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We recommend also reading Understanding Your Endurance Lab Run Plan and Understanding Your TrainingPeaks Structured Workout Plan


Your Endurance Lab Run Plan employs a seven-zone intensity scale. Performing each workout and workout segment at the right intensity is at the heart of balanced training. This article provides all of the information you’ll need to determine your personal threshold and intensity zones so you can monitor your intensity during workouts and ensure you’re always in the right zone.


Determining your intensity zones is a three-step process. Step one is to choose a preferred way of measuring intensity. Step two is to perform a field test to assess your threshold. Step three is to calculate your zones from that threshold with the help of our zone calculators. Additionally, you can always book a session at one of our Certified Labs and get the most accurate zones calculated.



There are three ways to measure running intensity: pace, heart rate, and power. The testing protocols for all three metrics are listed below. Each metric has advantages and disadvantages relative to the others:


Pace is useful because it’s a performance-relevant variable. You race on the clock, so why not also train by the clock? However, pace becomes unreliable when you’re running uphill or downhill.


Heart rate has the advantage of reflecting physiological intensity, or how hard your body is working, unlike pace and power. However, heart rate is not a reliable way to monitor intensity during short efforts at high intensity because heart rate lags behind abrupt changes in pace. Heart rate is also influenced by environmental and other factors, including temperature and hydration status, that can distort its relationship to actual exercise intensity.


Power is the most versatile way to monitor running intensity. As a pure measure of your work output, power is the same in all conditions, requiring fewer conditional adjustments than pace and heart rate. Less familiar than the other intensity metrics, though, power-based training takes some getting used to.


Power is an output, pace is an outcome, and heart rate is an indicator. To help you further distinguish the respective advantages of each intensity type, let’s use an automobile as an example. Horsepower (power) is the output and represents actual work performed regardless of terrain, grade, or environmental factors. Your speedometer (pace) indicates the speed or outcome. Your engine temperature (heart rate) represents how the car is responding to the output and environment. During a hilly ascent, the output (power) might be high, but the outcome (speed) might be low. On a hot day, the engine temperature (heart rate) might be very high even when stopped at a light with almost no output and zero outcome. For this reason, power is considered superior to pace, and pace is superior to heart rate to measure intensity. There are some exceptions, such as hills, where HR can be superior to Pace to measure intensity. The recommended best practice is to use Power or Pace as your primary measure, with HR as a secondary measure.


Once you have chosen a method of monitoring intensity in your Endurance Lab Run Plan (and you may use more than one), you need to establish a personal threshold for that specific metric through field testing. The threshold is unique to each runner and evolves with changes in fitness. Several different field tests have been scientifically vetted and shown to accurately measure your current run threshold.


The most reliable way to determine your pace threshold is to enter a recent race result for the 5K, 10K, half marathon, or marathon distance into the Endurance Lab Zone Calculator. The performance does not have to be from an official race—a virtual or solo race will do—but it should reflect your current maximum capability for a given distance, whether it comes from competition or training or is simply an estimate of how fast you could run a given distance today.


Alternatively, you can perform a 20-minute time trial (covering as much distance as possible in 20 minutes) to determine your Threshold Pace (TP) and enter this number into the appropriate field of the Endurance Lab Zone Calculator. Begin with a warm-up that consists of 15 minutes of easy jogging that ends with a few 15-second surges at the pace you intend to run for the time trial. Next, run as far as you can in 20 minutes, being careful to avoid starting at a pace that’s too fast to sustain and thus slowing down involuntarily near the end.


If you already know your lactate threshold heart rate (LTHR), you can use it to find your TP with an even shorter field test. After warming up, play with your pace until your heart rate settles in at your previously established LTHR for 10 minutes. Your pace at this heart rate is close to your TP.


The simplest way to determine your heart rate threshold is to back into them through pace. First, follow the guidelines under the Pacing Testing section of this article to establish your Threshold Pace (TP).


The next step is to determine your Lactate Threshold Heart Rate (LTHR) from your TP. To do this, warm up with 10 minutes of easy jogging and then accelerate to your TP on a smooth, flat path or road. Wait for your heart rate to stop increasing and plateau. The number you see after it levels off is your LTHR. Now go to the Run and Cycling Heart Rate section of the Endurance Lab Zone Calculator and enter your Lactate Threshold Heart Rate. Your seven heart rate training zones will be calculated automatically.


If you have not yet established your TP, you can find your LTHR independently through a time trial. Begin with a warm-up that consists of 15 minutes of easy jogging with a few 15-second surges at the pace you intend to run for the time trial. Next, increase your effort to the highest level you feel you can sustain for 20 minutes and hit the lap button on your heart rate monitor watch. Five minutes into the test, hit your lap button again. Fifteen minutes later, at the end of the 20-minute time trial, hit the lap button again or end the time trial. Your LTHR is your peak 15-minute average within that 20-minute test (the average heart rate in beats per minute (BPM) of the final 15 minutes of the 20-minute test).


Note that Lactate Threshold Heart Rate is slightly different in running than it is in other aerobic activities, so if you choose to cross-train, you’ll need to do separate tests in each activity.


Also note that heart rate is significantly influenced by factors such as temperature, humidity, sleep, stress, time of day, and even when you last ate. Therefore, your Lactate Threshold Heart Rate test result is specific to the environment and conditions in which you test. For example, an LTHR test indoors in February in the morning will not be the same as an LTHR test in July outdoors in the afternoon. Perform your LTHR in the environment that most accurately represents where you will do the bulk of your training.


For various reasons, most athletes find that their threshold is 5-10 bpm lower indoors than outdoors. For this reason, it may be practical to maintain separate indoor and outdoor HR zones. Or simply adjust your zones appropriately when moving between outdoor and indoor environments.


The most straightforward field test to find threshold power is a 20-minute time trial. Begin with a warm-up that consists of 15 minutes of easy jogging with a few 15-second surges at the pace you intend to run for the time trial. Next, run as far as you can in 20 minutes, being careful to avoid starting at a pace that’s too fast to sustain and thus slowing down involuntarily near the end. Your running threshold power, or rFTP, is equal to 95 percent of your average power over the full 20-minute time trial, which can be entered into the 80/20 Zone Calculator.

The leading brand of run power meters, Stryd, offers a different way to establish power zones. Stryd power meters automatically estimate a variable called critical power (CP) for individual runners through their use in the normal training process. For Endurance Lab structured workouts to sync to appear in the Stryd platform and apps with the same power targets that you find in TrainingPeaks, it is recommended that you disable Stryd’s Auto-Calculated Critical Power and manually set the Stryd CP to match your rFTP as it is defined above. 


If you already know your lactate threshold heart rate (LTHR), you can use it to find your rFTP with a short field test. After warming up, play with your power until your heart rate settles in at your previously established LTHR for 10 minutes. Your power at this heart rate is close to your rFTP.


Once you have a result from your chosen field test, go to the pace calculator and enter it in the appropriate field. If you wish to have your zones automatically sent to your Endurance Lab workouts on TrainingPeaks, follow the steps outlined in the document Understanding Your Structured Workout Plan.


As your fitness level changes, you will need to adjust your zones to keep them current. Races are natural opportunities to update your pace zones. For example, if you complete a 5K race during Week 6 of a 12-week 10K training plan, use your 5K time to update your pace zones.


Many athletes like to update their zones on a regular schedule. If you wish to do so, choose a preferred testing method and repeat it during every second recovery week beginning with the first recovery week of your plan. Note that recovery weeks fall every third week in all of our run plans. If you elect to perform scheduled testing, you will test in Week 3, Week 9, Week 15, etc. Your zone tests will be least disruptive to the overall training process if you do them in place of the most challenging workout of the relevant week that features efforts in Zone 3 or higher. For example, the most challenging workout featuring efforts in Zone 3 or higher in Week 9 of our LV 1 Half-Marathon Plan is a Hill Repetitions Run. This would be the best run to replace with a test.


Also note that if you are an intermediate or advanced-level runner and you use heart rate as your primary intensity metric, you probably don’t need to update your zones very often. This is because LTHR doesn’t change a lot with changes in fitness once you’re past the beginner (or starting-over) phase. What you will find as you gain fitness is that you run faster and faster at the same heart rates. Indeed, one simple way to update your pace or power zones is to do a test where you run at your current known LTHR and identify the corresponding pace/power, then plug this number into the appropriate calculator. For example, if you know that your LTHR is consistently stable at 160 BPM but you notice that you’re running faster at any given HR lately, do a run where you lock into a heart rate of 160 BPM and note the corresponding pace/power. Say your pace is 5:30/Km at this HR. This, then, is your approximate Threshold Pace. It’s best to do this particular test within the context of a scheduled run that targets Zone 4.

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