolic adaptations. But let's just look at the big picture. You're active. And over half of the adult population in New Zealand do not meet those physical activity guidelines. And if I'm going to be blunt, these aren't overly hard to meet. So honestly, any activity is better than no activity at all.

12:25
And women in the perimenopause and menopause age group are less likely to be active than at other times of their life due to competing responsibilities, looking after households, looking after children and parents, trying to have a career at the same time. But things like exercise often get left to last. This is not the case for everyone, but oftentimes women put themselves last. So to then say to them, no, no, the exercise that you...

12:53
want to be doing, that's not good for you, you should be doing this, I think is just throwing the baby out with the bathwater. The last message that they need to hear is that the thing they love is no longer good for them. So like I say, any activity is good and more attention needs to be paid to this as too many are so blasé about it, thinking that their body size defines their metabolic and cardiovascular health. And it really doesn't. However,

13:20
Even if you are like me and you love the gray zone running and you love the high intensity training that should really be doing us in, it is super important to make time for recovery from the training because we do want to be able to absorb the physical stress from activity and we should make time for strength training. I just used the word should. I'm sorry about that, but it is true if you aren't already because all of these elements are important for fitness and longevity. I would argue that rather than avoiding it.

13:50
Starting out looking at zone two and actually doing that type of training is probably necessary for anyone embarking on an exercise program to help build that resiliency and fitness. There are studies that show that increased blood flow to the muscles from aerobic training then allows for better adaptations when strength training is introduced. So if someone listening to this is new to activity in general, starting at that zone two and then embarking on strength-based training,

14:18
I think just makes a lot of sense. And being healthy and fit as we age requires so much more than just strength training and sprint or high intensity intervals. And I think it absolutely should include zone two training. In addition to that though, it is about engaging in many modalities of training to ensure that mitochondrial health, blood sugar regulation, reduced oxidative stress, reduced inflammation, and improved emotional and cognitive health. And I don't think that

14:47
we should ignore zone two training if we wanna optimize our health span over the lifetime actually. So everyone's got an opinion, right? And that is my opinion. If you love zone two training, I think you should just continue to do it. And if you're not doing it, I really do think that maybe you should just add it in. All right, team, let me know what you think. You can find me on Instagram, Twitter and threads @mikkiwilliden, Facebook @mikkiwillidenNutrition.

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or head to my website mikkiwilliden.com book a one-on-one call with me. All right guys, have the best week.