[Angela Foster] (0:15 - 0:31)
We talked about exercise, really important. And specifically, in your book, you talk about leg power. I've seen research that I put out on my Instagram on this.

Really interesting, right? The more powerful you are in your legs, the better protected your brain is. Why is that?

What's the link between the legs and the brain?

[Tommy Wood] (0:31 - 2:55)
There's a study that we did that looked at leg power and processing speed in older adults. This was using a database called NHANES here in the US. And what we looked at, which I think is important, is relative leg power.

So how strong are your legs relative to your body size, which is important, right? Because we shouldn't compare my legs' strength to your legs' strength, right? We're different people with different body sizes, different histories of training.

And that was actually the best predictor of processing speed in the brain, which does tend to decrease on average over time. So how powerful your legs were relative to you, right? So how strong you are for you was a very important predictor of processing speed.

There's probably a couple of reasons for this. One is that, again, having more powerful legs is an indication that you are doing things and going out in the world that are beneficial for the brain, including exercise. And another one is that when we work our legs, the more muscles we work, and the more we work them, we release a whole host of exokines, which people may have heard of, that then have a number of benefits, including for the brain.

So with resistance training, or strength training, or power training, this includes things like IGF-1. So IGF-1 is really critical for the structure and function of the white matter in the brain, which is the part of the brain that has lots of fat surrounding it, which insulates it and lets the neurones sort of do very fast processing and have fast connections. White matter and the changes in white matter with age are one of the best predictors actually of cognitive decline and dementia.

And in randomised controlled trials, if individuals are put on a resistance training programme, we see improvements in strength, we then also see improvements in white matter structure, white matter function, and cognitive function that comes along with that. So I think it's both the process of actually doing the work, right? We will call it a neuromuscular stimulus, right?

You're stimulating the connection between the brain and the body. And then the things that get released while you're doing that, probably both of those are going to be really important for brain function.

[Angela Foster] (2:55 - 3:35)
Interesting. So this is something that I've been playing around with, just as a bit of fun. I don't know if this is the way to measure it to see, but I'm playing around on my carol bike to see how much power can I produce, right?

And so when you do these sort of intense 20 second sprints in terms of re-hit, then it will register your peak power. Is that what we're looking at? The peak power in watts compared to my body weight?

So I think I got up to like, I don't know, I'm about 53 kilos, I got up to 700 watts. And I was really happy to cross the threshold because I've been in the 600s. Do you know what I mean for some time?

So that strikes me like, is that the ratio we're looking at? How much how much really what can I produce in relation to my body weight? Or how do we assess power?

[Tommy Wood] (3:36 - 4:55)
Yeah, the the data that we had for our study was, we call isokinetic leg strength. So it's, it's this weird, you know, like a leg extension or a knee extension machine that you do in the gym. It's a weird version of that, which I have done when I was a part of a couple of studies when I was an undergrad, but basically, you push and get so as you're doing your leg extension, you push against it as far as hard as you can, but the speed is kept constant.

So no matter how hard you push, it moves at the same speed. And so that was how they met that was how they measured leg leg power was how hard you could push against this thing. So that that then means you could probably do something similar.

Yes, I think maximum power output on a car or bike or you know, a bike in the gym is a great way to do it. Yeah, or what bike yet? Peloton bike, you know, they would they'll all give you that.

It could also be like, what can you push on a leg press in the gym? Or what can you do with a leg extension, something like that? Like all of those would give you a rough a rough idea.

And so I think in the book, I say if you if you do like a regular leg press in the gym, and you can press double your body weight, right? That's a really, that's a really good indicator for most people. Okay, great.

[Angela Foster] (4:55 - 5:00)
Yeah, okay. So we want to look to double our body weight on the leg extension machine.

[Tommy Wood] (5:01 - 5:04)
Or leg press leg extension, double body weight would be Oh, I did on a leg extension.

[Angela Foster] (5:04 - 5:05)
Okay, well, you go up like that. Yeah.

[Tommy Wood] (5:06 - 5:06)
Yeah.

[Angela Foster] (5:07 - 5:08)
Okay. Oh, on a leg extension.

[Tommy Wood] (5:09 - 5:10)
On a leg. Yes.

[Angela Foster] (5:10 - 5:17)
One thing about a leg press now you're thinking about? Okay, okay. Yeah, I can.

Yeah, I get to multiples on that.

[Tommy Wood] (5:17 - 5:17)
Yeah.

[Angela Foster] (5:17 - 5:23)
Oh, so. So these things are this is important.

[Tommy Wood] (5:24 - 7:04)
Often when people think about, I'm gonna go to the gym, as can be really hard. I have to do a lot of hard work. And and yes, right, you should go to the gym and do hard work.

That is very important for a number of reasons. But the amount of strength you have to achieve is probably less than you think. Almost all the studies that look at strength and dementia risk, disease risk, mortality risk, essentially say that once you're in like the top third to 25% of the average population, right?

That's it. More isn't necessarily better. Now.

Some people want to have more like, my eyes, I enjoy lifting weights, my strength is is is higher up than that. But I also know that I have more than enough to protect me from dementia and death. I do it because I enjoy it.

I'm like, it's my hobby. So just think the way I think about this is that, and this is not for legs, but because we know your grip strength and upper arm strength is really important as well. Think about a room full of people like you.

Similar age, similar sex, right? Sort of similar demographics. If you could be most of them in an arm wrestle, that's more than enough, you're in good shape.

Right? You don't need to like destroy all of them or be the best. You just need to be in that top sort of like 25% compared to like an average population.

And that's less that requires less work than you think. One or two sessions in the gym per week, 30 to 45 minutes, you know, five or six different exercises that cover your whole body, three sets of eight to 12 reps. That's what's been used in these studies that show significant benefits for the brain.

And I think, you know, that's something that achievable, you know, even in a busy schedule for most of us.

[Angela Foster] (7:04 - 8:23)
I hope today's episode inspired you on your journey to vibrant health and high performance. Make sure you check out the show notes for a summary of all the important links to everything we talked about. And if you enjoyed this episode, hit the follow button and share it with a friend on social media or leave a review over on Apple podcasts.

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Angela and special guest Dr Tommy Wood explore the surprising, evidence-backed link between leg power and brain longevity. They discuss how relative leg strength acts as a primary predictor of cognitive processing speed in older adults, driven by the release of exerkines like IGF-1 which protect the brain’s white matter. 

They also reveal that you don't need to be an elite athlete to reap these benefits; simply reaching the top 25% of your demographic can significantly slash your risk of dementia and cognitive decline.

WHAT YOU WILL LEARN

• Relative leg power (strength in proportion to body size) is a critical predictor of how quickly the brain processes information as we age. 
• Strength training triggers the release of hormones like IGF-1, which are essential for maintaining the structure and insulation of the brain's white matter.
• You don't need infinite strength to protect your brain; reaching the top 25% to 33% of your demographic provides the most significant protection against mortality and dementia. 
• Achieving these health benefits is possible with a modest commitment, such as two 45-minute sessions per week focusing on full-body resistance training.