The gym can be a confusing, and sometimes intimidating place for some. It doesn’t help that our industry has saturated the market with fad diets, hype men preaching “bro science”, and just generally poor advice. How do we sort fact from fiction to ensure we are making the right choices? It’s the same in the gym as it is in any other space…educate yourself! Our Coaches Corner blog is all about educating our followers. This time we will cover cardio, and the how and why your body responds to different forms of cardio to net you the results you want!

We’ve all heard “that guy” before. The one who says you can’t lose fat unless you try fasted cardio, or maybe the one who says high intensity interval training (HIIT) is the only way to burn fat and keep your muscle, and my personal favorite….”cardio kills gains bro, I wouldn’t want to lose my muscle.” What should you do? After you’ve selected a type of cardio, whats next? Is there a certain time of day I should be training? Is one piece of equipment better than the others? In short, you want to get the most out of your cardio sessions. In order to get the best results you need to understand how your body responds to exercise at the cellular level. It’s not that different types of cardio are better or worse than another, it’s that they are completely different and even use different fuel sources in different amounts!

The human body has 3 metabolic pathways, or energy systems, that need macro nutrients to fuel our bodies. Carbohydrates (CHO), Fats and lipids (FAT), and proteins (PRO) can all be utilized in varying amounts based on your cardio training style, intensity, duration, and nutrition habits leading up to the activity.

Actvities pictured are all examples of exercises that would be primarily accomplished through the phospho-creatine system

Phospho-creatine system (ATP-PCR) - This energy system is active for the first 15 seconds of any exercise. The phospho-creatine system uses creatine and phosphates broken off of sugars in the body to give us EXPLOSIVE energy. Just like anything that explodes, it’s a pretty quick burn and it takes 2-5 minutes to replenish. A good example of the ATP-PCR system in action would be a 1 rep max or a vertical jump test. Can you train your cardio system using the phospho-creatine system? Yes! Sprinters use this system primarily as they have an extremely high energy demand for a very short event. The ATP-PCR system may not be in 1st place for fat loss, but it definitely shouldn’t be ignored if performance is part of your goal.

High intensity exercises that are shorter in duration than 2min are anaerobic in nature. Push ups, many skills movements, HIIT training all fall into this category.

Anaerobic Glycolysis - any exercise that lasts between 15 seconds to 2 minutes would be considered anaerobic in nature. Anaerobic activity pulls exclusively from stored glycogen in our muscles for fuel. Good examples of anaerobic activity would be HIIT training, a tabata routine, or even a set of 20 push ups. The higher intensity may burn more CHO by percentage than FAT to fuel anaerobic activity, but the catch is that you will burn calories for HOURS after you’ve completed your workout! Anaerobic exercise places alot of stress on your body, and recovery takes both time and energy to get back up to 100%. When incorporating anaerobic activities it’s important to remember the toll these take on the body. It’s not harmful, but taking all things in moderation it’s definitely possible to over do it.

Long, low intensity activities are aerobic in nature and tend to burn more fat by overall percentage.

Aerobic Glycolysis - exercise that lasts for longer than 2 minutes is aerobic in nature, and will utilize CHO and FATS with Oxygen to provide a longer burning fuel for a longer event. The amount of CHO and FAT burned depends entirely on the person and their cardiovasular fitness level. An example of aerobic activity would be going for a 5 mile run, or even walking around the neighborhood. Aerobic activity is probably the most common form of exercise we find ourselves doing. This might be because of the low impact profile of aerobic activity. This is a great starting point for many who are trying to leave their sedentary nature behind them, lose fat, or even incorporate for an active recovery day.

So. We all have energy systems. Cool…… but, now what? Now that we know how our bodies will fuel our efforts, how do we program a cardio workout for our goal?

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Diagram: Lower intensity cardio uses more FAT, while higher intensity uses more CHO.

Giving our diagram a look, you can see that FAT is burned more by percentage at a lower intensity than high intensity. This doesn’t mean HIIT isn’t good for you…I’ll elaborate here shortly. Utlimately, higher intensity exercises will burn more CHO by percentage. Let’s break this down a bit further with an example. Let’s say you are stuck between choosing the stairmaster for a 45 minute steady state cardio session, or the treadmill for a 25min HIIT routine. Which one should you choose for optimal fat burning? The answer isn’t as definitive as you’d probably hoped so we will give you BOTH correct answers. The reality is they are both equally effective under the right circumstances.

Steady state cardio tends to burn more fat by percentage as the intensity is lower than HIIT. For optimal results, this can be paired with a fasted cardio session to maximize fat loss! In a fasted state, the body lacks a full store of glycogen in the muscles, meaning you can burn through the reserve glycogen levels with relative ease and burn FAT for the majority of your cardio session. Simply put, the longer you move for, the more fat you’re going to burn.

A HIIT session can only be optimized by ensuring you have the proper fuel. A fasted state would actually lessen the potential fat loss impact a HIIT session can have. In short, imagine you are trying to race a car on a 1/4 of a tank. You may start off as fast as the rest of the pack, but you will inevitably run out of fuel. The catch 22 is that once you’re out of CHO as fuel, the body can’t use FAT as a fuel source for an anaerobic activity. What you fuel up with prior to a HIIT session is largely dependent on when you intend to workout. An apple tends to be my go to as it provides us both quick acting simple sugars, and longer releasing fructose that will continue to provide energy throughout the workout! The best part about HIIT though….you burn calories even AFTER you’ve finished! Sometimes up to 2 or 3 hours after you’ve hit the showers. Talk about efficiency!

Cardio is necessary no matter what your goal, your sport, age, health history, whatever. Your heart and lungs need to be efficient to maintain adequate levels of overall health. If you want to maximize the results you get from your hard work, the information provided in this article is sure to take your training to the next level.

Mix up your training some, and incorporate a little bit of everything to make sure you aren’t leaving out any of your energy systems, and you’ll be well on your way to whatever your goal is.

In health,

Jake Hixon

Cardio Talk: Aerobic vs. Anaerobic Exercise