perceived exertion image of Cliff Pittman running rocky terrain

Perceived Exertion: How To Run And Train By Feel


By Cliff Pittman,
CTS Senior Coach &
CTS Coaching Development Director

Technology continues to profoundly impact training methods across the spectrum of endurance sports. However, a stubbornly low-tech assessment of effort and exercise intensity stands the test of time. Rating of perceived exertion (RPE) is about as simple as it gets: “On a scale of X to Y, where X is as easy as possible and Y is as hard as you can go, how hard is your current effort?” We’ll put numbers to the RPE scales later. First, it’s important to understand why RPE is more effective for trail and ultrarunners than heart rate.

The pros and cons of training by heart rate

Heart rate mirrors the body’s internal reactions to the rigors of physical exertion. Acutely, it provides a gauge of exercise intensity and aerobic fitness. Monitored over time, observations about heart rate response during training sessions and recovery periods can be a directional indicator of improving fitness, growing fatigue, overreaching, maladaptation to training, or even overtraining.

As CTS Coach Jason Koop describes in more detail here, many factors unrelated to exercise intensity can influence heart rate response. These include core temperature, caffeine and other stimulants, excitation/nervousness, hydration status, elevation, and fatigue. CTS Coach Jim Rutberg provides an example in this article, too, by asking, “So, what should your target heart rate be on a climb in a cold rainstorm at 10,000 feet above sea level, six hours into the Leadville 100? There’s no formula for that,… but you still know what an RPE of 7 out of 10 feels like.”

Limitations of Heart Rate

Sensor placement has created a new wrinkle in the use of heart rate during exercise, too. In the very beginning of heart rate monitoring (i.e., 1960s-1980s), sensors were stuck to the chest, clipped to an ear, or affixed to a wrist. The widely used heart rate chest strap became ubiquitous in the 1990s. The influx of wrist-mounted sensors in GPS watches and Apple watches, as well as finger-worn sensors like the Oura Ring, brought optical measurement of heart rate to the fore.

These devices rely on a technology known as photoplethysmography (PPG), which operates through LED lights, light absorption, and photodetection. Essentially, a wrist-based HR monitor measures changes in blood volume as light is absorbed by the vessels, rather than directly counting heartbeats as an electrocardiogram (ECG) or chest strap would. PPG is less accurate than ECG, and although the precision may not be critical during your average endurance run, those heart rate records are used for many of the “strain” and “recovery” scores within wearable devices and their associated apps.

Advantages of Rate of Perceived Exertion (RPE)

Rate of Perceived Exertion is a subjective assessment of an individual’s perception of how hard they are working during physical activity. Sometimes, the most intuitive solutions are the most effective.

While data enthusiasts may be fervently defending their metrics, the no-technology aspect of RPE often resonates strongly with trail runners. RPE is inherently subjective, and yet remarkably accurate when validated against physiological markers. Perhaps most important, RPE is accessible at all times and in all conditions because it doesn’t rely on equipment, batteries, or physical measurements.

Mastering RPE is a skill, and one I believe every runner should cultivate. However, it’s not something we can neatly chart in a file analysis or performance management graph. That’s part of the reason we still record heart rate and graded pace and other metrics, so we have data we can layer RPE on to create a fuller picture of the effort and workload performed.

Heart rate data serves a significant purpose in training. I often use it for analyzing individual workout files and long-term progress. However, I avoid prescribing training or race paces based on specific heart rate ranges for a predetermined duration, especially at higher intensities.

Rating of Perceived Exertion Scales

RPE was developed by Swedish psychologist and endurance sports researcher Gunnar Borg in the mid-20th century. Borg’s work on RPE was initially focused on quantifying the intensity of exercise and its physiological effects. He created the Borg Rating of Perceived Exertion (RPE) Scale as a tool for individuals to express their perception of effort during exercise.

The original Borg RPE Scale, introduced in the early 1960s, consisted of a numerical scale ranging from 6 to 20, with 6 representing no exertion at all and 20 signifying maximal exertion. In the 1980s, Borg revised the scale to range from 0 (no exertion) to 10 (maximal exertion) for greater simplicity and alignment with heart rate and physiological measures. This 6 to 20 scale is often referred to as the “original” RPE scale, while the 0 to 10 scale is commonly used today for its simplicity.

Validity and Advantages of RPE

The RPE scale gained prominence in sports science, exercise physiology, and coaching as a practical method for gauging exercise intensity. It has been extensively validated and is employed in various forms of physical training, from endurance sports like running and cycling to strength training and general fitness programs.

Fundamentally, RPE fosters a deeper understanding of one’s body, resulting in more effective training and pacing strategies. RPE is well-suited to the ever-changing nature of trail and ultrarunning, where factors like terrain and weather can shift rapidly, and durations can far exceed the point of aerobic decoupling. This adaptability empowers athletes to fine-tune their exertion in response to the conditions, preventing them from overexerting themselves in challenging situations.

Perceived exertion forges a direct connection between the mind and the body, encouraging athletes to tune into their bodies and have confidence in their instincts. This, in turn, can bolster self-assurance and alleviate anxiety during both training sessions and races. Furthermore, it necessitates no additional equipment or technology. It stands as a simple and pragmatic tool that can be applied in any setting, making it particularly well-suited for the world of trail and ultrarunning.

Practical application of RPE in ultramarathon training

At some level, you already know how to use RPE. If you have been running for any amount of time, you understand the connection between how you feel and how fast you’re going or how hard you’re working. The use RPE more effectively, let’s discuss how to incorporate it into your training. It’s a versatile tool that can empower you to understand your body better and make real-time adjustments in your training and races.

Step 1: Get to Know Your RPE Scale

Familiarize yourself with the RPE scale. It typically ranges from 0 (no exertion) to 10 (maximal exertion), or you can use the traditional 6 to 20 scale. Find what works best for you and ensure you can quickly relate your sensations to a specific point on the scale.

CTS RPE Scale of 1 to 10, with corresponding intensity, subjective measures, and training zones. Note RPE 1-3 would consist of activities such as sitting on the couch or walking.

Free Ultrarunning Training Assessment Quiz

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Recovery Run = Zone 1

Endurance Run = Zone 2

Steady State Run = Zone 3

Tempo Run = Zone 4

Running Intervals = Zone 5


perceived exertion scale

RPE scale used with specific CTS Running Workouts.


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Step 2: Practice During Training

Incorporate RPE into your training runs. As you run, periodically check in with yourself and assign an RPE value to your effort. Remember, RPE reflects how hard you perceive your body is working, so it’s inherently subjective. Use it to guide your training intensity based on how you feel that day. For example, if you planned a Zone 2 workout but your RPE suggests you’re pushing Zone 3 effort, consider easing off to maintain the desired intensity.

Step 3: Learn Your Body’s Signals

Over time, you’ll become more attuned to your body’s signals. You’ll recognize the difference between a sustainable, moderate effort and the signs of overexertion. Your RPE will become a trusted advisor, helping you adapt to varying conditions like challenging terrain, weather changes, or fatigue.

Step 4: Combine RPE with Heart Rate

While RPE is a valuable tool, it doesn’t mean you should abandon heart rate monitoring entirely. Rather, use it as a complementary method. In fact, pairing RPE with heart rate can provide you with a more comprehensive understanding of your performance, essentially calibrating your intuition with your physiology.

Step 5: Integrate RPE and HR for Optimal Training

Incorporate RPE and heart rate into your training strategically. For instance, during an easy long run, pay attention to your RPE to ensure you’re maintaining a comfortable pace. Post-workout, evaluate your heart rate to understand how your body is responding. This combination can help you strike the right balance between effort and physiological response.

In conclusion, while technology continues to advance, the simplicity of RPE remains a powerful and intuitive tool for trail and ultrarunners. It fosters a deeper connection between your mind and body, ultimately improving your training and racing strategies. So, next time you hit the trail, remember to listen to your body, trust your instincts, and keep RPE as a fundamental component of your training toolkit.

Adapted from content that appeared in Cliff Pittman’s column in Trailrunner Magazine.

Comments 6

  1. Yes, same question. If I do a RI session of 4x3mins + warm up + cool down; only 12 mins are at high intensity and the rest of the session is RR or ER. How do I rate the RPE of the session ?

    1. Post

      Thank you for your question. For a more complete description of aerobic decoupling, please see this article on heart rate training: The short answer is that aerobic decoupling occurs when the relationship between heart rate and power output (in cycling) changes during an exercise bout despite the pace or effort level remaining constant. This can reflect an increased internal cost to produce the external workload in, say, the third hour of a ride compared to the first. When an athlete experiences less aerobic decoupling it can be a sign their aerobic fitness is good; they can handle the steady workload well. Greater aerobic decoupling can indicate the athlete needs to improve aerobic conditioning before moving on to higher intensity work. – Jim Rutberg, CTS Coach

  2. Thanks for this, I especially like the summary table showing RPE, however, the challenge I have with this method is that some of my sessions vary in intensity, and so of course does the RPE.
    Is it best to take a perceived average score for the duration of your session ? 🤔🏃🏻‍♂️🏃‍♀️

    1. @Kate and @Steve R, when performing intervals, RPE should be applied to the intense bouts of the session (the work interval). If you want, you can use separate ratings for the recovery intervals.

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