In my article, ‘Periodization: What Is It and Why Should I Use It?’, I mentioned that the Aerobic Base Phase is the most important phase of training. The reason is simple: the aerobic energy system supplies the foundation for all efforts in our sport. To develop a solid Aerobic Power Base, we must first define and understand it.
Understanding the Aerobic Base or Aerobic Metabolism
"Aerobic" refers to processes that occur in the presence of oxygen. When we use the term "Base" we are referring to the intensity level or power which can be generated predominantly by the Citric Acid Cycle, Tricarboxylic Acid Cycle (TCA), or the Krebs Cycle, named after its discoverer, Hans Krebs. While this system of often referred to as being less efficient due its higher reliance on oxygen compared to the anaerobic energy system, the aerobic system generates energy without the production of lactic acid. Also, efficiency is not usually defined by enery produced per O2 unit, instead efficiency is defined as energy produced per molecule of substrate. In this case, aerobic metabolism is more than 4 times more efficient that anaerobic metabolism. When using the term “Base” we should also be considering the extended and efficient production of energy over time.
When visualizing your Aerobic Base, think of it in terms of a highly efficient energy system that can be utilized for both duration and capacity. The duration represents the duration you can sustain a given pace ‘aerobically’, while the capacity represents the power or wattage that can be sustained aerobically at given intensities. A base of significant duration implies you can ride at a steady pace for long periods, while a base with significant capacity implies you can sustain a high-power output aerobically. Once the reliance for energy production shifts to being more anaerobic it is at this point that the clock is ticking and you are no longer aerobic. Optimally, you should be able to ride at higher power outputs for longer durations than you competitors. When aerobic system is optimized, it is what makes riding fast, easier for ‘fit’ rider.
The Role of Aerobic Energy Metabolism
Aerobic energy is the primary energy source in any endurance sport and is crucial in almost every cycling discipline. The bigger and stronger the aerobic system, the less anaerobic energy is needed at any given speed. In large part this is purpose of the base, to spare glycogen depletion through anaerobic energy metabolism. Since anaerobic energy is derived from glycogen stores and glucose it is quite limited and has a metabolic cost (lactic acid accumulation), riders with a strong aerobic system can conserve their anaerobic energy for critical moments in a race, while those with weaker aerobic outputs must tap into their anaerobic reserves at lower power outputs than their fit competitors. This will drain glycogen reserves much quicker in these athletes. So, the more aerobically fit athletes spare more glycogen than there less aerobically fit counter parts.
Developing the Duration and Capacity of Your Base
To develop the duration of your aerobic base, you must stay in the aerobic zone for extended periods. The exact duration is individual and changes with fitness levels. To determine your current base, you need to measure performance and perceived exertion. Power meters are particularly useful here as they measure continuous performance in watts and perceived exertion through heart rate (HR). By comparing wattage (performance) with heart rate (exertion), you can identify when you’re exceeding your aerobic base. Blood lactate measurements can help validate what is being seen in power and HR data.
When heart rate drifts above expected levels for a given wattage, you’re moving beyond the edge of your base, and this is where building duration begins. This is the point at which the system is stressed beyond its current capacity, leading to fitness gains when the stress is applied in the proper dose (frequency, intensity, and duration).
Factors Affecting Aerobic Base Workouts
Dehydration, poor air circulation (especially indoors), poor electrolyte balance, and inadequate refueling can negatively impact aerobic base workouts. Controlling these variables is essential for effective training. Proper hydration, nutrition, electrolyte replacement and using fans and adequate ventilation during indoor training can help ensure that the stress response being seen in the data is physiologic and not environmental (learn more about training indoors in my article entitled “Indoor Training – Is the Indoor Air Quality in your Training Center Runing your Workout?”)
As for the capacity of your base, or power output at aerobic threshold, athletes using power meters have a significant advantage. Heart rate users might inadvertently limit their progress by backing off intensity to stay within prescribed HR zones, potentially preventing the necessary over-reaching that stimulates adaptation. Over-reaching, unlike overtraining, is about slightly surpassing previous limits to encourage growth. Heart rate users need to be highly attuned to intensity and exertion to achieve similar results.
Pushing the Edge
How far past the edge should you go? This varies by individual. The key is to apply just enough excess load to stimulate adaptation without overtraining. A good starting point might be to ride 20 minutes past the edge at a consistent performance level (wattage for power users, gear plus cadence for HR users). However, this level of stress should not be applied every week—one long aerobic base workout per week is typically sufficient, though some studies suggest more frequent stress can be beneficial. The general rule is the more developed and fit the athlete the more training stress can be used with positive adaptation still occurring.
When to Move On
How long should you continue building your aerobic base? This depends on the law of diminishing returns. Eventually, the time and energy required to continue development may outweigh the benefits. If your base is sufficient to support your longest priority events, it may be time to transition to the Build phase. If not, more time and energy must be invested—there are no shortcuts.
Maintaining Your Aerobic Base
Once established, maintaining your aerobic base is simple. A workout of similar intensity and length to the level you’ve established, performed once a week, is generally sufficient.
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