Peter Attia

And therefore, as output increases and demand increases, lactate production in the type 2 fibers begins to exceed the capacity for what can be done locally in the mitochondria adjacent.

And at that point, lactate spills into the bloodstream.

So if you were measuring lactate in the bloodstream with a continuous lactate monitor, which by the way, these things are easily in prototype and there's some that are probably on the market.

So this would be something you can appreciate in the future.

You might start out an exercise session where your lactate is resting at 0.5 millimole

Everything I just described up until this point would not increase that, even though locally lactate levels are rising.

But once it starts spilling into the bloodstream, now you actually have to rely on other tissues in the body, the heart, other muscles that are not being utilized at this point in time.

They have to start clearing it using lactate as fuel, as we've even learned from George Brooks.

The brain will do this as well.

The liver also can convert that lactate back into glucose via gluconeogenesis.

And this basically allows the body to maintain certain levels of lactate at a new baseline that is above the original baseline.

This is usually referred to as the first lactate threshold.

And again, for a metabolically healthy individual and someone who's metabolically flexible, meaning they can go back and forth between utilizing glucose and fatty acids, this falls at about 2%.

2 millimole of lactate.

That is what we refer to as zone 2.

Again, if some of those conditions aren't met, if you're not a metabolically flexible person, using that first threshold of lactate at 2 millimole is not going to happen.

There are people who walk around at rest with a lactate level above 2.

Okay.

But the point here is you can maintain, you're now at a new steady state where, if you remember, the first steady state is where the local tissues are able to offset lactate production at the rate that it's being produced, consumption and production are equal locally.

then you have this second level which we refer to as the first lactate threshold because it's the first one we're measuring in the plasma and that's where now the systemic tissues are able to balance it.