Why Exercise Intensity Matters Beyond Step Counts

Steven Bartlett: And physiologically what is going on in my body when I get to that 85% to 90% effort range and I stay there for a couple of minutes that doesn't occur when I'm doing my StairMaster.

Dr. Rhonda Patrick: So many things are happening. There are a lot of different physiological responses that are—

Steven Bartlett: You've got a big smile on your face when I ask.

Dr. Rhonda Patrick: Yes, I do because it's one of my favorite things to talk about, and it has to do with when you're pushing yourself really hard, you need to make energy, right? And the way that most of our cells make energy, like our muscles, is by using our mitochondria. These are tiny organelles inside of our cells that produce energy, but they need oxygen to do it. So, that's where the oxygen comes into play. When you start to push yourself really hard, you can't get the oxygen to your muscles quickly enough, but you need to make the energy.

And so, your body decides to make energy in the form of ATP without the mitochondria. It uses glucose to do that. You're not making as many of those ATP energy molecules, but you're still making them, and you're making them quickly. And that's what your body wants to do.

And so it's using glucose to do that without the mitochondria, but as a byproduct, it's making something called lactate. And this is what gets me so excited because, for the longest time, lactate was thought to be just this metabolic byproduct of glucose metabolism. When you're pushing yourself really hard, it's called anaerobic, by the way. You're not only anaerobic; you're just somewhat anaerobic.

You're still producing energy with your mitochondria. You're also producing it without the mitochondria. It's not a black-and-white thing, right? It's a little bit gray.

But the reality is you're producing something called lactate. And for the longest time it was thought, oh, this lactate is just bad because it can form lactic acid, and that causes the burn in your muscles. This was decades ago. And we now know from the work of George Brooks at UC Berkeley that lactate itself isn't causing the burn.

And not only is it not causing the burn, it's like a miracle molecule that's being made. This metabolite, lactate, gets into your circulation and it gets consumed by your heart, by your brain, by your liver, and it's used for energy. It's very much similar to beta-hydroxybutyrate, that ketone body that you always hear people talk about when they're fasting or doing a ketogenic diet. It's actually very similar to that.

It gets transported through the same transporter, and it's used for energy, very similar to that. But what's more exciting is that lactate is a way for your muscles to communicate with other organs, like the brain. It's called a signaling molecule. So your muscles are going, "I'm working really hard."

"This is really hard. We have to respond to this work. We have to adapt." And so your body goes, "Okay, I've got to turn on all this awesome stuff that I have because I'm working so hard."

"I need to respond to that so that I'm good," right? And so what happens is, this has been shown, the lactate gets consumed a lot by the brain. And in the brain, it activates something called brain-derived neurotrophic factor, BDNF. And this is kind of like Miracle-Gro for your brain.

So essentially, it's able to increase the growth of new neurons, which is amazing. It's called neurogenesis. It increases the connections between neurons. So it improves memory, cognition, and then it's involved in what's called neuroplasticity.

So, the ability of your brain to adapt to a changing environment. This is all from lactate. It also increases neurotransmitters like norepinephrine, so focus and attention; serotonin, your mood, you're feeling better, you're motivated. All these things are happening because of lactate. There have been studies in humans comparing people working out hard with vigorous exercise versus moderate- to light-intensity exercise. They make more lactate, and it's been shown that high levels of lactate are correlated with improved cognition scores and improved impulse control. So serotonin plays a role in impulse control.

So you're able to not just act on your impulse, right? You're able to, which is great if you want more focus and attention, right? So this is all really exciting stuff because it comes down to your muscles being these little chemical pharmaceutical factories. And the way to make them produce these pharmaceuticals is to work them, to challenge them. That can be done with an easy high-intensity interval training protocol. A variety of them, like a Norwegian 4x4, can increase brain-derived neurotrophic factor. That's been shown.

The one-minute-on, one-minute-off protocol also has been shown to increase that through lactate. So that's one of the big differences between vigorous-intensity exercise and more moderate- or low-intensity exercise. And I honestly think the guidelines, everyone's sort of obsessed with steps: "I need to get my 10,000 steps in, my 10,000 steps."

And they have wearable devices. And I think that's great, but I think we need to change the 10,000 steps to at least 10 minutes of vigorous-intensity exercise. You could do 10 minutes of any type of exercise that's really going to get your heart rate up, and it's going to be so much better.

Steven Bartlett: So, this is a really dumb question, but it's the question that I had in my mind, which is: if lactate is such a miracle drug, why can't I just drink it?

Why can't I just get a shot of lactate versus having to go through vigorous interval training?

Dr. Rhonda Patrick: It's a great question, Steven, because there have been studies looking at, for example, traumatic brain injury patients. So, people who have undergone some sort of head trauma, and they've infused sodium lactate through an IV into their system. The lactate immediately gets consumed by the brain, and it's been shown to improve their recovery. So, it's called the Glasgow score.

You may have heard of it, but it's essentially this battery of tests that's done to assess how someone's recovering from traumatic brain injury. And the sodium lactate does improve that. So, you can find different types of lactate that you can consume. And theoretically, it should help, but what happens is, when you consume the lactate, it actually gets used by the gut.

So a lot of it is going into the gut cells before it gets into your circulation.

Steven Bartlett: There's always a trade-off with these bloody things. Whenever you try to trick the system or shortcut the system by drinking something, I feel like there's a trade-off that people don't talk about a lot.

Dr. Rhonda Patrick: Well, the thing is that it is good for the gut.

In fact, a former colleague of mine, Mark Shigenaga, has shown that lactate is really beneficial for the gut epithelial cells. In fact, if you think about it, all these sort of beneficial probiotic bacteria, like Bifidobacterium, for example, they're producing lactic acid, and that lactic acid does get converted into lactate. It's sort of like this physiological homeostasis where you have the difference of just a hydrogen atom. So, you're having lactic acid and lactate sort of in this equilibrium, so to speak.

But those bacteria in your gut are making lactate, essentially. And the reason it's so good is because it is a very easily usable source of energy for the gut cells. So, not to go off on a tangent here, yes, there is always a trade-off, especially for doing something orally. But when it comes to exercise, like I mentioned when we first started talking about exercise, if you could pill up what exercise does, it's so many things, right?

It's not just the lactate.

Steven Bartlett: Yeah.

Dr. Rhonda Patrick: So many different things, so many different adaptations that occur. It would be a miracle drug. So, you're not just getting the lactate; you're getting the improvement in cardiorespiratory fitness. You're getting the muscular response, right?

The adaptations to your muscle. You're increasing stress-response genes like heat-shock proteins that are important for preventing neurodegenerative disease. You're making antioxidants because of the inflammation that you're generating while you're exercising. There are hundreds and hundreds of things that are happening all in concert from exercise, and you just can't pill it.