Training Science Series #6 - The Aerobic Base - Capacity Training 101

You may have heard athletes refer to other athletes as having a really “big motor” or a fantastic “aerobic base”. What does this really mean? Having a big motor allows you to handle more training volume, and as a result, maintain higher speeds for a longer amount of time than other athletes.

Training Science Series #6 - The Aerobic Base - Capacity Training 101

You may have heard athletes refer to other athletes as having a really “big motor” or a fantastic “aerobic base”. What does this really mean? Having a big motor allows you to handle more training volume, and as a result, maintain higher speeds for a longer amount of time than other athletes.

This is an article series designed to help further educate my Performance Coaching clients, but also anyone interested in learning how to train more successfully. If you are interested in getting fitter -- irrespective of whether you are a novice or regular athlete -- then please read through this series and learn more about the endurance training process. I also hope to welcome you onboard as your performance coach one day if you need mentoring to reach the summit of your athletic potential!

Understand the Process to Commit 100% to the Process


You may have heard athletes refer to other athletes as having a really “big motor” or a fantastic “aerobic base”. What does this really mean? Having a big motor allows you to handle more training volume, and as a result, maintain higher speeds for a longer amount of time than other athletes. The big motor refers not only to the cardiovascular system, but the capacity of slow-twitch muscle fibers. The way to get there is not through a mountain of utilization training, but a high volume of low intensity capacity training. Hours upon hours, month upon month, and years upon years is how to build the best performing aerobic base. So, repeat after me: “I will never achieve my endurance potential without maximising my basic aerobic capacity first.”

The most important physiological adaptations to lower-intensity capacity training are structural, inducing multiple adaptations across various metabolic systems. As training volume increases your body begins to grow new protein structures, increasing the qualities of the slow-twitch muscle fibers and their sustainable metabolic output. The outcome is denser capillary beds in the trained muscles, increased mitochondrial mass, and changes to the heart. The dense network of capillaries in the skeletal muscle, is where oxygen transfer into muscle occurs, and this is what ultimately maximises endurance performance. No level of high-intensity training provides those metabolic or structural adaptations because these metabolic adaptations occur in the slow-twitch muscles fibers, which are not conditioned at higher training intensities. A high focus on utilization training means the low-power slow-twitch muscle fibers simply do not get enough training stimulus for these adaptations to occur. You can only induce these responses by training frequently at low-intensity.1 Also, when you run slower, your injury risk is lower, allowing you to run more frequently, thus increase your overall volume of km’s per week.

These metabolic changes are really really slow to occur and take months to show any significant development. They also continue developing for many years. This is one reason endurance athletes often have very long careers, continuing to improve even into their 40’s. Most importantly, an endurance athlete can never have so much aerobic capacity it becomes detrimental to performance. Each year can build upon the next until only old age as the factor that starts to limit an athlete’s progression upward.

It is often said that most people are 5-7 years away from their athletic potential once they begin a properly designed endurance training program.2 This timeframe is often not super appealing to athlete’s starting out who want to see immediate results from pushing hard all the time; however, there is no escaping reality. Just like it takes a decade or more to master any skill in life, the same applies in endurance sports – slow and steady wins the race and the athletes who invest the most time, get the most out of it.

Therefore, capacity training mentality should be less focused on going fast, but enhancing these specific metabolic processes. Unfortunately, this means an athlete may be forced into going slower than they might prefer, for really long periods of training time. However, by going slow, they can basically train more over the course of the year, which is required for these adaptations to occur—that is the trade off. Ultimately, the goal should be to remain healthy and fresh while slowly incrementing the level of training each month (modulated with rest weeks). This minimises the chances of injury and fatigue as the level of training volume steadily increases from year to year. Furthermore, training intensity should only increase when an athlete is handling the present volume successfully and there are ways to test when an athlete is ready for this (as will be discussed later).

For effective capacity training, you must have a plan you work from, and a training log to record your process. Kilian Jornet has recorded every single activity in a training log since he was a teenager. He explains:

By logging his training, Jornet can look back on each year of training and this helps him to ensure the next year was a little harder than the last—allowing him to safely increment his volume to astoundingly high levels. Without all his training information logged he could never really know for sure if what he is doing is too much or too little, nor how to structure his training appropriately and when he needs to back off and rest. As he mentioned, he can also look back on races where we optimally performed and start to understand the types of workouts that produced better outcomes. This means his preparation for races always improves, underlying why his winning consistency is so high—because he keeps learning from his mistakes.

Many people assume high-volume – and not high-intensity – is the underlying cause of burn-out in endurance sports. It definitely can be when high volume training is executed by someone who is not conditioned for such volume. However, high-volume training with too much time at higher-intensity is predominantly the major problem. This is obvious when you think about it. The imposition on overall fatigue can be enormously different when we compare the same 100km or 100-mile training weeks performed averaging either a heart-rate <120bpm, versus the week averaging heart-rates much higher. It’s not necessarily how much you do, but how hard you are training, that matters more.

When determining whether an athlete’s training volume is careless or appropriate, one must consider how long the athlete has been training at such volume and how they got there. For one athlete it can definitely be careless, for another it can be appropriate.  An athlete can safely progress to high training volumes through a long period of low-intensity capacity-building over a number of years. Kilian Jornet now trains around 1300 hours with almost 500,000 meters vertical accumulation per year. This is one of his big advantages over other athletes. This big aerobic motor from years of capacity training allows him to handle more volume and – subsequently – more utilization training than other athletes can manage.

Metabolic adaptations from capacity training are the reason why you don’t have to frequently train at the pace you aim to sustain for long-periods in a race. For example, in endurance sports, no one successfully trains for a 100-mile ultramarathon, by running 100-mile training days before the event. Nor do Tour de France cyclists train for the intensity of a high-volume three-week race by training with the same intensity and volume of the event, prior to the event.  An athlete can best prepare for the demands of an endurance event by slowly progressing up to a high-volume of weekly capacity training closely matching the demands of the race. For example, a 100-mile race should have a few weeks totalling 100-mile in distance prior to the event (although that’s not a set rule and some athletes get by with far less).

These adaptations also allow you to run at faster paces using less fuel over time. It is possible to get really fast through years of only base training alone, but that wouldn’t be all that fun, so the effective application of utilization training periodically can peak an athlete for racing, and encourage greater fitness adaptations before recommencing further base training each season.

Other enormous benefits of low-intensity capacity training involve increases in your body’s fatigue resistance, movement economy, and recovery rate. All these components are highly trainable and improve solely from a lot of low-intensity training volume.

Fatigue is essentially your body becoming tired due to its inability to meet the energy demands of the exercise. The more you are active, the more fatigue resistance you develop to being active. The number one aspect that limits endurance is fatigue, which manifests for runners as a slower and more reduced stride length. A lot of capacity training helps to train your body to adapt to the demands of running. For beginners, at first, running can feel difficult and tiring, but after several weeks, running starts to feel easier. After a while, you can run effortlessly and go home feeling refreshed rather than exhausted. What is occurring under the hood is your aerobic metabolic system is beginning to upgrade itself.

Movement economy combines two components: technique and metabolic adaptations. Good technique involves the efficient use of energy needed to move at a specific speed. Without going deep into the science, basically, the more you run, the more efficient your body becomes at running. This is why when you watch a running race, the elites effortlessly glide past looking like barely tired gazelles, while the back of the pack runners are a sorry sight of many flailing limbs. The elites didn’t get this way doing a lot of technique drills, they simply ran a lot. Technique improves over time, and a lot of climbing (stairs and uphills) can really help to automatically develop proper running form, without too much focus on drills (that people rarely like to do and may barely help anyway). Technique seems to iron itself out over time, so volume and a lot of vertical hill training (which forces better technique) is the best way to improve running technique in my experience (sorry to those who place more stock on it).

Metabolic economy involves metabolic pathways our muscles use to produce energy required to sustain various intensities. With a big aerobic capacity, the ability to rapidly recover from the increased demands of utilization training, will be quicker. Increased (and impressive) recovery rates are one of Kilian Jornet's biggest advantages over other competitors as well. His astonishing rate of recovery from training loads and races means he bounces back to regular training quicker than most other people can even imagine. He can run—and win—a 100-mile one week, and one or two weeks later, win another race, all while continuing to train in between. Meanwhile, it can take other people a month or more to bounce back from a 100-miler.

The best way to conceptualise the difference between capacity training, utilization training and overtraining syndrome is to think of what it takes to build a bonfire from a pile of kindling. An athlete with minimal capacity is like this small amount of tinder (see figure-3).


Figure 3 – Minimal Aerobic Capacity

Utilization training for an athlete with such a small aerobic base would be like pouring gasoline on this small pile. You get a one-time fast burn, maybe you can add a few small sticks to it, meanwhile it burns hot and quick, and within a short duration there is nothing left but a small pile of ashes. There wasn’t “enough time” to place any wood on top, nor to go get it to burn for a long time. Also, every time you want to light a fire, you are stuck lighting it from the same starting place, an empty fire pit. If you wanted to maintain the burn, you have to keep dripping small amounts of gasoline on the fire regularly, but eventually any tinder in the piles burns up into nothing and you’re left trying to pour gasoline on a pile of ashes. You may also just run out of gasoline too, since the tank is not an endless supply of fuel.

Building the aerobic base starts with a small pile of tinder and then kindling placed on top (See Figure-4). Each year building your aerobic base through capacity training builds upon the previous year like adding more and more sticks, and then eventually logs, to build a larger fire (See Figures 4-6). You cannot place a massive log on a small fire otherwise it collapses under the weight. You must incrementally add appropriately sized logs, waiting for them to ignite and burn for a while, before they can support the weight of any larger logs that will eventually burn for much longer.

An aerobically developed athlete has a strong long-duration burning fire, and each training month places one more log onto the fire. Even though some of the logs are burning away, adding more logs keeps slowly increasing the size of the fire, thus the overall heat produced by the fire (higher performance). Even if training stops (no logs added), the fire still burns for a long-time. Slowly the fuel and heat diminish, but can be reignited anytime by adding more logs back onto the fire to rebuild it back up rather quickly.

Really big thick logs are like heavy volume of low-intensity training for an elite athlete. When you put a big log on a well-established fire, they burn for a really long time while producing a lot of heat. You can pour some gasoline on the fire if you like (utilization training) to temporarily increase the heat and force the fire to burn more fuel quickly to warm everyone up (supercompensation), but even with some of those logs burned up a little quicker, we’re still left with a strong well performing fire.

You can keep adding logs and turn it into a bonfire if you like (more year’s capacity building). The size of the fire just keeps increasing and increasing with no real limit each year. You just need to keep adding more and more logs. Eventually, a limit will be hit, but it depends on how wide the foundation of the fire was built with (years trainng). In this analogy, Kilian would be like the bonfire at Slinningsbålet (Figure-7).

Figure 4 – After a year of Capacity Training

Figure 5 – Another Year of Capacity Training (Thicker pieces of wood can now be placed on top of the existing base capable of supporting the weight of those bigger logs)

Figure 6 – Aerobically Developed Athlete (Long, slow, consistent burn)

Figure 7 – World Class Aerobic Capacity in Race “Beast Mode” (Slinningsbålet the world’s biggest bonfire).

Fatigue is like the sprinkling of rain that temporarily diminishes the burning capacity of a fire depending on how much water is falling. Small amounts do very little to extinguish a fire, and the bigger the fire is, the more it can handle heavier rain. However, even a bonfire can be extinguished if the rain is heavy enough and for long enough. Overtraining syndrome is when the fire burns out completely from the rainstorm, all your wood is wet and your matches are drenched. You won’t be able to reignite the fire immediately, you now have to wait for the rainstorm to pass, and then for the wood and matches to dry out. All you can do is wait and wait. Also, you can’t reignite the big logs anymore either, now you have to go back and start with a small pile of kindling, make sure that is burning well, before you add on a few more sticks, then eventually you can start adding logs to the fire again. Because you’ve built the fire before and have a large fire pit established, you can build up the fire again faster with your prior experience. Maybe you can build a big bonfire again, maybe you’ll be more conservative and just be happy with a smaller fire to keep you warm and cosy. If you’re smart enough you check the weather regularly (a more appropriate training strategy) so the weather doesn’t put out your fire again.

Finally, a common complaint from athletes is they don’t have the time for high volume of training and prefer the benefits of short higher intensity training. If you cannot commit the time to building a strong aerobic base, you won’t become the best athlete you could be, but that does not mean you cannot be a strong athlete. If your training is only possible due to falling behind those other priorities in life, then certainly adding intensity will improve your fitness quickly, but only temporarily. If you choose the utilization training approach, then the trade off will be that you must add more rest to recover from the intensity of the training load or powering on. The only way to add more rest is to reduce the bulk of low-intensity training or remove it completely, therefore your aerobic capacity will reduce, rather than increase. If you power on without adequate rest, then OTS is on your horizon. With more utilization training you just need to be smarter about how you train and know your limitations as an athlete.

Unfortunately, without a strong aerobic base underpinning fitness, you will never maximise your fitness potential. Any potential benefit from high-intensity training is directly proportional to the size of your aerobic base and that is unavoidable—there is no shortcut or way around it. The amount of time spent building the aerobic base will become the biggest factor in reaching your overall potential as an athlete. 

Next Article -> Part Seven - The New Science of Fat Adaptation


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