Spencer Matthews

It's such an incredible physical feat.

It really is.

It's just so wild.

It's extraordinary.

Anyone who runs will look at someone who puts out a 209 and just, there's reverence in every word because it's so hardcore on so many levels.

Yeah, so running zones have historically been a way of trying to gauge which energy system I'm using to perform the task.

So human beings are much like a...

an electric car which i could potentially use the prius as our early example that at relatively low combustion rates so when your prius is pulling out of the car park it's probably silent and then as it speeds down the a430 it would move from being a silent vehicle to a petrol powered vehicle because as it requires that higher speed it requires a different fuel mix

and humans are the same.

So as we're running at low intensity, we can use a really efficient fuel, which is fat and oxygen to combust the energy that we are using now.

So as you and I sit here now, you'd like to think, unless we've had some crazy glucose drink or some wild energy drink, we will be performing these energetic tasks of communicating and having a lovely time using fat and oxygen to generate fuel.

If we then started walking and then running faster and running faster, we get to a point where our body can't deliver that energy using that same fuel source.

So it starts to subsidize

the fat with a bit of carbohydrate, and it starts to lose some of the availability of oxygen.

And as our body moves from a really clean fuel without consequence, so we could sit here all day, it moves to feel like a dirtier fuel mix, which comes with consequence, most notably the byproduct of fatigue, which could be a change in the acidity of the muscles, this rise of lactic acid, which is often misappropriated as the cause of fatigue, but certainly correlates with fatigue.

And the faster and harder the body works,

the more I change the fuel mix and my ability to do that for a certain period of time.

And someone basically stratified these into five zones, which theoretically correlate with my body moving from using aerobic and fat metabolism to carbohydrate anaerobic metabolism.

I am working with sugar and no oxygen, having started with fat and oxygen.

And the zones are sort of, you know, 50 to 60% of my maximum heart rate, which in itself is a debate, is zone one.