Intensity Guidelines for 80/20 Running

by Matt Fitzgerald and David Warden

We recommend also reading Understanding Your 80/20 Run Plan and Understanding Your Structured Workout Plan

Your 80/20 Run plan employs a seven-zone intensity scale. Performing each workout and workout segment at the right intensity is at the heart of 80/20 training. This article provides all of the information you’ll need to determine your intensity zones so you can monitor your intensity during workouts and ensure you’re always in the right zone.

Your personal intensity zones can be automatically calculated based on the protocols described below at the Zone Calculator. Beginner athletes may find these tests difficult, so feel free to use perceived effort (explained in the second-to-last section) until you are comfortable doing the tests.

There are four ways to measure running intensity: pace, heart rate, power, and perceived effort. Each intensity type 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 less reliable when you’re running uphill or downhill.

Heart rate is helpful because it helps runners avoid the single most common training mistake: pushing too hard in runs that are supposed to be done at low intensity (Zones 1 and 2). But 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. HR for a given effort is also easily influenced by environmental factors such as temperature.

Power is the newest way to measure running intensity, and perhaps the most versatile. Using a running power meter, such as a Stryd, provides instant feedback on running output and is not compromised by terrain or temperature.

Perceived effort—or your subjective sense of how hard you are running—is important because it ultimately determines how fast you run in races. You may set and pursue time-based goals, but perceived effort has the final say in deciding whether you actually do maintain your goal pace or run faster or slower. However, perceived effort is poorly calibrated in many runners and relying on it exclusively carries some risk. In particular, most runners end up running at Zone X (in the gap between Zones 2 and 3) whenever they intend to run at low intensity if they go by feel. Whenever possible, use one of the more objective measures of intensity—pace, heart rate, or power—as your primary intensity metric.

Once you have chosen a method of monitoring intensity in your 80/20 training plan (and you may use more than one), you need establish personal intensity zones for that specific metric, which is done through lactate threshold testing.

Lactate Threshold

80/20 run plans use lactate threshold testing to determine training zones. Lactate threshold is defined as the exercise intensity at which lactate, an intermediate product of glucose metabolism, begins to accumulate in the blood. In practical terms, it’s the highest exercise intensity that can be sustained for up to 60 minutes. The most reliable field tests for use in identifying appropriate individual training intensities are those that pinpoint the lactate threshold (LT). Although monitoring the blood lactate concentration during exercise isn’t practical or easy, this isn’t a problem. The lactate threshold field tests detailed below are designed to reveal your pace, power, or heart rate at LT intensity, allowing you to use these more practical intensity metrics to regulate your effort in workouts.

LT represents the top end of Zone 3 in the 80/20 intensity scale and is the polestar for determining all other zones in the 80/20 Intensity Zone Calculator.

Run Pace 

Our training plans use a proprietary calculation for pace-based training zones. To determine your pace zones, visit the 80/20 Intensity Zone Calculator and enter a recent performance for one of the distances listed. The performance does not have to be a race, 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 may enter a known Threshold Pace (TP) from a previous testing protocol at the zone calculator.

A more accurate test is a 30-minute time trial (covering as much distance as possible in 30 minutes). This is a brutal, but precise method to establish your threshold pace. 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 30 minutes, being careful to avoid starting at a pace that’s too fast to sustain and thus slowing down involuntarily near the end. Your average pace for that 30 minutes is your threshold pace.

This test can be modified to just a 20 minute time trial, but using just 95% of your 20-minute speed in miles (or kilometers) per hour to determine your threshold pace. For example, if your average pace for 20 minutes was 8:45 per mile, first convert this result to decimal form, or 8.75 minutes per mile. Then, convert that value to miles (or kilometers) per hour. In this example, 8.75 minutes per mile converts to 6.86 miles per hour. Multiply 6.86 times 0.95 for an TP of value of 6.52 miles per hour. Convert 6.52 miles per hour back to minutes per mile, or 9.2 minutes per mile in this example, which is a TP of 9:12 per mile.

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.

When using the full 30-minute protocol, the need to perform separate tests for LTHR and TP is dispensed with entirely if you have a device that captures both heart rate and pace, as this enables you to establish LTHR and TP in the same field test.

Heart Rate 

The simplest way to determine your seven heart-rate based training zones is to back into them through pace. First, follow the guidelines under the Run Pace Section of this article and use the 80/20 Intensity Calculator to establish your run pace zones and 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 80/20 Intensity 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 30 minutes and hit the lap button on your heart rate monitor watch. 10 minutes into the time trial, press the lap button again. At the end of the 30-minute time-trial, hit the lap button one last time. Your LTHR is your average heart rate in beats per minute (BPM) for the final 20 minutes of the 30-minute test. The reason we use the last 20 minutes of the 30-minute test is that it often takes up to 10 minutes at lactate threshold effort for heart rate to “catch up” to your output.

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 of them.

Run Power

The protocol is similar finding your Run Pace. 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. Then, perform a 30-minute time trial. Your average power for that 30 minutes is your running threshold power, or rFTP.

Our colleague Jim Vance has developed a different protocol to find your rFTP. Additionally, the power meter manufacturer Stryd has developed a shorter test. This test should be performed on a running track, preferably a 400-meter track, and not on a treadmill. It can also be done with a GPS watch if you program the workout distance and duration in advance. Warm up for 15 minutes, then hit your lap button and run 1,200 meters (three laps) as fast as you can. Recover with a full 30-minute easy jog. Now run 2,400 meters (six laps) at maximal effort. Finally, cool down for 10 to 15 minutes. Find your average power for the 1,200- and 2,400-meter efforts and your total time for the 1,200- and 2,400-meter efforts. Your rFTP is calculated as follows:

(6-lap power x 6-lap time) – (3-lap power x 3-lap time) / (6-lap time – 3-lap time)

For example, if your average power was 350 watts for the 1,200-meter effort and 300 watts for the 2,400-meter effort, and your times were 5:20 (5.34 minutes) and 11:10 (11.17 seconds), respectively, the result would be:

(300 x 11.17) – (350 x 5.34) / (11.17 – 5.34) = 254 watts

The Vance or Stryd protocol can replace the Zone 3 section of a scheduled RT workout.

Regardless of which method you choose, enter the results into the Running Power section of the 80/20 Intensity Calculator to determine your zones.

Perceived Effort

While we don’t recommend that you use perceived effort as your primary intensity metric in training, it does have its place. Because perceived effort responds quickly to changes in intensity, it is a useful tool for establishing the right intensity at the start of each workout segment, before you have a chance to capture a split time and before your heart rate has had a chance to adjust to the change of intensity.

Note, however, that perceived effort increases the longer you go at any intensity, so it is only useful for establishing initial intensity. For example, at the end of a very long run at a moderate pace, your perceived effort level may be “14” even though you are still in Zone 2.

Use the guidelines in the following table to regulate your workout intensity by perceived effort. Note that these guidelines work in running as well as all in cross-training activities.


RPE Description 80/20 Zone


No exertion


Extremely light

Zone 1



Very light


Zone 2





Somewhat hard

Zone X



Hard Zone 3



Very hard

Zone Y and Zone 4


Zone 4


Extremely hard

Zone 5


Maximum exertion

Using Scheduled RT Workouts to Verify Zones

Because your fitness level and lactate threshold can change quickly, it’s important to keep your zones current throughout the training process by retesting your lactate threshold every few weeks. Repeating your chosen field test in every recovery week (recovery weeks fall ever third or fourth week in our 80/20 Run plans) is the theoretical ideal. As a practical matter, however, this is onerous for many athletes.

Fortunately, your 80/20 training plan includes frequent RT (Running Tempo) workouts that may serve as zone testing sessions. Most of these sessions feature Zone 3 effort that are less than 30 minutes in duration. Advanced athletes can replace these with the full 30- or alternative 20-minute time trials described above. Another option is to use the “backing in” method of verifying threshold pace or power. Because LTHR changes less than TP and rFTP over the course of a training plan, you can retest either of these variables in the context of RT workouts featuring Zone 3 efforts as short as 10 minutes by adjusting your effort until your heart rate levels off at your previously determined LTHR and observing the pace or wattage that corresponds to it.

Note that RT sessions occur less frequently in the L2 and L3 plans because 1) the high volume of these plans makes frequent high-intensity/high-duration testing risky, 2) we assume advanced athletes have a longer running history and are already confident in their lactate threshold, and 3) advanced athletes tend to experience smaller changes in lactate threshold than do beginner athletes. But if you ever feel you’re “outgrowing” your zones, feel free to insert one of the easier testing options into your next recovery week if it does not already contain an RT session.