For endurance athletes, there's never enough training time. And if you only have 12 hours a week to exercise, you want to make sure you get the most out of every workout.

The key is to train at a heart rate near or just below your aerobic threshold. As a hiker or mountaineer, you should be working out at this intensity about 70 to 80 percent of the time.

If you work out at a heart rate that's too high or too low, you'll be wasting valuable training time and may never reach your goals.

So how do you find out your aerobic threshold heart rate?

The best way is to measure your blood lactate levels during exercise.

Unfortunately, the most accurate lactate test is performed in a lab, so it isn't really practical for backpackers and mountaineers.Lactate tests are also expensive. If you repeat them to check your progress, the money is going to add up!

Fortunately, there is an absolutely free and easy aerobic threshold test that you can do right now.

It's called the talk test. It measures lactate levels indirectly based on changes in your breathing patterns. The talk test is super easy to administer, even for beginners.

Now, the talk test isn't the gold standard for aerobic fitness testing. So if you're really serious about dialing your aerobic threshold in, you might benefit from a more sophisticated lactate test (we'll discuss some options in a minute.)

But research suggests that the talk test is a useful tool for competitive athletes, recreational exercisers, and beginners.

So today, I'm going to show you how to use the talk test to easily estimate your aerobic threshold heart rate and your optimal heart rate training zone.

If you want to dive right in, skip down to the section "Aerobic Threshold Testing Guidelines." But if you want to understand some of the science behind blood lactate levels, heart rate, and endurance training, check out the next few sections.

What Is Blood Lactate, and Why Should You Care About It?

Lactate is a substance created by your muscles to fuel anaerobic (sugar-burning) metabolism. It's actually a clever way for them to recycle the metabolic waste products that build up during exercise.

Most lactate gets burned by your muscles as fuel. But a small percentage of it leaks into your blood, where it can be detected by a blood test.

Blood lactate levels increase with exercise intensity, but the relationship isn't linear. It's more like a curve, and there are two points where the curve steepens.As it turns out, these two "thresholds" correspond with changes in your breathing patterns. Both are very important markers that can help you exercise at the right level.

Aerobic threshold (also known as ventilatory threshold 1, VT1)

This is the exercise intensity where blood lactate levels rise above baseline (resting) levels. When you reach this intensity/HR, you will notice your breathing speeding up. Knowing the heart rate that corresponds to your aerobic threshold can make or break your endurance training.

When you're exercising above your aerobic threshold, your muscles aren't getting enough oxygen to run on aerobic metabolism alone. So they also start to burn some glucose (anaerobic metabolism).

Anaerobic metabolism allows you to exercise at higher intensities. But it also creates nasty byproducts that make your muscles fatigue and burn.

When you're out hiking and climbing, you generally want to stay in your aerobic zone (below your aerobic threshold) most of the time to prevent fatigue.

Endurance athletes should spend most of their time training at a heart rate 0–10 beats below their aerobic threshold. (This heart rate range is also known as Zone 1.)

By training in Zone 1 70–80 percent of their time, you'll improve your body's ability to deliver oxygen to the working muscles through:

• Improved pumping power of your heart

• Greater capillary density around your muscles

• More mitochondria (energy producing structures) in your muscle cells

• Increased production of certain "aerobic" enzymes

This will actually raise your aerobic threshold over time.

It's important to note that training below your aerobic threshold isn't necessarily slow, although it will be for many people. Well-conditioned athletes can have aerobic thresholds that are relatively high — up to 85 percent of maximum heart rate.

Anaerobic threshold (lactate threshold, VT2)

As exercise intensity and heart rate rise above the aerobic threshold, your blood lactate levels rise.

Acid is a byproduct of lactate creation. This also builds up in your blood causing your blood pH to rise.

Fortunately, your blood contains substances that can combine with the acid to neutralize it (or "buffer" it). This buffering process creates excess carbon dioxide which must be exhaled through your lungs. This is why you breathe faster when you're working above your aerobic threshold.

These buffers also react with lactate to create new substances that can be used by the body as fuel.

If exercise intensity/heart rate continues to increase, your body will start creating so much lactate and acid that your body can't buffer them fast enough. Above this point, your blood lactate levels will increase exponentially with intensity.

This threshold (and the heart rate that corresponds to it) is known as the anaerobic threshold. Other names you might hear include lactate threshold, onset of blood lactate accumulation, or second ventilatory threshold (VT2). They're all a little different but correspond to about the same exercise intensity and HR.

As you exercise above your anaerobic threshold, your body fatigues due to acid buildup in the muscles and blood. Depending on your fitness level, you may be able to sustain this pace for 30 to 45 minutes, but probably not much longer.

Training at a heart rate above your anaerobic threshold can improve your overall fitness and give you a burst of power when you need it (for example, to power up a difficult obstacle or run from a serac fall). But as a hiker, it's probably not going to be the major focus of your training.

In summary

• Blood lactate levels rise with exercise intensity and heart rate

• The aerobic threshold is the intensity/HR where blood lactate levels begin to rise

• As blood lactate levels rise, breathing speeds up

• Hikers, backpackers, and mountaineers should mostly be training below their aerobic thresholds (Zone 1)

Why Do Different People Have Different Aerobic Thresholds?

High-Altitude Mountaineer Steve House and I are both in our 40s, but exercising at his aerobic threshold would make me collapse in under an hour. Why is his aerobic threshold so much higher than mine?A few reasons:

• He's in better shape. Steve's training volume (hours per week) is probably at least three times greater than mine. He's also been training longer, more consistently, and more effectively. Therefore, both his aerobic and anaerobic thresholds are higher.

• He may also have a genetic advantage that allows him to adapt faster than average to aerobic exercise. However, genetic factors are far less important than quality and consistency of training.

• As we discuss in a minute, maximum heart rate varies considerably among people of the same age. So my max heart rate may actually be 12 to 18 beats lower than Steve's, which means my aerobic threshold and anaerobic threshold will also tend to be lower.

My point: If you take the talk test and your aerobic threshold seems really low, don't despair. There's more to fitness than your lactate profile.

Two people with the same aerobic threshold can vary quite a bit in performance based on factors like muscular strength, skill, body mechanics, nutrition, and psychology.

It's also important to note that lactate profiles change with training. If I train well for a few months, my aerobic threshold will get closer to Steve's. This is why it's so important to repeat the talk test every few weeks during your training season. (More on that in a minute.)

What Is Lactate Testing?

Lactate tests measure your blood lactate levels, either directly (using a drop of your blood) or indirectly (looking at exhaled carbon dioxide levels or changes in your breathing).

The goal of lactate test is to create a lactate performance curve. This is a graph that plots your blood lactate level against your heart rate. Here's the example from above:

A lactate test is the best way to pinpoint your aerobic and anaerobic thresholds and the corresponding heart rates so you can train at the best heart rate to get results.

But can't I just use heart rate formulas?

Some books, coaches, and websites tell you that your heart rate Zone 1 (below your aerobic threshold) is about 60 to 75 percent of your maximum heart rate. They also give you a formula to calculate your maximum heart rate (220 - Age is a popular one). And then you can go from there, right?

Well, no. This approach is easy for beginners to understand. And it's better than nothing. But not much better.

The problem is, maximum heart varies greatly between people of the same age.

If you're into math, consider that the 220 - Age formula has a standard deviation of 12.

I'm 42, so my predicted maximum heart rate would be about 178. But the majority of 42 year-olds actually fall somewhere between 166 and 190, which is a huge range! (And about one in three is actually even further outside that range.)

Also, the "heart rate zone" is based on the average population, not athletes (which you are). If you are really fit, your aerobic zone may actually be up to 85 percent of your maximum HR. If that's the case, working out at 60 percent of your maximum HR won't produce the results you want.

What Kind of Lactate Tests Are Available?

While this post is going to focus on the talk test, you may want to try a more precise lactate test at some point. Here's a run down on your options:

Gas Exchange Test

This lab test is the most accurate lactate test available. Usually this means visiting the exercise physiology department of a research university. In some areas, you can also test at a commercial fitness lab.

To perform this test, you'll need to exercise while wearing a mask that captures your exhaled gases. The tester will put your through a graded exercise test that gradually increases your heart rate. The amount of carbon dioxide you exhale is an accurate marker of your blood lactate levels.

A few caveats: Most athletes use this test to find their anaerobic threshold (not aerobic), so you might have to do some explaining to get the measurements you want. Also, keep in mind that your aerobic threshold may be slightly different on trail than when you're jogging on a treadmill in the lab.

Near Infrared Spectroscopy (NIRS)

Consumer devices are now available that can plot your lactate curve based on HR and oxygen saturation levels in your muscles. Simply strap the monitor band to your thigh or calf, do your normal workout, and the software does the rest. The downside: most NIRS technology is still cost-prohibitive for amateur athletes. (For example, the Moxy Monitor starts at $800 before add-ons and software.)

Handheld Lactate Analyzer

These devices work a bit like the glucose monitors used by diabetics. Just establish a steady state heart rate, prick your finger, squeeze the blood onto a testing strip, and stick it in the machine for a reading. Boom, there's a data point for your lactate v. heart rate graph. Repeat the test at different heart rates to construct your lactate curve.

You can buy your own lactate analyzer for $280 to $350, plus the cost of lancets and strips. This is a good option if you're going to be doing serious training and want to monitor your progress over time. As you can imagine, it also helps to have a partner who can assist with the pricking and testing while you focus on your workout.

Some sports camps and clubs offer this test to participants.

Heart Rate Monitor

Garmin, Wahoo Fitness, and other heart rate monitor manufacturers have developed HR algorithms that can be used (in theory) to estimate your aerobic and anaerobic thresholds. In the case of Wahoo Fitness, the phone app will actually put your through a short field test and calculate your "Burn" and "Burst" zones, which I assume are aerobic and anaerobic training zones.

Also, the company doesn't post information on how the algorithm works. So there's no way for me as a trainer to evaluate its validity.

It's totally possible that these algorithms work better for some people than others, so if your device has this feature, go ahead and give it a try. But treat the results with a grain of salt until you've verified them against other forms of testing (like the talk test below).

Field Tests

While not as accurate as high tech devices and lab tests, field tests can often help you pinpoint your aerobic and anaerobic thresholds within a few heartbeats. Major advantages of these tests include costs (free!), ease of administration, and the fact that you can repeat them often to check your progress.

There are tons of field tests out there for estimating your anaerobic threshold. Here's a video I made describing the 20-minute running test:

Now of course, as hikers, backpackers, and mountaineers who do a lot of Zone 1 training, we're most interested in measuring our aerobic threshold. So as I mentioned above, I recommend a simple talk test for estimating your aerobic threshold heart rate.

So now that we've talked about the science behind it, let's look at a talk test protocol you can do in the gym or even while jogging outside.

Using the Talk Test to Find Your Aerobic Threshold

The talk test takes about 15 minutes to administer. To do it accurately, you'll need a heart rate monitor. Here are some guidelines to follow before testing:

• This test is generally safe for most people. But as with all exercise programs, check with your doctor before exercising if you have any chronic conditions like heart disease, asthma, or diabetes.

• Be well rested. The test will be most accurate on the day after a rest day or easy training day. Perform the test before your regular workout.

• Test at the same time of day you normally work out. (Your heart rate changes throughout the day.)

• If you have time, do a separate test for each of your training disciplines (running, hiking, cycling). Your aerobic threshold may be a little different for each activity.

• Perform the test at least two hours after your last meal, and avoid caffeine on test day.

• If possible, test on a flat surface like a running track. A treadmill also works.

• If you'll be testing outside, try to avoid hot or windy weather that could stress your body and raise your heart rate.

Got it? When you're ready to go, here are the steps to follow to execute the talk test.

• Start with an easy 5–10 minute warmup. Keep your heart rate below 120.

• When you're ready to begin the test, pick up the intensity a bit so that your heart rate rises to about 120.

• Once your heart rate has been steady for 2-3 minutes, start talking! Recite the pledge of allegiance, the ABCs, or a scene from your favorite movie. If you run out of words, just repeat. The goal is to keep talking for 30-40 seconds. NOTE: Yes, this looks hilarious if you're doing it in the middle of a public park. If you feel self-conscious, bring a friend to talk to. Or pretend you're on your phone.

• If you're working below your aerobic threshold, you should have no problem talking for 30 seconds. It's fine to take a deep breath between phrases. But you shouldn't feel oxygen starved, gaspy, or like you want to stop talking.

• Another good sign that you've reached your aerobic threshold: nose breathing becomes snorty and difficult to sustain.

• Repeat the above steps increasing your heart rate by 3-5 each stage until talking becomes difficult.

• Once you hit your aerobic threshold, slow down a bit and find the highest heart rate where you can talk and nose breathe easily, even when sustaining that heart rate for 10 minutes or more. Your heart rate at this pace is your aerobic threshold heart rate and the top of your training Zone 1.

Sound easy? Well, it is for some people.

If you're having a hard time finding your aerobic threshold:

• Be patient. It may take some practice to get it right!

• Make sure you're looking for the right breathing patterns. Start running hard and note how your breathing changes as your heart rate rises. See how it's starts by deepening, then speeds up, then gets shallower? We're trying to pinpoint the heart rate at which it starts to speed up (making talking difficult).

• Increase your heart rate in smaller increments (3 beats instead of 5).

• Make sure you're achieving a steady-state heart rate (no more than +/- 1 variance over a minute) before you start talking.

• If you haven't found your aerobic threshold within 20–30 minutes, stop the test and try again on a different day.

• Try testing on a treadmill. Sometimes it's easier to achieve a steady-state heart rate in controlled conditions.

Aerobic Threshold Test FAQs

How do I use my aerobic threshold to determine my training pace?

Endurance athletes should spend 80–90 percent of their training time in heart rate zone 1. This corresponds to your aerobic threshold heart rate and the 10 beats below it.

Does the talk test work for everyone?

Nope. About 10 percent of the population has a hard time achieving a steady-state heart rate. Certain health conditions and medications can also change your breathing and heart rate responses.

If you fall into any of these categories, you may need to use a different strategy such as Ratings of Perceived Exertion (RPE) to monitor your workout intensity. (The RPE is also great for those workouts when you don't have your heart rate monitor handy!)

I'm really struggling with this. Is there any other way to estimate my aerobic threshold?

Yup. Try the MAF method. Subtract your age from 180 to estimate your aerobic threshold. Repeat the talk test, and watch what your breathing does as you approach this number. When I tried this after a month off from cardio, it was correct within a couple of beats.

Caveat: This method is better for beginners and less accurate for athletes who have been training for awhile.

Can you recommend a good heart rate monitor?

You can read my full Wahoo TICKR review here.

What's a good aerobic threshold?

There's really no such thing. Aerobic threshold depends on many factors, including your age, physiology, and genetics, so there's no point in comparing yourself to others. There's only "good for you." With training, you'll see your aerobic threshold rise over time, which is a great feeling.

Have you ever had a lactate test? (Like a real one?)

Nope. But I'm thinking about it! I would love to see how my talk test aligns with actual science. If it happens, I'll definitely post to let you know how it goes.

Conclusion (Simple, No Science)

In order to make the most of your limited endurance training hours, you need to train at the right intensity. As an endurance athlete, most of your training should be in the super-efficient "aerobic zone."

No fancy heart rate formula can calculate your aerobic zone accurately. It's better to look at physiological changes that occur as exercise intensity increases. Specifically, you need to find your aerobic threshold — the intensity where lactate produced in your muscles starts to enter your bloodstream.

You can use many fancy tests to find your aerobic threshold, including blood lactate tests. But a simple talk test will provide a good estimate for most people. Find the heart rate at which your breathing speeds up and talking becomes difficult. It's really that simple.

Once you know your aerobic threshold heart rate, work out within 10 beats below it to maximize your aerobic fitness. This intensity is called training zone 1. You should spend 80 to 90 percent of your training time here.

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So there you have it. A big fat nerd fest on aerobic thresholds and blood lactate tests ...

Which all adds up to this: work out at a pace where you can still talk on your phone.

Did you give the aerobic threshold test a try? How did it go? Comment below to share your experiences and advice.

Originally published Sept. 13, 2018.