RPE & Heart Rate: Understanding Effort and Deciding What to Use

By Tyler Fox, Coach

Trail running involves changing terrain, shifting grades, varied footing, and unpredictable conditions. Because of that, measuring effort is more nuanced than simply looking at pace. Two common methods to attempt to quantify effort are RPE (Rate of Perceived Effort) and HR (Heart Rate). Both can be useful — and choosing the right method(s) for you is an important decision when thinking about your training!

Below explains what each tool is, how it works, and how to decide which fits your training best.

What Is RPE?

RPE (Rate of Perceived Exertion) is how hard the effort feels based on breathing, muscular tension, and overall sense of strain. For Type A personalities, it can feel like an overly subjective tool, but is often the most effective - It’s simple, intuitive, and responds instantly to terrain and fatigue.

The RPE Scale (1–10)

RPE 1–2 — Very Easy

Gentle movement, relaxed breathing
Warm-up, cool-down, recovery days

RPE 3 — Easy

Full conversation possible
“Cruisy” running; sustainable for a long time

RPE 4 — Steady

Breathing is deeper but still smooth
Talking in short phrases
Feels purposeful but not taxing

RPE 5 — Moderate

Noticeable effort
Talking becomes difficult
Requires light focus to maintain rhythm

RPE 6–7 — Hard / Tempo Range

Deep continuous breathing
Talking not possible
Controlled discomfort

RPE 8–9 — Very Hard

High breathing rate
Leg and lung fatigue prominent
Short, focused efforts

RPE 10 — Maximal

All-out
Unsustainable

Being perfectly tuned into where you fall on the scale isn’t easy and it takes practice! A good starting point is simply recording how hard a run felt (rating it 1-10 and even noting sections during the run that may have felt easier or harder) and describe accompanying feelings that you experienced. The scale you develop can be slightly different than what is listed above, but it’s important that you understand what it means and the efforts that you are describing with the values you’re using.

What Is Heart Rate Training?

Unlike RPE, heart rate ‘objectively’ measures your body’s physiological response to effort. The fact that it is measuring something physiological appears to make it a more accurate tool and more attractive to use as a result. However - and this is an opinion - HR is no more useful than RPE if implemented without an understanding of the nuance involved. In fact, if poorly understood, I often see it causing more harm than good.

Zones are often used to describe effort and represent different percentages of max HR or threshold HR. It is important to recognize that these zones are always changing in accordance to training load, areas of training focus, or simply a reflection of the fatigue you may be carrying from a previous workout or a response to a poor night of sleep.

Additionally, it is reasonably difficult to measure max HR and/or HR at the 2 commonly referenced thresholds (Aerobic Threshold/LT1 or Lactate Threshold/LT2). As you will see below, I wouldn’t suggest starting with trying to quantify these zones if you use an accurate HRM (heart rate monitor). And…if you do, I’d suggest professional testing/testing in a laboratory setting to do so and help guide that process.

General Heart Rate Zones (Approximate)

(Exact numbers vary person to person)

Zone 1 (Very Easy): ~60–70% max HR
Zone 2 (Easy Endurance): ~70–80% max HR
Zone 3 (Moderate / Tempo-ish): ~80–87% max HR
Zone 4 (Threshold): ~87–93% max HR
Zone 5 (High Intensity): >93% max HR

I’m not saying, heart rate isn’t useful. However, it is a more advanced tool and one that I often see poorly implemented. It can be heavily influenced by factors such as:

heat
altitude
hydration
stress or poor sleep
caffeine
technical terrain
acute training fatigue
Etc…

As a result, it takes a lot of practice and trial and error to know ‘exactly’ what HR may be telling you during any one training session.

RPE vs. HR — Which Should You Use?

If you’ve made it this far, you probably know my answer. It depends.

The recommendation I give for athletes is to first have a comfortable understanding of a RPE scale as it applies to you. This can be entirely based on the scale listed above or something that you have an easier time with. Again, there is no perfect way, but the process has to be standardized to your experience.

As hinted at above:

Step 1 — Start to develop an understanding of RPE.

At random moments during your runs, check in with yourself. How would you rate your experience? What number would you give it with regards to the RPE scale above?

Step 2 — Track RPE.

After your run - within the first 5-10 min - write down what you remember about it. How would you rank the effort overall? What sections stood out as harder or easier and what feelings accompanied those.

Step 3 — Reflect.

After a week/a month/a year/etc… look over your notes. Are you more comfortable with RPE? Does your historical tracking reflect an increased understanding? Can you pick out trends and see how they overlap with other possible stressors or life events? This step can give you the deeper understanding of what you are responding well to. You can even look over how the pace on a certain run at day 5 vs. day 55 changes and how RPE reflects either improved feelings of efficiency or stagnation. If you have a few weeks focusing on one type of training, you can see how that influences RPE. If you have periods of heavier or lighter training, that can be reflected in an interesting way!

Step 4 — Add HR?

If, over time, you want to ground your subjective experience in something more ‘objective’ like HR specifics, that’s a great step to take and a road map of how to do so is coming up. If you find you may be running too hard on easy days or want a more objective historical training log, HR can be a great tool! If you want another way to track stress across disciplines (run, bike, ski, etc…), it can also be really informative. However, HR is far from necessary and some of the best athletes out there have come a very long ways without it.

Using Both Together

If you think that you’d like to take that next step and look at adding in HR, here is an approach to do so without losing sight of RPE. Additionally, make sure that you are using an accurate monitor. Most external monitors (arm bands or chest straps) are ultimately most accurate. Wrist based options can be hit or miss and if going through the steps to add another tool, it’s best to spend the extra money to ensure it’s accurate.

Step 1 — Start every run using RPE.

Don’t look at HR for the first 10–15 minutes.

Step 2 — Once you’re warmed up, glance at HR at random intervals throughout.

This is just a starting point. You won’t have an intuitive sense of what HR correlates to a certain feeling/a certain RPE, but you’re gathering data points.

Step 3 — Glance at HR in different conditions.

Uphill/downhill, technical terrain, warm weather, etc… will all influence both RPE and HR. If you find yourself feeling like you’re working harder or easier, see how that is reflected in the HR feedback.

Step 4 — Start to guess and check.

Once you’ve developed an understanding of how different RPE values correlate to HR values, test yourself! This can be a pretty fun area to focus on during runs!

Step 5 — Reflect.

Continue to keep track of your notes after runs. Now, see how RPE and HR are related in the workout data. This is similar to points 2 and 3, but gives you a snapshot as the run as a whole and reinforces what you’ve learned during the runs themselves.

Step 6 — Test?

Some may disagree and note that this should be Step 1. However, similar to RPE, the best use of the systems intending on quantifying training are the ones that you understand. We can set up zones, but the underlying physiology of those zones is more complicated than any specific HR value will represent. Additionally, these ‘zones’ shift and being tied too closely to any one value can get in the way of effective training!

In Summary

Key takeaways:

Start with RPE. Learn how different effort levels feel, track those sensations, and look for patterns over time. A consistent RPE practice builds the foundation for all future intensity management.
Use HR cautiously and only once RPE feels intuitive. Heart rate can validate easy-day pacing, reveal fatigue trends, and provide a long-term training record—but only if you understand how external factors skew the numbers.
Combining RPE + HR works best when RPE remains the primary guide. Use HR as a loose reference point, not a rule to obey. Let HR confirm what your body is already telling you, rather than override it.
Zones aren’t fixed. They drift with training load, recovery, stress, and conditions. Treat them as approximations, not absolutes.
Testing is optional—not required. You can train effectively without formal lab testing, especially early on. Good self-awareness and consistent reflection often provide more actionable information.

RPE & Heart Rate: Understanding Effort and Deciding What to Use For Trail Running