[Stacy Sims] (0:00 - 0:36)
When we look at cardiovascular training, which is obviously really important, aerobic training as well and anaerobic, there's lots of research for example that's put out now around the Norwegian 4x4 being a really effective way to train your VO2 max or doing like one minute sprints on and off and oscillating. None of these workouts actually take very long because even the Norwegian 4x4 is like 28 minutes I think because it's four minutes on three minutes off and it's pretty intense. What would you say here for women like where should our focus be and does that research hold its own in relation to women?

[Angela Foster] (0:37 - 2:42)
Those are all typical high intensity interval training sessions. Those are true high intensity interval training sessions. People think they're new and novel because they're just now hitting the mainstream.

They've been around high performance sport forever and when you're thinking about what is high performance sport versus the general pop, general pop thinks that high intensity is a spin class or a very boot camp right and that's what they're used to with high intensity. So then when you come out and go look if we're doing a really hard workout that's a true high intensity session like the Norwegian 4x4, this comes stock standard out of endurance racing and high performance. It's all about being able to build lactate tolerance and build that top in VO2.

Same with one minute on one minute off. It's a very short amount of time but that still fits into high intensity interval training. Neither one of those fit into sprint interval training which is that subset but they are true high intensity interval training sessions and they're very beneficial because they do help with lactate production.

They do help with building that top end aerobic capacity or VO2 and again it's about moving well with muscle economy and building muscle that's going to help as a glucose sink that helps with insulin resistance right. So we're thinking about all the forward things that are going to help with longevity and the more the research is coming out it's still all pointing to short sharp. We want to look at how we're perturbing the body so we have a really strong stress and it recovers from it through resistance training and the different modalities of resistance training through the cardiovascular work and we were doing comparison and literature between low intensity and high intensity with cognition and brain health and when we're looking it's like yeah well people always are always saying that the low intensity aerobic exercise helps with BDNF. Sure it's a miracle grow but what you also need is to plant the seed.

So if you get miracle grow and the seed wouldn't you pick that so that you can actually grow the neural network that you want that comes with high intensity work and strength training. So there's always like nuances within the literature of what we should be doing.

[Stacy Sims] (2:42 - 2:46)
So we actually need both is what you're saying.

[Angela Foster] (2:46 - 2:52)
If you're short on time though you still get BDNF and the neural changes with the high intensity.

[Stacy Sims] (2:53 - 2:55)
Yeah and with things like squats right.

[Angela Foster] (2:55 - 2:56)
Yep exactly.

[Stacy Sims] (2:57 - 3:31)
Yeah yeah so actually prioritising this if you're short on time prioritising the resistance work and the high intensity uh first and then you can use that zone two for recovery like as you know soul food yeah exactly yeah yeah and also improves blood flow right you're going to recover faster from your lifts and things yeah yeah um when you look at that you just made a distinction there between high intensity and sprint training sprints are much shorter uh and faster harder right they're all out a hundred kind of or super maximal.

[Angela Foster] (3:32 - 4:51)
Yes and they have longer recovery so people are like doesn't Tabata count i'm like no because you can't hit the intensity you need to in a Tabata session. Tabata you can put in high intensity work if you can move well enough to get your heart rate up really high in the 20 seconds but if we're thinking about sprint interval training it's as hard as you possibly can go for 20 to 30 seconds and you have at least two minute recovery in between and the recovery is bringing your heart rate down resetting central nervous system allowing your body to regenerate ATP so that you can hit that that sprint again as hard as you possibly can. So with sprint interval training it's as hard as you can with lots of recovery and you might only do two or three of those 20 to 30 seconds because that's all you can generate from a power perspective and maintain that intensity. When we're looking at the high intensity interval training the variability of the recovery is there for a metabolic play.

What I mean by that is when we're doing sprint interval that's more about that top end neural network trying to create epigenetic change from myokine responses. We're looking at high intensity interval training this is more working the metabolic aspect of let's build some lactate and really be able to clear it out as well as work the aerobic capacity at a higher level we're right at threshold that's going to help boost that vo2.

[Stacy Sims] (4:52 - 5:18)
So when we're looking at this if someone is trying to choose how many different workouts they're doing here right we could have these very short sharp sprints which I find just like bolt on really well to an upper body day because I haven't used my legs at all and it's very efficient. If I was doing something like that vo2 max style training right the Norwegian 4x4 or the sprints I most likely would do that as its own session.

[Angela Foster] (5:19 - 5:19)
Absolutely.

[Stacy Sims] (5:19 - 5:24)
Yeah because it involves quite a bit of recovery afterwards and I wouldn't do it after leg day.

[Angela Foster] (5:25 - 5:25)
No.

[Stacy Sims] (5:25 - 5:59)
That's when I see my HRV tank. It's not a good strategy. So if someone's looking at this and they're thinking okay hang on there's a lot of things here and there'll be some people who feel a bit overwhelmed and other people like me who just love exercising who are like I want to do it all and then they're going to be like on the floor.

How might they like if we look at across seven days I've seen you talk about we actually become more resilient and we manage our cortisol better when we do high intensity training so there's this misconception that if I'm struggling with stress I mustn't do it. How can we optimise for this Stacy?

[Angela Foster] (5:59 - 6:36)
I want everyone to think about quality over quantity because we've all come from the whole calories in calories out fat burning workouts the longer the better all that kind of stuff and we need just to reframe it and take away that mentality. You want to think about high quality low volume work so it could be three times a week where you're going to do two total body heavy strength compound days finishing with some sprint work so that could be battle ropes explosive kettlebell swings could be salt bike any kind of thing right it could be running up some stairs and that way you're getting uh four sessions done in two days.

[Stacy Sims] (6:37 - 6:42)
So this is where you're just putting a little bit of the actual proper sprint style stuff the 20 seconds or less.

[Angela Foster] (6:42 - 8:02)
Exactly at the comma sprint finisher or if you need a little bit more time to prime and warm up for your strength training session then often people will do it first at the start because a 10 minute sitting on a bike for 10 minutes to quote warm up for strength training session doesn't really do anything. If you really want to warm up and prime everything you got to get some sprint action in there get that heart rate up you can warm up a little bit then do your sprints and then get into your heavy lifting but you can also do it in the reverse because I know there are some days where Mike I can't face bringing my heart rate up really high but I can really get in there and lift heavy and then at the end I'm like yeah I've got a little bit more I'm going to do some battle ropes because I've just totally killed my my legs from leg day right so there's options there and then one other day of the week you're doing a true high intensity interval session so that would be your nordic four by fours so you end up with five sessions in three days or in three actually marked out times that you're going to the gym and then if you have the bandwidth and the ability to have some soul food time do it that's the thing about the zone two stuff it's not off limits it's just when we're prioritising when I think about quality over quantity and then any leftover stuff that's when you can play around a bit I think the other

[Stacy Sims] (8:02 - 8:40)
thing that's happened with zone two right is that it stopped being relaxing because everyone's become obsessed with the fact that they must be at the top of zone two and I know when I was interviewing Paul Lawson he was like do you know what even zone one counts it like it works really well for your endocrine health your immune system just get out there like go for a nature walk and enjoy it and I think that's just I don't know that just feels so freeing to not think that you have to go am I at the top do you know what I mean because you see all the bros with their weighted vests on and like am I right at the top and what's like 180 minus my age and I have I hit that and now it's actually not relaxing at all when you start to do that and they're never in zone two when they

[Angela Foster] (8:40 - 9:46)
do that because they are thinking they're at the top end but most of them are crossed over and it's too too hard because when we're looking at using a heart rate metric heart rate is like a whistle on a clipboard for a coach it's very variable there's so many different things that affect heart rate so it's better to go by rating of perceived exertion and I don't really think the public's been educated on what is true zone two I mean I'm laughing that there are wearable companies that have come out with zone one or zone zero it's like you're just living right it's like there's no such thing as zone zero there's nothing scientific about zone zero you call it a relaxed state and or you know just recovery so when you start mixing that in as well it really confuses people because they're like well I thought zone two was a just right above the the fast walking state yeah but now it's like no you got to push a little bit more and we have to do the top test now that's too hard so people need to dial it down because that's the problem is they get so focused on hitting these metrics because they've heard so much about it but they don't

[Stacy Sims] (9:46 - 10:17)
think they really know what those metrics are zone zero has really confused me because I saw that come up on my weep and it was quite new and I was like what is zone zero because like is that does that basically mean that I'm not moving um it also anything that's respawn I've found is a very kind of inaccurate way anyway because like if you're doing a sprint it won't even show the heart rate until you finished and then you're in recovery and you're like I don't even know if I'm recovering quickly enough do you know what I mean it doesn't I find that if I'm looking at heart rate it has to

[Angela Foster] (10:17 - 12:05)
be with a chest strap absolutely I mean like if I get on the watt bike and do a Zwift workout it never ever pegs the high intensity I only get on Zwift to do sprint workouts or high intensity work short sharp and it's at home so I don't have to worry about getting hit by a car if I'm not on my bike but it never registers never it always like oh that was a really nice recovery right I'm like what are you kidding I was pushing 230 watts for three minutes and those are my three minute intervals I'm like a top end so don't tell me that was recovery so when they come out with zone zero it's like what are you talking about there there's no scientific basis to be calling it zone zero it's all marketing it's to make people go oh okay I can spend some time at 50 or below and that's just living that's like getting up and moving around your day making breakfast for kids or yourself getting in and out of the car and they're just trying to quantify that daily existence but there is no exercise physiology science to show what a zone zero is the zones were designed to be able to quantify workload during exercise sessions to be able to say okay we want your heart rate to be 50 or less so we're going to call that zone one so that you know what recovery is we want you to hit the top end of your metrics to work on vo2 in a colour coding we're calling in that zone um five or six so that's at your top end of your heart rate but it's all about being able to rate according to heart rate and rating perceived exertion to quantify training loads it's not about quantifying what's on your wearable so I find it again this is where marketing is trumping science and people are really buying into it it's like it's just living it's just your daily life you don't need to quantify it yeah it's interesting

[Stacy Sims] (12:05 - 13:01)
because there's also a new thing that's come up which is your biological age which I can't see any kind of basis for because it's just on a wristball measurement and it starts to basically rate me according to movement even though for example I might have had I might have been working and podcasting and doing things that are more sedentary but then I might have done a really intense workout but it will then downgrade me because today I didn't quite make the steps but then when I look at as in when I say the steps the ones that I normally make right which tend to be 12 000 plus but when I look at the longevity science it seems most of the benefits come in around 8 000 steps anyway so I find it super confusing because I think people who maybe don't have any training in this area will be looking at it and going oh my god my age is going up I'm gonna I have to get out more and I have to do this but they're not necessarily actually like putting their physiological strain on the system in the way that you're talking about that drives a benefit

[Angela Foster] (13:02 - 13:43)
correct and the other thing about steps is the 10 000 steps it comes from a marketing campaign in the 1960s so people are always like I gotta get my 10 000 steps like yes movement is great any incidental movement is great but you don't have to target a certain amount of steps because I'll have women who go oh how many steps should I get in addition to all the training I'm doing I do I have to go out at the end of the day and try to get an extra 5 000 steps I'm like no what are you talking about the steps are there to make sure that you are incidentally moving throughout the day so you're sitting you're sitting you're standing you're walking around you're parking far away from where you need to go and then you can have focused training but if you're so obsessed with numbers from wearables you're missing the mark and that's the part that's frustrating

Most of us have heard that we need to exercise more, but today, exercise physiologist Dr Stacy Sims digs into what kind of training actually moves the needle for women — and why longer, slower workouts may be leaving results on the table.

We get into the real difference between high-intensity interval training and sprint interval training, why the Norwegian 4x4 is one of the most efficient tools for building VO2 max, how to structure a full week of training across just three days, and why your wearable's heart rate zones are probably misleading you more than helping you.

WHAT YOU'LL LEARN

Why high-intensity and sprint interval training are not the same thing — and why the distinction matters
What the Norwegian 4x4 actually is and why it's so effective for VO2 max
How to combine strength, sprint, and cardio work into just three sessions a week
Why resistance training and high-intensity work should be prioritised over Zone 2 if you're short on time
The truth about BDNF, brain health, and why you need both a seed and the miracle grow
Why wrist-worn heart rate monitors consistently fail during high-intensity efforts
What Zone 2 actually is — and why most people are training too hard to be in it
Why 10,000 steps is a marketing figure, not a science target
Why "Zone Zero" has no basis in exercise physiology