The Best Fitness Program- What does it look like

One of my earliest memories of cardio training was a cold, wet and windy Saturday morning with my U6 Tullamore Hurling team. Hurling, for those who don’t know, is one of Ireland’s national sports and is the best that ever existed. It requires handling skills comparable to hockey with fitness levels far beyond that of soccer, which was the exact aim of that particular day’s session. 20 hooligans running around the pitch with our coaches spurring us on. The aim was to improve our fitness, hoping that it would lead to better athletes and improved performance in the upcoming season. Of course, being only five years of age, it was nothing short of organized chaos.

Though the benefits of cardio are known to be large and vast for everyone from 5-year-old athletes to seniors, there’s an ongoing debate over what the best method to choose is. Is it the time-honored traditional long duration runs and jogs? Or is it methods like HIIT, which became more popular as CrossFit took its hold on the world.

It all leads to a question that us coaches find ourselves asking hundreds of times a day: What is the best method to choose to maximize the return on a person’s time, effort and energy? What should people be doing to get the most progress without injury?

Well, before we get to figuring out what the best form of fitness training is, we need to know how our bodies movement is fueled and what impact different training methods have on it! While we could spend hours talking about it, here’s a quick summary of the must knows.

ATP – Muscle Fuel

Moving our bodies in any way, require the contraction and relaxation of muscles around the body. As we learned in my post on coordination, the nervous system stats this off by sending off the signals to contract. For muscles to be able to follow this command and contract do anything they need a compound called ATP or Adenosine triphosphate.

Three things that you need to know about it:

  • It is stored directly in muscles,
  • It contains three phosphate ions (Hence being triphosphate), and
  • Once used by a muscle, it loses a phosphate ion, becoming ADP or Adenosine diphosphate

So if we need to continue contracting of our muscles we either need to turn ADP back into ATP, or make some brand new ATP molecules! Simple.

Energy Systems

We have three main energy system processes which replenish our bodies with ATP. These are:

  • The Phosphagen system
  • The Glycolic system
  • The Oxidative system

Let’s take a look at each!

Phosphagen system:

Alongside the ATP stored in our muscles is another molecule called creatine phosphate. Now, you may have heard of creatine before, or even taken it – it’s one of the most popular and studied sports performance supplements in the world – but do you know what it does?

When you produce or take creatine it pairs with a single phosphate ion to become creatine phosphate and is stored directly within our muscles. Its job is to donate this phosphate ion to ADP to turn it back into ATP, allowing further contractions to take place. Because creatine phosphate is stored in our muscles (among other places) alongside the ATP/ADP, this process is extremely quick and fast. The one downside being that we don’t have high levels of creatine phosphate within our muscles.

This makes the phosphate system great for high intensity, short duration bouts of exercise, but not so great for longer training sessions.

Glycolytic system:

Anytime we eat or drink carbohydrates – anything from a piece of fruit to a mountain of candy – our bodies break it down into simple sugars which enter our blood stream and become known as glucose. Our bodies will store this glucose within the muscles and tissues around the body where it becomes known as glycogen.

The role of the glycolytic system is to break down this glycogen, through chemical reactions, to produce ATP. This process is a little slower than the Phosphagen system, but is able to produce more ATP.

Oxidative system:

The oxidative system is driven by a process called the Krebs Cycle, a series of ongoing chemical reactions that take multiple fuel sources and turn them into incredibly high levels of ATP. These fuel sources include byproducts of the glycolic system, stored fat, protein and carbohydrates.

The main fuel source that is driving the Krebs Cycle at any one time will depend on the person and activity level in question, but for long duration exercise (Think 3K runs and up) it is mainly driven through fat stores – but that doesn’t mean it is good for losing weight, as I discuss here.

This system is quite slow, requiring compounds, molecules and acids to be transported around the body and long complex chemical reactions to take place, but as already mentioned it can produce incredibly high volumes of ATP.

Because of its slow speed, the oxidative system is great for low intensity, long duration forms of exercise. It is this system that allows people to do incredible things like triathlons and ultramarathons.

An Energy System Summary:

Although these systems are constantly happening alongside one another, one system will be the predominate supplier of ATP at any one time. This is driven by a number of things, not limited to the speed and volume at which each system can supply ATP. This table sums everything up nicely.



So how do these systems connect to the types of cardio that we do?

Out of the three systems, the phosphagen system is anaerobic (requiring no oxygen), the oxidative system is aerobic (needs oxygen) with the glycolic system being both (this system can be broken up into two sub categories; fast and slow. Fast glycolysis in the above table is the anaerobic one, slow glycolysis being the aerobic counterpart). Using the chart above you can see that the first 2 minutes of cardio will mainly be anaerobic and that after 3 minutes your body switches to relying on an aerobic system. While both anaerobic and aerobic training are beneficial, they both have different benefits and drawbacks.

Studies have shown that longer duration, aerobic forms of exercise which use the oxidative system are great for improving aerobic exercise performance and also increasing recovery capabilities. Our bodies need to recover and repair damage from training and our day to day lives. The recovery and repair are driven by processes which are aerobic in nature and because of this, aerobic training is great for helping the entire body recover.

The negative of aerobic training is that is has been shown to promote muscle loss, drive fat storage and reduce overall strength and power levels – not good! (1), (2), (3), (4).

On the other hand, anaerobic exercise like sprints and HIIT, which mainly use the phosphagen system and fast glycolysis have been shown to increase the levels of ATP, glycogen and creatine phosphate stored within muscles and also improve aerobic activity performance levels (5), (6), (7). This is awesome: Anaerobic training will not only improve short term performance, but long term performance too. If you are training for muscle gain, fat loss or improved fitness, your efforts should be focused on the bike sprints over the long distance work!

The downside of anaerobic training is that it is incredibly challenging; not only does it require you to push yourself right to the limit of your speed and power, but it can also make you feel sick, light headed and woozy. That said, these are all things that you can become accustomed to through practice and smart progression processes.

Studies and research aside, I have seen the best results with my clients and athletes through anaerobic training processes, allowing them to add in aerobic training for their own enjoyment if they like it. The improved performance across the board that it drives, along with minimizing the negatives of fat storage and muscle loss that come with aerobic training yielded the best results for them.

A basic anaerobic training program is comprised of simple bike sprints. 4-10 rounds of 10 seconds incredibly high intensity, all out speed, with 50 seconds of rest is a good place to start. This could be built up to 30 seconds on, 120 seconds off, which will provide a challenge that only the fittest of fit could complete.


Fueling our activity and exercise is something that is highly complex in nature, but something we can affect with very simple and effective workouts. Although there are benefits to longer duration cardio, there are vastly more significant benefits of short duration high intensity exercise. Anaerobic conditioning can make you fitter, help you keep your muscle levels high, your fat stores low, and still improve your long duration activity abilities!

  • Oxidative and lysomal capacity in skeletal muscle. Vhko, V. 1978.
  • The effects of running, weightlifting and a combination of both on growth hormone release. Craig, B.W. 1991.
  • The available glycogen in man and the connection between rate of oxygen intake and carbohydrate usage. Hadmann, R. 1957.
  • Interference of strength development by simultaneously training for strength and endurance. Hickson, RC. 1980.
  • Potential for strength and endurance training to amplify endurance performance. Hickson, RC. 1988.
  • Strength training effects on aerobic power and short term endurance. Hickson, RC. 1980.
  • Health and performance related adaptations to resistive training. Stone, MH. 1970.


Shane Carberry

Shane Carberry is a senior strength and conditioning coach at the Athlete Factory, specializing in speed and acceleration training. Originally hailing from Ireland, Shane also worked as mechanical engineering before transitioning to a strength and conditioning coach. Read his articles, check out his website and give him a follow on Twitter @somethingawsome.

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