Build and Turbo 💥 charge your 🚴🏻‍♀️ Aerobic Engine 🚴‍♂️

Cycling is predominantly an aerobic sport and the primary objective of any training plan should be to build and improve the aerobic energy system. But what does aerobic mean?

Aerobic describes activity that involves or requires oxygen. In aerobic activity, energy is produced from glucose metabolism using oxygen. Everyone has an aerobic capability to inhale, transport and utilise oxygen to sustain periods of aerobic activity.

The simple objective of aerobic training is to decrease the oxygen demand for a given level of sub maximal exercise, and increase the ability to use oxygen to produce energy to power more forceful muscular contractions.

Aerobic training is therefore primarily about improving the functioning of your respiratory and cardiovascular systems, lessening the demand on these systems to produce more power.

Building your aerobic engine involves improving the ability of your heart, lungs and vascular system to deliver oxygen to your muscles, to become more efficient at producing energy to power pedal revolutions.

Building your aerobic engine results in you becoming more efficient, using less oxygen to produce more power. A reduced heart rate for a given level of work.

In the chart below we are plotting a rider’s efficiency by dividing their average normalised power by their average heart rate. As you can see over the course of a season this was trending positively. This rider was producing more power per unit of oxygen consumption.

Over a longer time horizon, we can see how this efficiency ebbs and flows during multiple seasons and also how it improves over the whole 6 year training period, starting at 1.38 in 2014 and now scoring 2.00.

To simplify and put that into plain English, this rider was producing 200w at a heart rate of 145bpm. He is now producing 290w for the same 145bpm. That’s a pretty decent aerobic engine development.

Developing your aerobic engine is challenging. Not because it is hard per se, but because it takes a lot of time. The developments at a cellular level happen gradually and slowly. As can be seen above, the improvements take years to develop and require dedicated and disciplined training. Most amateur riders try and train their aerobic system at too high an intensity and don’t, or can’t, dedicate the time to ride at an intensity that deliver the best aerobic adaptions.

There is a lot of heated debate about how to train the aerobic system most effectively. Forgetting for a moment any practical limitations on your time, the fundamental principle of aerobic training, in fact any training, is the concept of progression over time.

Remember that at any level of intensity you will be driving some aerobic benefit so to train the aerobic system you could adopt any of the training approaches below:

  1. High volume & low intensity training.
  2. Medium volume, higher intensity training.
  3. Low volume, high intensity training.

I do not believe that there is one system to suit everybody or that should be used in isolation. People react differently to different types of training stimulus at different times of their training cycle, and have varying amount to time to train in.

I do fundamentally, anecdotally and personally believe that the foundation of developing a powerful aerobic engine is spending most of your training time at a relatively low level of intensity, for increasing amounts of time, focusing on individual progress and development.

My fundamental Principles of Aerobic Training

  1. The primary building block of building better aerobic fitness is low intensity training. Building a depth of fitness from below by progressing training time, not intensity. This is not to say that all training has to be low intensity, far from it, but your focus should be extending the duration of your long endurance rides.
  2. Once this fitness depth is in place, you can improve your aerobic capability by increasing the amount of training at higher intensities, driving the aerobic system higher, through workouts demanding high power, progressing training intensity, not time. During this time, you should continue to include rides at a lower, endurance intensity to maintain your depth of fitness.
  3. This push from below and pull from above work together to both increase the size of your aerobic engine and its performance. It develops more capacity and a better turbo charge.

Tracking Progression and Improvement

As with any type of training you will witness diminishing returns over time so how do you track your progression.

Tracking your Efficiency Factor is a great place to start. As highlighted above, and in the graph below, you should see a gradual improvement in the power/heart rate ratio over time. If you don’t have a power meter, you can track your speed/heart rate on a route that you ride regularly. If you notice that your average heart rate is decreasing for the same given speed, or you are going faster for the same average heart rate, then you are becoming more aerobically efficient and have improved your engine.

If you are using power, you can also track how heart rate and power correlate during a ride. When you are less fit you would expect your heart rate to gradually increase, or power to gradually decrease as the duration of your ride increases. This divergence of power and heart rate is called decoupling. As aerobic fitness improves you should see less decoupling of heart rate and power over increased durations of riding.

Both efficiency and power – heart rate (pw:hr) decoupling can be tested on a fully aerobic, steady state ride. Find a route that is flat to undulating and aim to build intensity so that your perceived effort is around 4/10. This should not feel too hard, nor too easy. Now ride for 60-90 minutes the first time you do it and keep that level of perceived effort at 4/10 level. At the end of the ride you can check to see how your power behaved relative to heart rate.

In the example below you can see that this rider rode at a steady average heart rate of 135bpm (which for him equated to a 4/10 perceived effort) for just over 90 minutes. Variability was low indicating a nicely paced ride. Efficiency was 1.59 which we calculated by dividing normalised power of 215w by average heart rate of 135bpm.

You can clearly see here how power (yellow line) fell away gradually over time, decoupling with heart rate by 7.24%. Not a disaster but not great over such a short duration.

Fast forward 12 weeks and this same rider rides for nearly 4hrs with a 7w increase in power for the same average heart rate, resulting in an improvement in aerobic efficiency to 1.66. Power heart rate decoupling was now 4.98%, indicating a great level of aerobic fitness.

Over the course of your training year your efficiency will hit a natural ceiling level. Once reached, the gains to be made by increased aerobic training are limited and an endurance maintenance program can be put into place.

In very general terms it will take around 4-5 months to hit this upper level of aerobic performance. After 1-2 months of aerobic training, with gradually increasing duration, you will be around 65% adapted vs your absolute potential. After 2-3 months you will be around 85% adapted and after 4-5 months you will be around 95% adapted. This gradual decline in improvement velocity is what we mean by diminishing returns. It takes more time/effort to harvest smaller improvements.

In the table above we can see how this rider improved his efficiency from 1.56 at the start of the 2017 season, gradually improving each month until April, the date of his main event at Mallorca 312. Having worked with this athlete for a while we knew that around 1.95 was his upper limit so once efficiency started to hit 1.85 we started to change the focus on his training to elicit further gains in fitness.

We can use pw:hr decoupling during a long ride to determine at what stage, if any, did decoupling start to happen. We can also use this metric to determine where there was a real degradation during interval training. A rapidly increasing pw:hr ratio would indicate fatigue, so understanding where this is happening allows us to prescribe more individual workouts based on a rider’s specific fatigue profile.

The human body is extremely complex, far more complex than many of us realise. Almost everything you read, including this article, is a gross simplification of what is actually going on at a cellular level in our bodies. However, we now have some pretty cool software, metrics and analysis, to help us understand the relationship between training and improvements in fitness and to prescribe workouts on a very individual level.

In summary, to build a big aerobic engine you need to start by building a depth of fitness with plenty of aerobic training in the lower zones. Progressing time should be the primary driver. Once you have a solid level of aerobic fitness, as quantified by your efficiency factor and pw:hr decoupling, then you can increase the dose of higher intensity workouts, driving your aerobic system higher by progressing training intensity. This push from below and pull from above will increase your aerobic capacity, threshold power and stamina to give you more capacity and improved turbo charge.