Cardio Explained (Zone 2, HIIT, Skinny guys, Fat guys ALL explained)

If you understand cardio by the end of this post, you’ll have the tools to add years to your life

And increase quality of life.

-To start, here is a chart showing cardio zones, I will explain it in details

Doing cardio is not a random process. There is proven, factual science to training your cardiovascular health.

The way you improve cardio is similar to training muscles

You achieve certain levels of intensity in your training, intensity in this case being your HEART RATE

Why does heart rate matter?

You need to know it because it tells you how hard you working

The way you assess and progress cardio is by measuring your heart, and comparing it to your Maximum Heart Rate (or Heart Rate Max, as shown in the chart)

There is a formula for this.

The formula for determining maximum HR is 220, minus your age.

so if you are say 20 years old

220-20 is 200

200 is your max heart rate during exercise

-This formula not perfect, but heuristically it applies to the overall majority of population

Lets learn how to use it… 

So we have Zones

  • Zone 1 – 50-59% of Max heart rate
  • Zone 2 – 60-69%
  • Zone 3 – 70-79%
  • Zone 4 – 80-89%
  • Zone 5 – 90% to 100%

We are going to do MATH (oh god no)

Using the example of a 20 something young person

200 x 0.60=120

200 x 0.69=138 

So for someone that is 20 years old, Zone 2 would be cardio that keeps your HR between 120-138

For someone that is 40 years old, it would be cardio that is 108-124 BPM

Simple enough.

Why do Zone 2 though? 

Benefits of Zone 2 Heart Rate Training:

  • Increase in the number of mitochondria
  • increase in mitochondrial efficiency
  • increase in “metabolic flexibility”
  • lower resting heart rate
  • a decrease in blood pressure
  • lower risk of injury
  • improves insulin resistance 

Zone 2 has tons of upside, and no real downsides. Its easy to recover from, and its health benefits are immense.

Zone 2 Heart Rate Training For Longevity and Performance

Whether you are optimizing your exercise regimen for performance, or to live longer, Zone 2 heart rate training deserves your attention. This article will concentrate on the importance of Zone 2…

Where Cardio can get CONFUSING

A lot of recommendations you find online are not based on the Zones, but on the classification of “Moderate” and “Vigorous” intensity (these come from American College of Sports Medicine)… 

Moderate intensity is 64-76% of MHR

Vigorous Intensity 77-93% of MHR

This is basically Zone 2 to Zone 3

And then Zone 3 to Zone 5 


The old recommendation by various institutions and the government health council was 150 minutes moderate intensity, and 75 minutes Vigorous

these were updated recently.

The new recommendations are DOUBLE the old ones 

150 minutes moderate intensity, and/or 75 minutes vigorous at minimum

For optimal health, 300 minutes moderate intensity, and/or up to 150 minutes vigorous intensity 

That works out to 20-60 minutes of walking daily for moderate intensity

For vigorous intensity, thats anywhere from 2-4, 20-40 minute intense workouts each week

Why the increased recommendations?

Physically active people simply live longer and have all around better health. 

To circle back to Zone 2 cardio: Aside from the health benefits, its the “easiest” cardio to do

Intense enough, but not too intense

It can be walking, jogging, spin bike, anything that elevates your heart rate and you can do for reasonably long periods of time.


Im sure someone will ask about this,

High intensity interval training promotes similar adaptations to Zone 2 and 3 cardio

its basically training at the “vigorous” intensity level

Is it better though?

It comes down to context… 

It takes less time, but HIIT workouts can be harder to program and manage

In the fitness world, they are notorious for being a shitshow of exercises thrown together with no real progression model at all other than trying to work people to death as fast a possible

If you are going to do HIIT, it needs to be something, safe, and doable, and consistent


The formula gets screwed entirely by very fit older people, it does NOT apply to you

Someone could be 70, but if they are cardiovascularly in peak shape, their biological age could be 35.

So if you are an older person reading this and concerned that your HR is way higher than recommended by the formula,

You are probably fine.

My father is 65 and can still get his HR to 200 when he pushes it. He has been a runner his whole life. Formula doesnt count for him 


Reality check-walking for 20-30 minutes is not going to destroy your gains

This idea of doing ZERO cardio if you trying to gain weight is largely ridiculous

A walk is not making you lose muscle, period. 

What about for FAT LOSS???

Fat loss comes from a CALORIE DEFICIT

while this can be achieved through exercise, this is not sustainable. The weight comes back if your exercise volume decreases, and trying to train more and eat less leads to burnout and metabolic slowdown 

If you want fat loss, change your DIET

High protein, higher satiation, more thermogenic foods, and a sustained calorie deficit for guaranted fat loss.

(I do have a program for this, fyi)

AJAC Accelerated Fat Loss 4.0

If there are any more questions feel free to ask me in Twitter at @aja_cortes.

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