Aerobic Base Training For Endurance Development

Aerobic base training refers to a specific phase of training where the primary focus is on the development of aerobic fitness, efficiency and conditioning.

It serves as a key part of any successful endurance program. In fact, many coaches and athletes consider the aerobic base phase—sometimes called the introductory, or foundational stage—to be vital for achieving peak endurance performance.

While aerobic base training is describes the foundational phase of an endurance training block; developing and maintaining aerobic fitness and efficiency is really a key part of all phases of endurance training.

In this article we look at…

• What is aerobic base training?

• The fundamentals and benefits of base training

• How to optimize and control low and moderate intensity exercise

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WHAT IS AEROBIC BASE TRAINING?

So, what is aerobic base training? And why is it important?

Essentially, aerobic base training is a phase of training where the primary focus is building a substantial level of aerobic “base” fitness.

It forms the initial phase of any endurance training block. In this way, it serves as the “foundational stage”, as it sets the support framework for subsequent training blocks. And specifically, for the more intense and event specific training that will follow in the later phases of training.

As such:

THE FUNDAMENTALS OF AEROBIC TRAINING

1. Focus on low and moderate intensities

During base training, most training should focus on low and moderate intensities. In fact, elite endurance athletes complete as much as 80% of their training at these intensities.

The rationale behind this approach is that by keeping most training at low intensities, you can build a larger foundation of aerobic fitness, reduce the risk of injuries, and improve recovery. And you are better conditioned for more intense and race specific training. We’ll inspect the benefits of base training shortly.

2. Training should be progressive

While aerobic base training often focuses on aerobic fitness and conditioning, the overall focus is not substantially different from other training phases. Rather, it’s the emphasis placed on certain key sessions that changes as we move towards the preparatory and competition phases. For instance, often there is a progression towards increased race pace training, or high-intensity interval training.

With base training, the progression takes the form of a gradual progressive increase in training volume, rather than an increase in intensity.

This should involve a gradual increase in weekly and monthly training volume. It should also involve a gradual progression in the volume of individual training sessions, such as your weekly long endurance run, or ride.

3. More base training = greater peak performance

The more emphasis you place on developing aerobic conditioning, the greater your endurance potential.

This can be understood by considering the training phases as a pyramid structure, with base training forming the base of the pyramid. And as you move up the pyramid, we increase the intensity.

When viewed this way, you can appreciate how having a wider base to the pyramid (greater level of aerobic conditioning) allows for a higher peak, or greater race performance level.

While there are several different approaches used to develop an efficient aerobic base, the primary emphasis is on developing aerobic fitness and conditioning.

The fundamental difference between approaches comes down to how much emphasis, a coach or athlete, places on other areas of performance—strength, power, speed, etc.

4. Intensity is still important

One important consideration is: successful endurance athletes still include intense training during the base phase. After all, if a training method works, why would you only use it during one phase of training?

While intense training should still feature, there is less emphasis on race specific training.

The key point here is:

while the emphasis may change during different training phases, you should include all key training elements within each phase of your plan.

In this way, it’s important to continue to work across a range of different intensities, including:

• Submaximal intervals,
• VO2max intervals
• Supramaximal intervals
• Sprint Intervals

5. Use this opportunity to develop strength

Besides building aerobic fitness, the base phase is often used to develop strength and conditioning. And with good reason: this is actually one of the best phases for endurance athletes to develop strength.

When we do this, we set ourselves up for greater long-term performance gains.

This can be through specific endurance focussed strength training such as hill repeats in running, or lower cadence cycling (including hills) during cycling, or using more traditional forms of strength training such as weights, circuits or core strength exercises.

WHAT ARE THE BENEFITS?

Using high-volume, low-intensity training, has several benefits, especially when combined with an appropriate amount of higher intensity and strength focussed training.

When done correctly, the benefits include…

1. Lower levels of physiological stress
2. Reduced risk of injury
3. Increased recovery from exercise
4. Improved exercise efficiency
5. Greater efficiency at using fat as a fuel
6. Increased training volume
7. Improved racing performance

1. Lower levels of physiological stress

In order for a training program to be effective, there needs to be a balance between training stress and recovery.

One feature of all successful training programs is a gradual ramping up of intensity, or training stress, across the training plan. Followed by a gradual taper, leading in to key events.

For this approach to be effective, it’s critical that athletes can adapt to the increasing training stresses.

With this in mind, the training stress must be sufficient to induce adaptation. However, it must not be too high to compromise recovery.

In this way, there needs to be a fine balance between training stress, adaptation and recovery.

One benefit is reduced levels of physiological stress. This allows you to build up the training stress, by carefully and progressively increasing training volume. And by accumulating the training stress, we achieve a much more consistent and progressive level of adaptation—helping to ensure that you are physically and mentally prepared for the next phases of training.

It also reduces the risk of injury, illness or over-training.

Often, we think of the base training phase as being all about logging miles.

The truth is: base training is actually more about consistent training. It’s about following a careful and systematic increase in volume. And achieving a gradual “controlled” level of progressive adaptation.

When you achieve this, you are better prepared and conditioned for the more physically challenging phases of training.

2. Base training reduces injury risk

Aerobic base training allows your muscles and tendons to adapt to training. In fact, a key objective during the aerobic phase is to strengthen your muscles and tendons by accumulating training volume.

Developing strength to reduce injury risk

Reducing injury risk is not all about developing conditioning through low-intensity training. In fact, developing strength in key muscle groups and tendons is one of the best ways to reduce injury risk.

So, how is this done during the base phase?

Sport specific strength training is vital

Developing sport specific strength is a key part of the base phase of training. So what does this mean?… Put simply, sport specific strength training refers to strength development that is specific to your sport.

Running specific strength training examples

If you’re a runner, then an important initial step is to include regular trail running. This has several benefits for runners:

• Helps to ensure that we develop different muscle groups,
• Increases recruitment of stabiliser muscles,
• It develops muscular conditioning and strength through increased eccentric loading.

I’ve covered this in greater detail in an article on the benefits of trail running.

Another option is hill repeats to develop running specific strength. Hill sprints are another great option for developing strength, power, running efficiency, and injury prevention.

While hill sprints are on the top end of the intensity spectrum, they should actually feature throughout your training block.

If you’re a cyclist, then you can look to include some lower cadence work, hill repeats, and short sprints.

Traditional strength training during the base phase

It’s important to include regular strength training to further strengthen and prepare your musculoskeletal system. While it’s common to emphasise strength training during the base phase of training; like all training types, this should feature in every training block.

With strength training during the base phase of endurance training, we normally place greater emphasis on strength development rather than power development.

This might involve greater focus on core strength, and fundamental exercises like squats, lunges, calf raises, etc.

That said, the base phase of training is actually one of the best times to develop strength and power. And many athletes report greater long-term gains by targeting strength and power during this phase.

3. Improved recovery after exercise

Another benefit is an improved ability to recover from low, moderate and more intense exercise sessions. The improved recovery and ability to cope with increased training stress may come in part from the way aerobic base training leads to improved muscular endurance and the efficient transport of oxygen and key nutrients to the working muscles (Martin and Coe, 1997; Neumann et al., 2000).

In addition, by developing the strength and durability of muscles, we also see an improved ability to cope with more intense training, and increased training volumes.

Taken together, this means you can train more effectively, and will see greater levels of adaptation as training intensity increases.

It also improves your ability to recover during more intense interval sessions.

What do I mean by this?… Here, I’m referring to the ability to recover during the rest, or recovery periods, of interval workouts. This allows you to train more effectively during these interval sessions.

4. Enhanced exercise efficiency

Aerobic base training is key to improving exercise efficiency. This occurs through a combination of:

• Type I (slow twitch) fibre development,
• Increased mitochondrial size and density,
• Improved blood flow and delivery,
• Increased efficiency of the heart,
• Improved glycogen storage,
• Increased levels of key enzymes.

And, not only does this lead to improved aerobic efficiency, it sets the foundations that allow you to utilise larger training volumes and higher training intensities.

As well as improving aerobic efficiency on a cellular level, we believe a high volume of low intensity training to condition and refine the recruitment of the specific muscles used during an activity.

This works in two ways:

• First, this can improve the efficiency of the recruitment of the working muscles.
• Second, it reduces the recruitment of antagonist and/or excessive recruitment of stabilising muscles (Fallowfield and Wilkinson, 1999).

Taken together, a high volume of low intensity training can improve efficiency on a cellular, and muscular level, and improve the co-ordination between specific groups of muscles.

5. More efficient fat oxidation

Another key feature is an improved ability to use fat as a fuel source. A key factor here is the intensity of training.

One point to note: elite athletes don’t typically increase the percentage of time spent in low-intensity training during base training. Typically, this would still make up around 80% of total training time throughout all training blocks.

What we see is: more of that 80% is at “easier” and “moderate” intensities, with less training time at steady, tempo and threshold intensities.

In this way, the training intensity is less demanding from a physiological standpoint.

Training at these lower intensities, especially when combined with longer duration training sessions, places increased emphasis on fat metabolism. Overtime, this can lead to improved efficiency of fat metabolism.

This can help to preserve valuable glycogen stores, both within training and during racing.

6. Increased training volumes

Not only does aerobic base training improve exercise efficiency, reduce injury risk, and improve recovery from training; it also prepares you for the greater demands of increased training volumes and the increased use of higher intensity training (e.g. Lactate threshold training, HIIT training), used during preparatory and race specific phases of training.

As mentioned earlier, we often talk about the aerobic base phase of training, as being the phase where we log all our big miles.

The truth is, the aerobic base phase of training sets us up for the larger training volumes, and the increased volume of high intensity training used during the later training phases.

A well executed aerobic base phase of training allows for both larger training volumes and an greater amount of threshold, and high-intensity interval training. This is key to successfully executing an endurance training program.

Why training volume is important

Success in endurance sport is not all about training intensity, a key ingredient of the most successful endurance athletes is the use of large training volumes.

To achieve such large training volumes, elite athlete complete most of their training at low intensities.

In fact, virtually all elite endurance programs share one core feature: 80% of their total training volume (sometimes higher) is completed at low and moderate intensities.

While low/moderate intensity training is unlikely to contribute to improvements in VO2 max in highly trained athletes (Acevado and Goldfarb, 1989; Londere, 1997); it’s a necessary factor in long-term development.

It also plays a significant role in developing the ability to sustain high percentages of VO2max, and for improving exercise efficiency (Noakes, 1991; Jones, 1998).

7. Improved endurance performance

As mentioned earlier, the development of a strong aerobic base is fundamental for success in endurance sport.

While this is difficult to verify through research, there are some case studies that provide insights it’s importance for long-term success in endurance sports.

From these, we can see that increased volumes of low-intensity, longer duration training (typically below 2mM blood lactate, or just below the first initial rise in blood lactate), appears to be an effective training method, leading to improved adaptations and endurance exercise performance (Seiler et al., 2009).

In particular, a large aerobic base fitness is necessary for the development of the lactate threshold, and the percentage of VO2max you can sustain during endurance events. It’s also a key factor in long-term development, improved exercise efficiency, muscular endurance and the efficiency of Type I (slow oxidative) and Type IIa (fast oxidative) muscle fibres.

In fact, aerobic training leads to a gradual transition in type II muscle fibres. When this happens, they take on many of the characteristics of type I fibres—to the point where, after several years of specific training, they become almost indistinguishable from type I fibres.

Summary of the Key benefits of aerobic base training:

• Increase in mitochondrial size and density
• Greater muscle capilarization
• Development of efficient aerobic energy systems
• Increased blood volume
• Hypertrophy of slow twitch (Type I) muscle fibres
• Increased amounts of red blood cells
• Enhanced free fatty acid metabolism
• Increased intramuscular fuel storage
• Improved blood flow to working muscles
• Increased cardiac size and output
• Improved muscular endurance
• Enhanced exercise efficiency
• Stronger more resilient muscles and tendons
• Lower levels of training stress
• Improved functioning of muscle fibres
• Lower risk of injury
• Reduced blood lactate levels
• Improved endurance exercise performance

OPTIMIZING LOW / MODERATE INTENSITY TRAINING

As we’ve seen, we primarily focus aerobic base training around low/moderate intensity training.

This raises two important questions:

• What’s the best way to control low intensity training?
• And what intensity is low and moderate?

First, we need to define what low-moderate intensity exercise is.

What is low / moderate intensity exercise?

At the most basic level, low-intensity exercise can be defined as an exercise intensity where there is a low level of physiological stress. Moderate intensity is one where there is a moderate level of physiological stress. We will look at this in greater detail in a moment.

What’s the best way to control intensity?

The three main options are:

• Heart rate
• Power
• Speed/pace.

Of the three options, heart rate and power are the most effective.

Heart rate monitoring

Heart rate is measured using a heart rate monitor—chest heart rate monitors are more effective than wrist based monitors—which provides a direct measure of physiological stress. Making this a great way to monitor the overall stress of a training session.

Using power to control intensity

While power has been widely used in cycling for many years, there are now devices like the Stryd footpod, that allow runners to make use of power.

So, why use power to monitor intensity? When we combine heart rate monitoring with power measurement, we get a more complete picture of training intensity.

So, why does power complete the training intensity picture? 

First, power gives you a direct measure of physical work rate (measured in watts).

Second, power levels can fluctuate substantially, even when heart rate remains relatively constant.

Power gives you an instant snapshot of your workrate, so you can adjust intensity, before a change in work rate has a noticeable physiological effect (increased heart rate).

In this way, monitoring both heart rate and power is extremely effective for controlling exercise intensity.

In summary:

• Power gives a measure of work rate
• Heart rate gives a measure of physiological stress

HOW TO CONTROL LOW / MODERATE INTENSITIES

Essentially, we have three options, with each providing a different level of accuracy.

1. A percentage of maximum heart rate
2. Percentage of heart rate reserve (Karvonen formula)
3. Percentage of estimated lactate threshold
4. Laboratory measured lactate threshold (LT1 and LT2)

Let’s look at the first option: the use of a fixed percentage of maximum heart rate.

Below are the most commonly used heart rate training zones.

1. Percentage of maximum heart rate

The first approach is to use a percentage of maximum heart rate. Below are the most commonly used heart rate zones based on percentages of maximum heart rate.

• Active Recovery (Very Light), 50-60% percent of MHR
• Endurance (Light), 60-70% percent of MHR
• Tempo (Moderate), 70-80% percent of MHR
• Lactate Threshold (Hard), 80-90% percent of MHR
• Aerobic Capacity (Very Hard) , 90-100% percent of MHR

So, why use heart rate zones?… By using heart rate zones, we can classify exercise based on intensity.

In this way, light exercise is often classified as being below 70% of maximum heart rate, with moderate exercise being between 70 and 80% of maximum heart rate.

One major problem with this approach is the zones are far less applicable to well-trained athletes.

2. Percentage of heart rate reserve

We can take this one stage further by also considering resting heart rate, using a method known as the Karvonen formula. In this method we first establish heart rate reserve (maximum heart rate minus your resting heart rate), we then multiply heart rate reserve by a specific intensity e.g. 70%. Finally, we add back on our resting heart rate.

While this method is more useful than just using a percentage of maximum, it’s important to remember that this is a guideline and doesn’t account for individual differences in fitness or conditioning. 

So, why do we also need to account for an individual’s fitness level?

You only have to consider how highly trained athletes can train and race at much higher percentages of maximum heart rate, to appreciate how the standard heart rate training zones become less useful as your fitness improves.

As an example, moderate intensity might be around 80% of maximum heart rate for a highly trained athlete. In contrast, 80% of maximum heart rate could be close to, or above lactate threshold, for a recreational athlete.

In this way, using a fixed percentage of heart rate is not always appropriate.

Another method is to establish training zones based on an estimation of lactate threshold.

3. Percentage of lactate threshold

We can also set training zones based on an estimation of lactate threshold heart rate or power (FTP). You can then set training zones, based on a percentage of estimated lactate threshold, FTP or race performance. You can also use time trials of field based tests to estimate lactate threshold.

One of the most straightforward tests is to complete a 30minute time trial, while recording heart rate and power. Your average heart rate, or power—recorded over the final 20minutes of the test—provides an estimation of your heart rate of power at lactate threshold. Another option is a cycling FTP test.

Below is an example of the training zones, based on a percentage of power and heart rate at estimated lactate threshold/FTP.

TRAINING ZONE	% FTP / LT Power	% FTP HR / LT HR
RECOVERY	<55%	<68% LTHR
ENDURANCE	56-75%	69-83% LTHR
TEMPO	76-90%	84-94% LTHR
THRESHOLD	91-105%	95-105% LTHR
VO2MAX	106-120%	>106% LTHR
ANAEROBIC	121-130%	NA
NEUROMUSCULAR	>130%	NA

Many athletes find this to be more effective than using standard heart rate zones. And it can make training zones more specific compared with using a fixed percentage of maximum.

4. Laboratory measured training zones

While we can use an estimation of lactate threshold, this is still just an estimation. And the only way to know with certainty is to measure lactate concentrations under controlled conditions.

From a scientific standpoint, low/moderate intensity exercise is classified as being exercise that is below the first initial rise in blood lactate. This is where a laboratory based lactate test can be really useful.

Laboratory lactate testing allows you to identify two key points:

1. The heart rate, power or speed where blood lactate levels rise above baseline levels (LT1)
2. The test also identifies the point where we see an accelerated increase in blood lactate levels (LT2)

From this we can classify 3 distinct training zones as shown in the image below.

• Low intensity (Zone 1): Blood lactate remains at baseline levels and doesn’t rise substantially.
• Medium Intensity (Zone 2): There is a “gradual” linear increase in blood lactate levels.
• High Intensity (Zone 3): Blood lactate levels accumulate at an increased rate.

Identifying the initial rise in blood lactate levels (LT1), allows you to better control low and moderate intensity exercise.

When exercising below LT1 (Zone 1), exercise is largely sustained by the aerobic metabolism of fats with only a comparatively small contribution from carbohydrate metabolism. Training within this zone allows you to complete large training volumes with a considerably lower risk of over-training.

Training in Zone 3 (above LT2), is also highly effective. And considered more beneficial than zone 2 training. 

Using this information, you can then optimise training intensity.

Using a polarised training approach

As I mentioned earlier in this article, most elite athletes complete 80% of their training at low intensities, with around 15-20% at higher intensities. And, they often base the intensities around LT1 and LT2; with 80% of training below LT1 (in zone 1), and a further 20% performed at higher intensities. 

Often, the higher intensity training is split so approximately 5% is in zone 2, and 15% zone 3. Although, this will vary depending on your training focus.

As an example, a marathon runner would accumulate more training time in zone 2, compared with a 10k runner. 

This approach to training—referred to as “polarised training”—is a very effective way to optimise training. 

So, by identifying these key training intensities, you can make better use of your training time, improve recovery rates and reduce the risk of over-training.

SUMMARY:

• Aerobic base training is primarily focussed on low to moderate training intensities—typically 65-75%HRmax (running), or 60-70%HRmax (cycling).
• At these intensities we mainly recruit slow twitch (type I muscle fibers)
• A large portion (>50%) of any endurance based training programme should involve aerobic base training. And most elite endurance athletes devote 80% of total training time to these intensities.
• It has several advantages including: 1) reduced levels of physiological stress; 2) lower risk of injuries; 3) improved post exercise recovery; 4) enhanced exercise efficiency; 5) improved efficiency of fat metabolism; 6) allows larger training volumes; 7) leads to improved exercise performance. 
• This helps to condition the body for the physiological demands of higher intensity training.
• The relatively low intensities used during aerobic base training allow athletes to complete large training volumes, with a reduced risk of over-training, compared with higher intensity training (>LT)
• A large volume of aerobic training is important for the development of the lactate threshold, exercise economy, fatigue resistance, mitochondrial size and density, and enhanced aerobic energy pathways
• Low and moderate training is best controlled using heart rate or power.
• We can control training intensity using a percentage of maximum heart rate, percentage of estimated lactate threshold, or laboratory measured lactate values.
• Laboratory testing is very effective, allowing you to control training based on the relationship between intensity and blood lactate levels.
• A polarised training approach—involving large volumes (80%) of low intensity training, combined with 15-20% of higher intensity training—is very effective.