What Interval Training Actually Improves

Before getting into the sessions themselves, it helps to understand what you’re actually training.

You’ll often hear terms like VO₂ max and lactate threshold. They sound technical, but the ideas behind them are simple — and they make a real difference to how you run.

VO₂ max is your body’s ability to use oxygen when you’re working hard. The higher it is, the more efficiently you can keep going at faster speeds. Interval sessions that push you close to your limits help improve this, which is why they often feel tough but controlled.

Lactate threshold is the point where running starts to feel noticeably harder and less sustainable. It’s the difference between a pace you can hold for a long time and one that quickly catches up with you. Training just below or around this level helps you push that line further out — so what used to feel hard becomes manageable.

There’s also a more practical side to it.

Intervals help you learn how to change gears. To run hard, recover, and go again. That ability to control effort — especially when terrain, fatigue, or conditions change — is what really matters out on the trails.

You don’t need to overthink the science.

But understanding what’s going on in the background makes it much easier to see why these sessions work — and how to use them to your advantage.