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Tri 101: Training Intensity Explained

The New Year has passed. The upcoming race season starts soon. And to get ready here’s my thoughts on finding the right training intensity to be your best. Here we go!

It’s not how much you workout that will make or break your race performances but rather the intensity with which you do your training. And to understand how to optimize your human genetics to gain the fitness you’ll need for an endurance event, let’s look back in time at how our genetics were honed based on survival. Understanding that will help you craft training intensity to match what we are hardwired to do!

You’ve got two main sources of fuel stored in your body that you use when you move. They are fats and carbs. It’s that simple!

There’s enough fat stored in our bodies to go about 500 miles. But there’s only enough carbs stored as glycogen to go about 20 miles. That’s why the bonk always happens in a marathon around that 20 mile mark. A runner burns through their stored carbs and then are of gas. Why is that? Because carb burning blocks fat burning. And once that happens  fat burning doesn’t come back fully online for 7-9 hours. So even if you slow down, fat burning is barely sputtering along.

But back to fats and carbs. At a low to moderate training intensity you can utilize stored fat quite efficiently if you have stimulated your body to be able to use it by doing the right kind of training intensity (I’ll get to that specifically in a minute). This is called aerobic metabolism. It means you can get oxygen in quick enough to break down more fat than carbs to fuel your exercise.

But once you hit a certain point called your maximum aerobic pace, if you increase your training intensity you shift over into burning more carbs than fat. This happens because carbs break down with less oxygen than fat to release their energy for exercise. This is anaerobic metabolism.

Remember, we can go long distances from stored fats but not very far on stored carbs.

We evolved to be the best endurance animals on the planet. Our ancient ancestors spent the vast majority of their time doing moderate movement over long periods of time. They were burning that diesel fuel called stored fat.

Then of course on occasion they had to sprint to escape danger, at which point we evolved to shut off slow burning fat as the source of fuel and shift into high octane carb metabolism. It’s all about survival. You don’t want to be on slow burn mode when a sabertooth tiger comes running toward you looking at you like you are its next lunch! You want to get the heck out of the way!

Fast forward to modern times and how many athletes train. It’s HIITS workouts and fast stuff done in groups on a regular basis. The training intensity is basically a daily diet where they get an anaerobic component into every session. Anaerobic training is physiologically high stress on the body.

Your ancient genetics interprets that sprint to the finish with your training buddies as a signal that there is danger around. And even if the rest of the workout was aerobic, here’s what happens. As you recover your body will strive to up the fitness of the anaerobic metabolism rather than build your fat burning aerobic physiology.

Why would our bodies choose developing carb burning over fat burning if both were used in a workout?

Well, a look back in time gives a good theory on that. As I mentioned our ancient ancestors mostly moved at low to moderate intensity levels. They spent a LOT of time in the fat burning zones. They spent very little time at the anaerobic mostly carb burning intensities. If you were running away from a saber tooth tiger on a daily basis, chances are you would get caught and not live very long!

So, with very few chances to actually stimulate that flight or fight high stress anaerobic metabolism, when it did happen it was important to hone in and develop it when it was used. There would be plenty of other days to work on the fat burning fitness of daily life.

But again, high intensity training is high stress. Your adrenal system get activated. It’s the system in your body that turns on carb burning and shuts off fat burning so that you can get away from danger.  The adrenal system is like a reserve battery. It’s your internal energetic reserve. A little bit of pulling from that is fine. But doing it most of the time drains that essential reserve and it cannot recharge as quickly as it gets used. This is the classic hard training athlete. The result is a quick plateau in performance and usually someone who is burned out or injured or sick. None of those things are going to help make you a better athlete.

There is no shortcut. As you build your fitness, the vast majority of your workouts should be at a training intensity that is aerobic.

Yes, you can go hard a lot of the time and your fitness will build quickly. But it will be a short lived upward curve.  Then there can be a slide in fitness even though you train all the time.

Building your aerobic fitness does take patience. You may have to slow down a lot initially if you have never trained your aerobic base. Yes, there will come a time when it is important to add in a higher training intensity when you get close to your races. But initially, take the time to build that base.

Here is a video with a deep dive into the whole concept of aerobic and anaerobic training:


Here is a lighter look at training intensity as only Tommy Buzzcut can put it:


Join us at Mark Allen Coaching and train smarter not harder!

(This is the first in a 9-part series of blogs on tips to help you train and race at your best!)



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