Understanding the Lactic Acid Threshold and the Role It Plays in Endurance Training

Ever wonder what that “burning” sensation is when you’re running a 5k or marathon? You know, that burn you feel in the middle or near the end of the race? And when you try to run faster, it gets more intense, so you end up having to slow down?

It’s super frustrating, right?? If it weren’t for that burn, you’d be able to finish strong at the end of every race...

Well, at least you’re not alone in the excruciating final stretch — that burning feeling is extremely common for runners. Even better news is that it’s also extremely avoidable (if you train the right way).

There are a few specific modifications you can make to your training that’ll delay that achey burn, ultimately helping you to run faster and for even longer distances! 

The key lies in your body’s production of lactic acid and your ability to train your lactate threshold for the most efficient running. 

Don’t worry if you’re not familiar with either; that’s what we’re here for.

What is Lactic Acid?

Lactic acid is a byproduct that our bodies produce as an additional source of energy. When you’re working out, your muscles require a whole lot of energy, and your body uses oxygen as its main source of energy (known as aerobic energy). But when workouts are really intense, your body isn’t always able to produce enough energy just through oxygen alone — and that’s where lactic acid comes in.

If it sounds complicated, that’s because it is (and that goes extra for the first time you’re reading about it). Without getting too academic and particular, here’s the science behind using lactic acid for energy.

Imagine that you’ve been running for a while, and you’re reaching the end of your aerobic capabilities (your body has run out of the capacity to use oxygen for energy). 

In order to catch up to the demands of intense exercise, your body will produce lactate (otherwise known as anaerobic energy). Using lactate as an energy source doesn’t require oxygen for the conversion process. Unfortunately, it’s easy for excess lactate to build up in your bloodstream because your body often produces it more quickly than it can use it. 

This excess lactate creates its own byproduct of hydrogen ions that make your blood more acidic, making it harder for your muscle fibers to contract properly. As a result, you’re more prone to muscle fatigue and that all-too-familiar burning pain as you run.

Which is pretty frustrating, considering your body was only trying to help you out — it just tries too hard, sometimes.

So, instead of letting your body’s “good intentions” overpower you, you can prevent lactic acid build up by training your lactate threshold.

What is a Lactate Threshold? 

Don’t worry — it isn’t as complicated as it sounds.

Your lactate threshold is essentially the fastest speed that you can run that allows your body to produce and clear out lactate at an equal rate, keeping your blood lactate levels steady (Magness, 2014). It indicates the point where your body switches from using aerobic to anaerobic energy.

lactate thresholdIf you’re running at a lower intensity, you’re training under your lactate threshold because your body is still able to use oxygen as its primary source of energy. But, once your body hits the point where it needs to rely more on lactate for its energy, you’ve started training over your lactate threshold — the image to the left represents how quickly your lactate levels increase when this happens. 

As you can see, at rest, there is minimal lactic acid production, but as the runner begins to pick up pace, the lactic acid begins to build up. Once the runner surpasses a certain intensity, the lactic acid spikes to unmanageable levels. 

Ultimately, the goal is to hit your lactate threshold and maintain that speed without tipping the scales in favor of excess lactate production. That way, your body will be able to train at high intensities for a longer period of time without feeling the burnout. 

It’s key to remember that your lactate threshold is more impacted by intensity, rather than by running pace. Someone can run an 8-minute pace and feel fine, but if they were to try to keep that same 8-minute pace during an uphill portion, they would fatigue sooner because they’re training at a higher intensity.

Most major coaches and exercise physiologists understand how important lactate threshold is for distance runners — it’s an important facet of training for any race distance greater than 400m, and it becomes even more essential over longer distances. 

But, in order to achieve this magical running speed and efficiency, your body’s going to need some practice to properly gain that kind of control. 

That’s right — as with most improvements in running, there’s more training to explore.

How to Train Your Lactate Threshold System

It’s interesting that you can actually train your body into being more biologically efficient — it’s almost strange to think about.

The purpose of lactate threshold training is to keep your lactic acid production at a relatively controlled level, thus allowing you to maintain faster paces with no spikes in your blood lactate levels (Daniels, 2013).

The best way to improve your body’s use of lactate is to train AT your lactate threshold. Your training should be intense enough to increase your lactate level just before the point where it begins to spike. And yes, that’s a pretty specific point to hit, but where there’s a will, there’s a way!

Plus, there’s also actually a type of workout that was made specifically to help train your lactate threshold. So that’s pretty handy.

Tempo Workouts

Instead of always referring to these workouts as “lactate threshold training,” they’re often called “tempos” or “tempo runs.” Basically, they’re tempo runshorter, more moderately paced runs. As mentioned above, they make you run just fast enough to utilize the excess lactate at the same rate that your body produces it, which ensures that the lactate doesn’t build up in your bloodstream.

There are two types of recommended tempo training workouts: either do one continuous tempo, or break up the tempo into smaller intervals, or “cruise intervals” (Daniels, 2013). A continuous tempo can contribute to building confidence with your running, while cruise intervals break up a long tempo into smaller intervals and allow you to complete more volume. 

In order to improve your threshold pace, it’s best to perform tempos once a week (but there’s more specifics on that later). Below are a few suggestions for tempo variations based on your level of running experience.

Beginner: 

2-mile continuous tempo 

OR

3 x 1-mile tempo with 30 second jog break between each mile

Recreational: 

3-5-mile continuous tempo

OR

4 X 1.5-mile tempo with 30 sec jog between each rep

Advanced:

5-10-mile continuous tempo 

OR

4 x 3-mile tempo with 30 sec jog between each rep

Of course, while the type of tempos you do are up to you, they both come with their own potential benefits. For example, if you’re looking to push your lactate threshold, it’d be best to train with one long, continuous tempo without a break. But if you’re new to tempos, you’d benefit more if the tempo is broken up into smaller slices with a small amount of recovery. Additionally, if you want to increase the volume of your running, you can break up the tempo into more reps — that will ultimately add up to a larger distance total.

Keep in mind that tempo workouts can vary in intensity based on each individual runner, but these suggested workouts are a solid foundation to start with. But then that begs the question… how will you know if they’re actually helping you train your lactate threshold?

You ask the right questions, fellow runner.

H3: Determining the Right Pace for Tempo Runs

There are a few ways to identify if you are running at lactate threshold pace (and you’re welcome to use more than one to figure it out).

The most precise method is to run on a treadmill and have a specialist poke you with a needle to draw a bit of blood. A blood sample can allow the specialist to identify if your blood lactate is spiking as a result of your running intensity. (But let’s be real — getting pricked with a needle isn’t everyone’s cup of tea, and lab tests are expensive.)

A less invasive test is the 7 word talk test, which is nice and easy — while performing a tempo run, try to speak 7 words without gasping for air. Try to speak a 7-word phrase, like “I hold these truths to be self-evident.” (Okay, okay — we know that’s basically 8 words, but the hyphenated phrase technically counts as one word. Either way, it still works fine for the test.) If you find yourself unable to finish that phrase, or you end up huffing and puffing for air, then you’re already running too fast. There’s a direct correlation between your breathing and blood lactate levels, so increased or erratic breathing is a sign that your tempo is too intense. 

Running faster than tempo pace can actually be a whole different workout altogether, so if you were to maintain your workout at that intensity, you’d likely be struggling a whole lot by the end of it. Make sure you aren’t pushing yourself too hard, or else that un-fun burning feeling will creep up on you pretty quickly.

Lastly, you can experiment with calculating your ideal tempo pace using a tempo chart or a tempo calculator, or you can even try doing a time trial. Daniels created a pace chart that can predict your tempo pace — he created this chart based on his years of research and years of testing runners with a needle (those poor athletes). But hey, since he did all the poking already, you don’t need to poke yourself! 

If you’re not a fan of doing your own calculations, Runners World offers an online calculator that will identify your tempo pace for you. All you have to do is input your most recent PR and race distance, and it’ll calculate what your training pace is for tempos (as well as a variety of different workouts). Or, you can always run a 1-hour time trial to get your tempo pace. If you're a more advanced runner, a 10k can also predict your tempo pace. 

Once you’ve determined your tempo, the key to this training is to make sure that you maintain the proper pace and intensity. As long as you ensure consistency in your tempos, you’ll be well on your way to improving your body’s efficiency in clearing blood lactate!

When to Include Tempos in Your Workout Plans

Now comes the tricky part — figuring out when tempos are actually beneficial to your training can be a bit difficult to determine.

The quick answer is, it depends. 

There are several circumstances that contribute to whether or not a tempo should even be included in your training, not to mention when it should be implemented. You should speak with a running coach to help you best determine when to include tempos, the type of tempo workout, the pace, and distance. Ask yourself the following questions to help determine some of those factors:

  1. What is the race distance you want to accomplish?
  2. What is your level of experience with running?
  3. What is your current mileage?
  4. What are your race goals (i.e., do you want to run faster, or do you just want to finish a race)?
  5. What is your most recent PR?
  6. When is your next race? 
  7. Are you more of a fast-twitch or slow-twitch runner?

running coachThese questions are all helpful for you to know, that way you can better implement tempos into your training. For example, if your goal is to PR in an 800m race, then a tempo may not be a priority. However, if your goal is to run a faster marathon, tempos are essential and should be added sooner to your training plan. 

At the same time, you need to consider when to include recovery days, long runs, fartleks, intervals, repeats, etc. Developing a training plan can get extremely complicated, so it’s definitely best to consult with a running coach to ensure that you’re accounting for all the important facets of proper running training.

Key Takeaways

Ultimately, understanding your body’s lactic threshold can be super beneficial, especially as an endurance athlete. Although your body can respond to intense physical activity, it can’t predict how much or for how long it should generate additional energy for you, so it tends to overwork itself until fatigue sets in. 

Through lactate threshold training, you’ll have a much better handle on how hard you can push yourself without forcing your body into burnout. By improving your lactic threshold, you will be able to run that season PR or overall PR on your next long-distance race. 

References

Daniels, J. (2013). Daniels' running formula (3rd ed.). Champaign, IL: Human Kinetics.

Magness, Steve. The Science of Running: How to Find Your Limit and Train to Maximize Your Performance. Origin Press, 2014.


Pablo

Pablo Borceguin, DPT

Dr. Borceguin is the resident running expert of the Competitive EDGE team — in addition to his graduate degree from California State University, Fresno, he is well-versed in coaching multiple sports (e.g., high school cross country, track, and soccer) throughout San Jose and Fresno. Pablo is dedicated to using his experience as a coach, athlete, and healthcare professional to best educate his clients and other endurance athletes. He himself has competed in a number of sports, including cross country, track and field, multiple triathlons, wrestling, soccer, and tennis.