The Runner's Guide to Aerobic Base Building

Zone 2. Maffetone. Long slow distance. If you're a runner and you've dabbled in endurance training, you've likely encountered one of these philosophies. What they all have in common, aside from encouraging you to run painfully slow during most of your training, is that they're all targeted at building the "aerobic base." 

In this article, we'll explore the concept of an aerobic base, differentiate between aerobic and anaerobic running and provide insights into how to build your own aerobic engine.

What Is An Aerobic Base? It's All About the Oxygen

Imagine your body is a car. If your legs are your tires, your aerobic base is your engine. The aerobic base is the foundation of your cardiovascular fitness and endurance as a runner; it's what powers the whole operation. 

Colloquially, when runners talk about their aerobic base, they're referring to the level of efficiency and strength of their aerobic energy system. This system primarily relies on oxygen to produce energy during exercise. The word aerobic comes from ancient Greek, where "aero" means oxygen and "bios" means life. As such, aerobic-based exercise means that your body requires oxygen to give life, or energy, to your movement.

The more developed your aerobic base, the better your body becomes at using oxygen efficiently to sustain prolonged effort. This is why elite runners often run 100+ miles a week during peak training season. By building a solid aerobic base, they enhance their body's ability to supply oxygen to working muscles, burn fat for fuel, and maintain a faster pace for longer durations. Over time, this strategy helps runners at levels run faster and farther at a lower level of perceived effort.

Aerobic vs Anaerobic Running: Oxygen vs Glycogen

Aerobic adaptations happen when your heart rate is in a specific range, which for most people is between 60% and 80% of their max heart rate, or alternatively 55% to 75% of vo2max. This is why there's such a focus on zone 2 training in most structured running plans—this corresponds to the aerobic base-building sweet spot. The exact target heart rate for zone 2 differs based on the program you follow. For example, legendary coach Jack Daniels who pioneered the Vdot-based training system prescribes 65% to 79%.

On the other hand, anaerobic means without oxygen (the an- prefix means not, and aerobic means with oxygen). When you do higher-intensity training, you put your cardiovascular system into an anaerobic state, meaning it's using an energy source other than oxygen, as the demand for oxygen has surpassed your body's ability to supply it. When you're in an anaerobic training zone, your heart rate is usually 80%+ of your maximum, and your body is pulling on glycogen stores for fuel rather than oxygen. In an anaerobic state, you'll slow down eventually when your body runs out of glycogen. In marathons, this leads to the phenomenon known as "hitting the wall" (slowing down significantly midway through the race) and is why a negative split strategy where you start out slower and speed up through the race is most effective—it keeps your body in an aerobic state for as long as possible.

How to Build Your Aerobic Base: 5 Foundations of Endurance Training  

The best way to improve your endurance and up your best race times is to build your aerobic base. Here are five keys to help you get there.

1. Staying Consistent Over Weeks, Months and Years 

Here at Supwell, we like to say that the three rules of running are consistency, consistency, consistency. There's no shortcut to aerobic base building, other than consistency, compounded over time. To start, you should run roughly 80% of your weekly mileage in zone 2 and aim to increase your weekly mileage over time. Once you're comfortable with the level of mileage you're running—and if you've remained injury free—increase your mileage by 5% to 10% each week (or up to 20% if you're a more experienced runner). 

2. Maintaining a Weekly Long Run 

Long runs are a prime opportunity to build your base, as you'll be flexing your aerobic power for the longest period of time. Ideally, your long run should be at least two hours if you're training for a marathon to give adequate time for cardiovascular adaptations to happen (90 minutes if you're training for a shorter event). Make sure that you're fueling well before, during and after the run, so you can keep undue stress on the body low.

3. Doing Tempo Runs at Aerobic Threshold Pace

Tempo runs, when executed at the correct pace, can help improve your aerobic threshold, which is the point at which your cardiovascular system switches from using oxygen to burning glycogen stores. Because oxygen is freely available and glycogen is not (there's a finite amount stored up in your body), you'll run out of steam quicker when you cross the aerobic threshold. Running at this pace trains your body to push that threshold outward—i.e., helping you run faster with less effort.

For maximum benefit, tempo runs should be done at your aerobic threshold pace, which can be found using the VDOT training calculator. Once you're comfortable with your baseline mileage level, you can include one or two tempo runs per week, gradually increasing the duration or distance. These type of sessions shouldn't take up more than 10% of your weekly mileage.

4. Cross-Training To Get Extra Aerobic Base Building Time

Engaging in low-impact aerobic activities like cycling, swimming, or rowing can complement your running routine and promote aerobic fitness without excessive stress on your joints (this can allow you to "steal mileage," i.e., build up your aerobic fitness quicker than you would have with running alone). You can convert the time spent doing aerobic cross-training to running mileage by considering every 10 minutes of non-running activity as one mile.

5. Staying Healthy By Prioritizing Nutrition, Strength Work and Recovery

Consistency is the name of the game when it comes to building a robust aerobic engine, and you can't be consistent if you're hurt. The best way to prevent unnecessary injuries is to be conservative with increasing your mileage, stay on top of your nutrition, hit the gym to strengthen your core and stabilizing muscles and roll out after runs with a foam roller or alternative recovery tool. 

Bonus: Running At Anaerobic Threshold Pace

Another way to improve your endurance, though not necessarily your aerobic base, is to run at  anaerobic threshold. This pace range helps your body get better at clearing lactate, the acid that builds up in your legs during hard efforts. Running consistently at your anaerobic threshold will improve your overall efficiency, which will help make your race paces faster.

How Long Does It Take to Build An Aerobic Base?

The beauty of the sport of running is that you can do it until your legs no longer work. As such, the work of aerobic base building is never really done. However, the time it takes to build an aerobic base that's sufficient to be used as a prerequisite for more intense training (i.e., starting your first marathon training program) varies depending on your starting fitness level, training consistency, and genetic factors. Generally, it takes several weeks to a few months of consistent aerobic training to see gains in your aerobic capacity.

Final Thoughts

Remembers the three rules of running? Consistency, consistency, consistency. Building an aerobic base takes time. While it's our birthright as runners to madly dash to the finish line, this is a case where it's about slow and steady over the long game (you know that saying about the marathon and the sprint… and the story about the tortoise and the hare). Gradually increase mileage, commit to a weekly long run of at least 90 minutes, prioritize recovery and—most importantly—trust the process.