You may hear runners or coaches talk about “aerobic” or “anaerobic” training and wonder what it means and how it might be relevant to your training. Below, we explore these terms and combat some misconceptions to help you better understand the different intensities that can affect your fitness — and how you can apply that understanding to make your workout more effective.
The terms aerobic and anaerobic have long been used to differentiate between different running intensities and play a role in the origin of the different training zones and thresholds.
Essentially, these terms refer to energy. Adenosine triphosphate (ATP) is the “currency” your body uses to produce the energy it needs to run. To sustain extended periods of running – or multiple runs (e.g. during an interval session) – your body needs to replenish this ATP and will do so through both aerobic and anaerobic means.
What is Aerobics?
Aerobic exercise is a term commonly used to refer to activities that primarily use oxygen to generate energy. During aerobic exercise, your body relies on a continuous supply of oxygen to break down carbohydrates, proteins and fats, providing the fuel needed for sustained running. This covers a wide range of intensities, from a walk or talk at a tempo jog at an effort of 1-2/10 to moderate efforts where you feel like you’re working harder but are in control at an effort of 6-7 /10. The key to understanding aerobic intensity exercise is the ability to sustain effort for extended periods of time without becoming overly fatigued.
What is Anaerobic Exercise?
Anaerobic energy production depends on energy stored in the muscles at times when the body cannot produce enough energy aerobically. Anaerobic energy production is required for short bouts of higher intensity running or sprinting. Typically you will feel a rapid increase in perceived exertion (to 8-9/10 or higher), heart rate and respiration and you will be aware that you can only sustain the exertion for a short period of time before slowing down. To further complicate matters, anaerobic energy production is typically split into two systems:
The glycolytic system will provide a significant portion of energy in strenuous exercise lasting from about 10 seconds to about two to three minutes. Your body uses its stored glycogen to quickly create energy, but this does not last long and is accompanied by a rapid increase in fatigue and signs of fatigue (such as blood lactate).
The Creatine Phosphate (CP) system provides energy using creatine phosphate stored in the muscles. While this energy is delivered very quickly, it also depletes very quickly – usually it only takes about 8-10 seconds and then takes a significant amount of time to replenish. This system is used when sprinting, but also to ‘get going’ at the start of races.
What do these systems mean for your running?
Training that relies on aerobic energy production can be anything from short or long easy runs to what is commonly known as tempo or threshold training. If you want to increase the contribution of anaerobic energy production during a run, you will probably need to do so with some form of interval training where you work hard in short bursts and recover before repeating the heavy effort. The key to getting your sessions right is that the harder you work, the greater the percentage of anaerobic energy you need. As a result, you reduce both the amount of time you can run for that effort and the recovery you need between efforts.
Make smart training decisions
When structuring your training, there are a number of things to consider that affect the optimal balance between aerobic and anaerobic energy production:
Breed requirements: The majority of the races you are likely to run will require a very high percentage of aerobic energy. Even in 1500 meter races, about 85% of the energy contribution will come from aerobic sources. And the longer you go, the aerobic contribution increases.
Tip tip: Even during longer races if you are racing on hilly or uneven terrain, keep in mind that your body may have short periods of increased anaerobic energy production. The same also applies to races where you can have short peaks in the pace. To prepare for this, consider interval sessions or fartlek runs that combine short, fast efforts with longer, more steady intensity.
Intensity: At lower intensities your body can use a greater percentage of aerobic energy production, at higher intensities – especially past what is commonly referred to as ‘lactate tipping point’ – your body will rely on an increasing amount of anaerobic energy product to maintain your pace.
Top Tip: There are several ways you can monitor your running intensity. Some, such as heart rate, may be more useful for setting a limit on your aerobically focused sessions, while others, such as perceived exertion, timed splits, or strength, may be more useful for your anaerobically focused work.
Duration and scope: After a short period of high-intensity running, your body will quickly deplete its creatine phosphate and glycogen stores, so the longer you try to run, or the more reps you aim for at a high intensity, the more that will deplete your body’s fuel stores. is forced to rely on aerobic energy production.
Top Tip: If you want a higher percentage of anaerobic contribution in a session, you should use interval-based training with efforts typically two minutes or less for the glycolytic system and eight seconds or less for the creatine-phosphate system.
Recovery: The higher the percentage of anaerobic energy you expend during an interval session, the longer the recovery time between efforts to keep the session together.
Top Tip: An easy way to make an interval or fartlek session have more of an aerobic focus is to stick to very short recovery periods or continue to jog or run gently during your recovery periods. Conversely, if you want to run at intensities that rely on anaerobic energy production, give yourself a long recovery. I will often do eight second hill sprints with 2-3 minutes of rest.
fitness level: Runners new to the sport may have much less aerobic buffer before relying on anaerobic energy production.
Top Tip: Newer runners who focus on longer distances will generally benefit from a good period of time focusing on gentle running and more aerobic focused sessions before adding more anaerobic focused sessions later in their training.
A false dichotomy?
Everything seems relatively clear up to here? Well, we’re about to muddy the waters. It is important to understand that your body does not neatly separate aerobic and anaerobic energy systems. Instead, they exist on a continuum and work together to meet the demands of running. Both aerobic and anaerobic processes are active simultaneously, albeit to different degrees. Even during low-intensity running, anaerobic energy pathways contribute to total energy production. Similarly, during high-intensity anaerobic activities, the aerobic system continues to play a role in supporting energy production.
The false dichotomy between aerobic and anaerobic exercise often leads to a narrow focus on one type of exercise at the expense of the other. This approach overlooks the benefits that can be obtained from a more integrated exercise regimen.
An important reason why aerobic and anaerobic training should be considered complementary rather than mutually exclusive is their mutual influence on physiological adaptations. Aerobic exercise, with an emphasis on sustained effort, improves cardiovascular fitness, improves endurance and increases oxygen use efficiency. These adaptations, in turn, benefit anaerobic performance by facilitating faster recovery between bouts of intense exercise. Conversely, anaerobic exercise, which focuses on strength and power, can improve the body’s ability to generate force, leading to improved performance in both aerobic and anaerobic activities.
Embracing a more holistic approach to running allows for more versatility and flexibility in training. By incorporating a mix of aerobic and anaerobic dominant intensities, you can enjoy a more diverse and appealing plan. This variation not only prevents boredom, but also helps prevent overuse injuries that can occur from repetitive movements associated with focusing solely on one type of workout. It also gives you more physical tools in your arsenal.
Seeing the bigger picture
My mentor at Stirling University, Dr Andrew Kirkland, had a major influence on my thinking about training and coaching. Building on an article by Mark Hargreaves in the Jour journal Applied Physiology in 2008 Andrew argues that not only is there a false dichotomy, but thinking about your running in simple aerobic/anaerobic or “metabolic” terms is too simple.
He argues that there are many more factors to consider, such as muscle activation, psychology, fueling and even the social environment in which you run and race, which will have as much, if not more, impact than the training zone you use. and the associated splitting of aerobic and anaerobic energy.
It can be helpful to understand the terms, but focus on what’s important: good consistent training with a mix of different intensities, staying injury free and enjoying your run.
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