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Training Zones, Heart Rate and RPE for Endurance Athletes

Spend a day on social media and you'll hear all kinds of opinions on training for endurance sports. Terms like training zones, heart rate, RPE (rate of perceived effort,) lactate threshold and more will commonly come up. What does it all mean?

First, I like to remind athletes that the intensity of your workout (run/bike/swim, etc.) determines its purpose. Let's generalize this in terms of running....

There is a traditional 5 zone model that gives runners an idea about how to relate intensity to purpose. We'll discuss these zones in detail today. For example, easy effort runs are lower in intensity and their purpose is to build and expand your aerobic base. In this intensity zone, your body is able to make many adaptations that will allow you to run for a long time without fatiguing. For example, positive changes in oxygen delivery and energy generation (via increases in capillary and mitochondrial density) happen in this zone. Generally, we call this easy effort zone "zone 2."

As we move up in intensity, metabolic changes happen to help support the increasing energy demands being placed on our bodies. As we move into zones 3, 4 and 5, we have to deal with the lactate shuttling system. Lactate is a molecule produced when we turn glucose into usable energy (aka ATP.) Lactate itself can be used as a fuel source. But if too much lactate builds up and exceeds this gentle balancing act of lactate production/lactate usage, we will begin to fatigue.

Instead of diving too deeply into the science, let's break down the 5 training zones and how heart rate and RPE can help us determine what zone we are in.

Zone 1: This is that extra easy effort zone where we are predominantly burning fat, very little lactate is being produced and you could sustain this activity all day if needed. Think of this zone as your easy recovery runs, brisk hikes or rucks or really easy cycling.

Zone 2: If you're an endurance athlete, this zone is your best friend. A large portion of your workouts should fall into this "aerobic base" training zone. This is your easy effort running that you could maintain for many hours with proper fueling and hydration. This is where you build that coveted aerobic base! Once you move out of zone 2, you will need to contend with the lactate shuttling system.

Zone 3: This zone is that "medium-hard" effort zone, also sometimes called the tempo zone. This effort zone can be maintained for 1-2 hours typically as long as you are fueling. The lactate system now becomes important at this effort level.

Zone 4: This zone is where we really kick up the effort. Talking aloud becomes harder to do in this zone. This zone could be maintained for 20-60 minutes depending on how conditioned an athlete is.

Zone 5: This is that high intensity effort zone where we will be pushing hard for speed work (short intervals, strides, etc.) This effort zone is not sustainable for too long due to the high demands for ATP and therefore the excess accumulation of lactate.

For recreational athletes who do not have access to laboratory testing, there are two main ways you can figure out which zone you are in: 1) heart rate data and 2) RPE (rate of perceived effort.)

Now, before we go any further, please note that heart rate can be a finicky thing. As a human being, heart rate can be affected by sleep, stress, diet, temperature, etc. So it's normal to have daily fluctuations. Also--that wrist watch you're wearing? The heart rate data from your watch isn't exactly the most accurate. But it does give us an approximation. These are good things to keep in mind!

Let's explore the two ways to set your training zones. First we'll deal with heart rate.

Heart Rate: for athletes who train with me, I find the best approach is to perform a field test to determine their Lactate Threshold Heart Rate. We then use this to set the zones based on that number.

To get an approximation of this heart rate, I employ a simple field test:

  • choose a day where you are not overly fatigued, you have slept well and are properly fueled

  • warm up for 10-15 minutes with some very easy effort running

  • you will now begin the field test: run as hard as you can for 30 minutes (preferably on flattish, non-technical terrain, and try to keep a substainable effort over the 30 minutes)---imagine you are racing a 5K

  • take the heart rate data from the last 20 minutes of your field test

  • the average heart rate from those 20 minutes is your Lactate Threshold Heart Rate (LTHR)

Now set your zones:

Zone 1/recovery zone: under 80% of your LTHR

Zone 2/aerobic zone: 80-88% of LTHR

Zone 3/tempo: 89-94% of LTHR

Zone 4/long intervals: 95-100% LTHR

Zone 5/short intervals: over LTHR

Not excited about heart rate data? Let's take a look at RPE (rate of perceived effort) instead!

RPE: rate of perceived effort--this is judging intensity by how it feels in your body, I like to use the "talk test" as you'll see below:

Zone 1/recovery zone: extra easy effort that you could perform all day long, you could sing and chat aloud all day long with no issues

Zone 2/aerobic zone: easy effort where you can still carry on a conversation aloud with ease (no getting breathless or having to use short phrases or extra pauses.)....also you could close your mouth here and breathe with ease just through your nose only

Zone 3/tempo:  here you may be able to still chat with your running buddy, but you may need some extra pauses and may notice that you're becoming a little more breathless at times....this is maintainable for 1-2 hours max

Zone 4/long intervals: in this zone it's becoming harder to talk aloud, you might be just sputtering short phrases and need extra time to catch your breath, you also probably can't maintain this for over an hour

Zone 5/short intervals: this is the hard work zone--talking aloud is very difficult and this effort is usually not maintainable for longer than a few minutes

After reading through all these methods, you mind find yourself asking...WHY? Why bother with training zones in the first place?

As an endurance athlete, you spend a lot of time training. And most of us have a day job and other responsibilities to tend to. By structuring your training with 75-80% of your runs easy and the remainder at higher intensity, you can be sure to reap all the benefits of each training intensity without becoming overly fatigued or spending too much time recovering. This is the evidence-backed way to optimize your training time!

The bottom line for determining effort zones on your own outside of a laboratory is this: heart rate and RPE can give us good approximations, but they aren't perfect in this setting.

If you get too bogged down in watch data and strava stats, I encourage you to take off your watch and run by time. In doing this, you can really start to get comfortable with RPE. No one knows your body better than you!

Once you've mastered RPE, try performing a field test to get to know your heart rate and where your zones lie.

At the end of the day, we are not chasing perfection or numbers. Instead, focus on getting to know your body and how RPE and heart rate reflect your intensity zones.

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