Beginner Series

What is optimal cardio fitness?

Optimal Humans

What is the optimal level of cardio fitness

High level of cardio fitness is non-negotiable for physical performance 

Whether you’re competing for glory, throwing frisbee with the kids, or just running to get to the bus stop in time. Cardio fitness is the engine that allows you to maintain strenuous physical activity for longer and recover faster.

It is also the best indicator of your overall health

As the key to longevity, cardio fitness has been proven to reduce the risk of stroke and heart attack, among other health conditions. This makes cardio fitness perhaps the most important piece in your health puzzle.

Cardio fitness is defined as either aerobic or anaerobic

With some overlap between the two. And since we’re on the quest to optimise health and performance, it’s crucial to understand the difference between aerobic and anaerobic systems

Your body uses the aerobic energy system to go long 

This is typically any effort that's done at a low to medium pace for a prolonged time. Long bike rides, jogging, and hiking all fit in here.

Aerobic effort uses the body's cardiovascular system to absorb and transport oxygen for the working muscles. It’ll help turn glucose and fats for energy. While also transporting the by-products of this process away from the muscles.

Now, let’s say you’re on a bike ride and need to climb a steep hill for 30 seconds. That’s when your anaerobic energy system kicks in gear.

You need the anaerobic energy system in any activity that is short, but high in intensity

This includes activities such as weight training, or sprinting up that hill on your bike. When the body requires a significant amount of energy quickly, it can’t get the oxygen fast enough. It has to change how it makes energy. 

Unlike aerobic exercise, anaerobic (literally, "without air") doesn't require oxygen to produce energy. Yes, your body still relies primarily on glucose. But it can only sustain this anaerobic output for relatively short bursts before the lactic acid accumulates in the muscles.

This build up of lactic acid leads to the burning sensation in the muscles during a high-intensity effort. This, once unbearable, is the anaerobic threshold. Also known as the handbrake on output.

You can improve your anaerobic threshold with specific high intensity training in and around your threshold. Ideally once you have a solid aerobic base.

Testing your cardio fitness levels

We recommend using Concept 2 ergs or running for all the fitness tests (except dry breath hold) in the Optimal Humans app. You can find Concept 2 ergs in most gyms, which makes comparing test results more accurate, regardless of your location. When running, choose a flat course, outside. Preferably a running track. Treadmills are great in a clinical setting for VO2 max testing. Though not accurate when considering distance and speed over time.

Concept 2 also has a vast database of records from around the world, which makes it easier to see how you stack up against others in your age, weight and gender group.

That being said, you can choose the testing equipment that works the best for your situation. In the app you have the option to run, bike, swim, row or use the ski-erg. Choose the piece of equipment that best fits your goals and. If you’re a runner who wants to get better at running and you’re not familiar with rowing, run.

The optimal level of aerobic fitness

In the Optimal Humans app, we use two aerobic fitness tests.

20 minute maximum aerobic function (MAF) Test: 4km - 4.9km. You have to stay at your maximum aerobic heart rate (180 - your age +/- 5-10 points depending on your health and fitness level) and breathe only through the nose. 

Dry breath hold test: 90 seconds - 119 seconds. To assess the quality of your breathing pattern and your carbon dioxide tolerance. 

There is some emerging science that the time of your breath hold, and therefore your carbon dioxide tolerance, may be a better indicator of your overall health than blood pressure.

The optimal level of anaerobic fitness

We use three separate tests to set the benchmarks for anaerobic fitness. Again, using the Concept 2 rower.

30 minute challenge: 6km - 7.9km. 

What makes this different from MAF above, is in the word “challenge”. You literally give everything you’ve got for a 30 minute effort to see how you stack up. Not only physically, but also mentally.

2000 meter long sprint: 8 minutes - 7 minutes. 

One of the most used tests with Concept 2 rowers with years of data.

500m meter pure anaerobic effort: 2 minutes - 1:41 minutes. 

It’s the only short max effort test in the Optimal Humans app.


Cardio fitness is the engine that allows you to maintain strenuous physical activity for longer and recover faster. It is also the best indicator of your overall health.

Aerobic and anaerobic energy systems work together and compliment each other. The key to understanding them is that the aerobic system is for prolonged, low- to medium-intensity exercise, while the anaerobic system is for brief, high-intensity exercise.

We recommend using Concept 2 rowers for all of the fitness tests (except dry breath hold) in the Optimal Humans app. You can find Concept 2 rowers in most gyms. This makes comparing test results more accurate, regardless of your location. There’s also years of data on Concept 2 website so it’s easy to compare your results with your peers. 

That being said, if you’re a runner with the goal of getting better at running, we recommend you use running to benchmark your cardio fitness.

For Training: Establishing Zones & Thresholds

More advanced concepts.

Using this calculator will give you insight into your estimated heart rate for each training zone. Which will allow you to estimate your aerobic and anaerobic thresholds.

Enter in your age and resting heart rate and the following table will be generated.

This is an estimate.

Your aerobic zone is estimated to be between 141-155. Your aerobic threshold is around 155 give or take a few beats.

Your anaerobic zone is estimated to be between 155-169. Your anaerobic threshold is around 169 give or take a few beats.

The goal of training is to increase your thresholds over time, meaning more work done with less effort.

This info comes in handy when considering the Polarised training method and choosing the best intensity for training.

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