Recently I had a patient come to me during his appointment very concerned. He explained to me that he was a member of one of those HIIT heart-rate based fitness class gyms. He went on to say that he was concerned about his health because he could never get his heart rate as high as some of the other members of the class, despite the fact that he was working at a very high perceived exertion. In his words, he could never get his heart rate in to the “red-zone” — the highest training zone. Because of this, he felt his performances in the gym were never good enough. After significant discussion and a little bit of examination, it became clear that his health was not the reason for his heart rate not getting in to the “red zone” — the reason was that his heart rate zones were set inaccurately to begin with.

Like many heart rate based exercise programs, the heart rate zones for this individual were set based on an age-based heart rate formula. This method estimates maximum heart rate by taking 220 and subtracting your age. From this, theoretical heart rate training zones can be estimated. This method for estimating heart rate zones can give you a reasonable ballpark of where your heart rate zones are, but it can also be off by up to 40 beats per minute.

In the case of my patient above, I can only imagine how hard this patient was working in his class, pushing himself beyond his limits, gasping for air, only to be disappointed that the gentlemen next to him working at only a brisk pace was putting up “better numbers” on the board. I use this example, because it illustrates clearly how inaccurately measuring intensity can set-up athletes or individuals training their bodies for failure.

Of course there are many ways to gauge intensity during training. However, when it comes to cardiovascular training, heart rate zone based training is one of the most effective and accessible ways to guide intensity — this includes optimizing individual workout performance and preventing overtraining. Using inaccurate zones can lead to inefficient workouts, overtraining, poor adaptation over workout blocks, and increased injury risk.

Why Heart Rate Zones Matter

Heart rate zones help athletes structure their training by ensuring each activity within a session has a specific physiological purpose. For example, lets say yesterday you did a hard run workout and today’s workout is supposed to be much lower stress, or easier. Great! Well, how do you know your doing today’s workout easier? You could guess based on perceived exertion, and sometimes that has value, however sometimes outside factors can affect how you feel. The answer lies in keeping your heart rate in a certain range. If you go above the zone, you are working too hard, if you go below the zone, you aren’t working hard enough. Get it?

Each zone correlates to what is happening inside of the body. Zone 1 and 2 are fully aerobic. This is considered low intensity and is associated with activity that is lower stress on the body. Zone 5, is fully anaerobic. This correlates with a heart rate that is very high and associated with activity that is very stressful. Zones 3/4 are somewhere in the middle –moderate intensity — not fully aerobic, so lactic acid is starting to accumulate in the body. In other words, heart rate zones tell us what is happening inside of our bodies and how quickly fatigue and stress are accumulating in the body.

Training too hard too often leads to burnout, while training too easy may not elicit the adaptations needed for peak performance. Understanding your appropriate heart rate zones allows you to guide each workout or even each segment within a workout, optimizing time spent in aerobic zones, at balanced threshold pace, and higher anaerobic intensities.

The Problem With Age-Based Formulas

Many athletes rely on the traditional 220-minus-age formula to determine their max heart rate and subsequent zones. However, this method is often inaccurate because heart rate variability is highly individual. Factors such as genetics, fitness level, medications, and even daily stress impact an athlete’s actual heart rate response.

Hopefully we learned from my patient in the example above, inaccurate heart rate zones leads to inappropriate training. At the very least this will be frustrating. On the far end however it can lead to injury, burnout, and failure.

The 30-Minute Field Test: A More Personalized Approach

In 2018 I completed my first triathlon — an Olympic distance triathlon in south Florida. My performance was nothing to write home about, but I knew immediately I had found a sport and passion that I was hooked on. After that race I knew I had much to learn about the sport. After scouring the internet for resources I stumbled on The Triathletes Training Bible by Joe Friel. I still recommend this book to anyone looking to learn more about endurance and triathlon.

In his book, Joe Friel, a well-respected endurance coach, developed a simple yet effective way to determine lactate threshold heart rate (LTHR), the key metric for setting individualized heart rate zones. The test is straightforward and takes 30 minutes:

1. Warm-up: 15-20 minutes of easy running or cycling.
2. Time Trial Effort: Perform a 30-minute all-out, solo effort as if racing. You should go hard the entire 30 minutes.
3. Heart Rate Measurement: Using some type of watch or fitness tracker, record your average heart rate for the final 20 minutes of the effort—this is your estimated LTHR (Lactate Threshold Heart Rate).
4. Establish Zones: Using Friel’s guidelines, you can categorize heart rate zones based on percentages of your LTHR.

Why I Recommend This Method

• Individualized: Unlike generalized formulas, the 30-minute test reflects your current fitness level and adapts over time.
• Accessible: No need for a lab test; it can be done with just a heart rate monitor and a stopwatch.
• Reliable: It provides a practical way to measure and adjust training intensity based on real-world performance.

Implementing Your Heart Rate Zones

Once you have your LTHR, you can break it into zones using Friel’s framework:

• Zone 1 (Recovery): <85% LTHR
• Zone 2 (Endurance): 85-89% LTHR
• Zone 3 (Tempo): 90-94% LTHR
• Zone 4 (Threshold): 95-99% LTHR
• Zone 5 (VO2 Max): >100% LTHR

With these zones in place, you can structure your workouts with precision, ensuring that easy days remain easy and hard days truly challenge your system.

Final Thoughts

Training smarter—not just harder—leads to better endurance gains, reduced injury risk, and improved race-day performance. By using Friel’s simple 30-minute test, athletes can establish heart rate zones that reflect their true capabilities, allowing them to maximize training efficiency accurately. Whether you’re training for your first Ironman or simply looking to improve your endurance, this method is one of the best tools to optimize performance.

Now that you know how to find your heart rate zones, stay tuned in the future as we learn how to use these zones!