This is your body on base training

Steady, moderate-paced, base-building rides perform their own unique metabolic magic.
Steady, moderate-paced, base-building rides perform their own unique metabolic magic.

Don’t. Steady, moderate-paced, base-building rides perform their own unique metabolic magic you don’t want to miss out on.

Just ask Inigo San Millan, PhD, of The University of Colorado Sports Medicine and Performance Center (CUSM&PC) in Boulder, Colorado, who has helped thousands of riders, runners and swimmers get faster by slowing down.

“Zone 2 training is harder than a recovery ride, but not so hard that you can’t talk the whole time. Depending on your fitness level, it’s between 55 to 75% of your VO2 max intensity or about a 5 to 6 on a 1 to 10 scale,” says San Millan.

“This is where you’re burning the most fat for energy before you cross the threshold into more carbohydrate burning. The majority of your rides – about 75% of your training time during base training period – should be here for the best training benefits. Stick to it three to four days a week in the first several weeks of training and you’ll see your watts go up as your heart rate and perceived exertion remains the same.”

You burn fat

When you ride at base-building intensity, you’re primarily using your aerobic, Type I, slow twitch fibres to do the work. These fibres fuel themselves mostly with stored fat and just a little bit of carbohydrate.

Burning fat = good thing.

You build more mitochondria

Type I fibres are home to the bulk of your muscle’s energy producing mitochondria. When you devote time to building your base, you’re actually stimulating mitochondria growth and improving their function, so you become an even better fat burner.

That’s a key benefit of building a big base. Your body becomes so good at burning fat that you preserve your precious glycogen stores, which gives you the energy you need to go hard at the end of a long ride or race.

You get really good at using oxygen

Because you’re using lots of oxygen during base training, your body adapts to make it easier for you to get as much oxygen as possible into your working muscles with every heartbeat.

That means your heart gets stronger to pump out more blood per beat and your body lays down a larger network of capillaries within your muscles so you can deliver more oxygen and nutrients and carry out more carbon dioxide and metabolic waste products per minute.

You become more metabolically flexible

The bigger your base, the more metabolic flexibility you have, which is a fancy way of saying that your body gets adept at switching back and forth between fuel sources (carbs and fat) as needed. That has benefits on the bike, such as burning more fat to keep you from bonking when fuel’s running low.

You clear lactate faster

Your Type I, slow twitch fibres do more than burn fat, they also clear lactate. It works like this: when you ride harder than your Type I muscles can handle, like in a sprint, the fast-twitch Type II muscle fibres step in and start blasting glucose from glycogen (stored carbs) for energy.

The byproduct of this process is lactate. By now you know that lactate is not the enemy, but rather a fuel source that can be used to make energy in your muscles and other cells – but the hydrogen ions associated with lactate can accumulate and interfere with muscle contraction, which is when you slow down.

You need to be able to clear lactate out of your fast-twitch muscle fibres ASAP, and that’s your Type I fibres’ job.

They do it through a process called the mitochondrial lactate oxidation complex (mLOC) – which is indeed complex. In short, your fast twitch fibres shuttle lactate using special transporters called MCT-4, where it then hitches a ride into your slow twitch fibres (which contain the most mitochondria) via their own special MCT-1 transporters.

Once inside the slow-twitch fibres, the mLOC works its magic to re-use lactate for energy. Base training increases these transporters and your mitochondria, improving the whole mLOC system so you can clear more lactate faster and go harder for longer.

You become more resilient

None of this is to say that you don’t need high intensity training. You need to train those Type II turbo fibres to build your top end. High-intensity training also delivers aerobic, fat burning benefits of its own. That’s why you should be spending about 15 to 20% of your base training time doing some high intensity rides.

Just keep in mind that hard training is metabolically disruptive; breaking down muscle tissue and increasing inflammation.

If you try to stack that type of training on top of a shallow base, you run the risk of injury, burnout and going backwards instead of making progress.

By maintaining a large base, you’re not only more resilient to withstand those hard, heavy training loads, but also you’re giving your body the kind of easier rides it needs to repair and regenerate. That makes you stronger, faster and gives you more happiness watts to boot.

This article was originally featured on

Image credit: iStock

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