Aerobic vs. Anaerobic running. Do you know the difference?

Many runners are either unaware or unsure of the difference between them.

Understanding these two exercise states is essential to improving as a runner.

If you have set your sights on a PR at an upcoming race you need to understand these concepts.

They are are the core reasons why you can sustain a given pace for a period of time and why you can’t with others.

In addition to understanding aerobic vs anaerobic running we need to understand the role your body’s production of lactic acid plays into each running state.

Aerobic Running

Aerobic running is a state of exercise where your body has enough oxygen.

An example of this would be an easy run or a recovery run after a hard workout.

You can run without becoming winded and can sustain a conversation with your running partner.

In this state, your body has enough oxygen for your muscles to produce all of the energy required to perform.

Carbon dioxide and water are the two main waste sources through breathing during an aerobic running state and are easily expelled when you exhale.

Your body’s production of lactic acid is matched by your ability to use it as fuel and no excess is building up in your system during aerobic running.

Anaerobic Running

Anaerobic running is a state of exercise where your body does not have enough oxygen.

Think of when you may be going all out to the finish in a race or running very hard at a pace you can’t sustain for very long such as when you perform interval training.

When you are running anaerobically you will be unable to sustain a conversation with your running partner and will often be getting a few words out before gasping for breath.

Your body does not have enough oxygen to deliver to your muscles to produce energy.

As a result the energy has to come from somewhere to make up the difference.

That difference comes in the form of sugar. Your muscles will begin to burn sugar in addition to oxygen. One consequence of this is the over production of lactic acid.

You also enter an anaerobic state when you first start your run for up to 8-10 minutes depending on your fitness level.

Your body then transitions to an aerobic state assuming you are running a pace that is sustainable as discussed above.

This is the reason why you might struggle to get started at the beginning of your run and why it is often said “the first two miles are the worst miles“.

Lactic Acid

Lactic Acid is actually a good thing in the right proportions. It plays a crucial role in generating energy as you run.

The body produces lactic acid whenever it breaks down carbohydrates for energy. But like anything else, more is not always better.

Excess lactic acid is not easily removed from your body as carbon dioxide and water are.

Carbon dioxide and water can be expelled through your breath, but lactic acid excesses cannot. The result is lactic acid accumulating in your system.

The lactic acid itself is not the problem but rather one of the byproducts of your body producing lactic acid – Hydrogen. Hydrogen interferes with your body’s electrical signals in your muscles and nerves, slows your energy reactions, and impairs muscle contractions. Over a short period of time, this increased accumulation of lactic acid byproducts creates extreme fatigue.

The faster you go above your fitness level and thus enter an anaerobic running state, the more carbohydrates you will use fuel and produce lactic acid in excess of your body’s ability to use it or remove it.

It’s important to note that lactic acid itself is not the cause of muscle soreness nor the burning sensation you get from intense exercise. Muscle soreness stems from micro tears in the muscle tissue caused from exercise.

Real World Running Scenarios

If you start a training run or race at a pace that is too hard or increase to this pace in the middle of your run your body will enter an anaerobic state where lactic acid will accumulate in excess of your body’s ability to clear it.

If you enter this state too early in your run you will feel increasingly fatigued as lactic acid accumulates within your body and eventually you will be forced to reduce your pace to return to an aerobic state of running.

But herein lies the problem. Since your body has over produced lactic acid which has subsequently flooded your body your ability to increase pace or even continue at your planned pace is compromised. In a race situation, your goal time is now likely unattainable.

This is one of the reasons I consistently tell runners not to go out too fast at the beginning of a race or training run. Doing so jeopardizes the outcome of the entire activity.

Now you might be able to get away with running anaerobically at a very short distance race such as the mile. But you won’t be able to do the same over any considerable distance. In the case of the marathon this is even more critical.

The marathon requires that you run at a pace that is fast enough, yet not too fast that you prematurely burn your energy in the early miles. If you run anaerobically too soon in the marathon you will likely “bonk” well before the finish.

The goal is to conserve energy to make it all the way through at your planned pace and then run anaerobically into the finish if that is part of your race plan.