Whether runners should use rate of perceived exertion (RPE) or heart rate monitors is the question. At best, this is a heavily debated topic of which approach is best, with an incredible amount of nuance within each modality. As an athlete and coach, my experiences have ranged from receiving many questions around this topic, to meeting others with strong opinions one way or another. I come in with my own biases, but hopefully this article, although not comprehensive by any means, will shine a light on the pros and cons of each tool and how/when to integrate them both simultaneously.
What is Rate of Perceived Exertion (RPE)?
RPE is a subjective measure of the perceived intensity level when doing a workout. RPE was created by Dr. Gunnar Borg, a Swedish psychologist, who created 2 different RPE scales. For the sake of this article, we’ll be using the Modified Borg CR Scale 1-10 RPE rating.
Referring to the Modified Borg CR Scale 0-10, this is how I typically outline workouts according to RPE:
- 0 – at rest
- 1-3 (walking) very easy to breathe
- 4 (recovery run) easy to breathe
- 5-6 (endurance run) conversational pace run; breathing is not labored
- 7 (steady state run) labored breathing; able to speak a couple sentences
- 8-9 (tempo run) elevated deep & labored breathing; able to say several words
- 10 (intervals at VO2 max) maximum intensity; short and rapid breathing; barely able to say 1-2 words
Obviously, this is highly subjective as it’s based upon one’s perception of intensity. A “talk test” is often used to cross-check the assessment if the athlete is actually within the specified range. What might be an RPE of 6 for you could be a 9 for your friend.
Benefits of RPE
- This is a subjective measurement that is highly individualized. Specifically with trail- or ultra-running, there are often so many moving variables (elevation change, altitude, terrain, temperature changes, core temperature fluctuations, caffeine intake, emotional responses, dehydration, etc.) that to prescribe a specific HR range to maintain can sometimes be a wildly moving target. For instance, if you aim to maintain a specific heart rate when descending a steep climb, it could lead to injury due to excessive impact especially if you haven’t trained adequately on descents. Thus, using RPE allows the athlete to maintain a self-assessment of their effort and adjust according to subjective data (e.g. breath, intensity, etc.).
- Additionally, using RPE on days when you’re feeling “bleh” can avoid the chance of perpetuating overtraining or fatigue. Some might call this as a way to do “feel-based” training.
Drawbacks of RPE
- Since this is a subjective measurement, the actual RPE can become skewed when muscles become fatigued. You might feel as if you’re going at a 8/10 RPE but your heart-rate is indicating otherwise. Having an objective measurement (i.e. HR monitor) for longer-duration events can be a helpful indicator to press harder.
What are Heart Rate (HR) monitors?
Heart rate monitors offer objective data from a workout (i.e. staying within a particular “zone”). There are a number of HR monitors that exist today: a wrist watch, armband, and chest strap. The validity behind each of these will look different (e.g. a wristwatch will often display inaccurate data). Obviously, watches are very useful for other data but utilizing a wrist-based heart monitor will often give you glitches so it may be worth investing in a separate device (e.g. armband or chest strap) to give more accuracy and spare the frustration.
“Zones” is a term that often gets thrown around when athletes are aiming to stay within a HR range. To further complicate matters, a range of zone models exist which differ from another –the most common being the 3-zone and 5-zone models– so be sure to take a closer dive into which model you intend to use.
Benefits of HR monitors
- Imagine you’re several hours into a race and the fatigue is starting to build but your HR monitor is showing a lower HR than preferred. This can indicate that you can pick up the pace because fatigue is starting to cloud your overall perception of effort. It feels like you’re working a lot harder, but in actuality your cardiovascular system isn’t matching your high RPE.
- Alternatively, if you’re given an easy/conversational-pace day, using a HR monitor can keep you accountable from going too fast. Think of HR as a speed limit for these easy/conversational run days.
- HR monitors can be a very useful tool for cross-training days especially if you’re wanting to stay within a certain zone to maintain cardiovascular benefits.
- Assessing HR at rest can be useful to gauge how the body is recovering after a race or during peak training block. Typically as an athlete builds more fitness, the resting HR will lower and this indicates the heart’s stroke volume is increasing. It is important to recognize that if your resting heart rate is substantially low or high, this might be an indicator of overtraining syndrome and/or fatigue.
- Lastly, another benefit of utilizing HR is to assess the HR when doing your workout. If you’re reaching the targeted HR zone during a run (after accounting for cardiac lag, as described below), take note. Your depressed HR might be due to a lack of recovery. Similarly, your HR not lowering to your normal resting HR after a workout may also indicate under recovery.
Drawbacks of HR monitors
- For starters, I strongly recommend not using a wrist-based HR monitor as a valid measurement of HR. Several variables can significantly impact wrist-based readings like interference with the sensor, placement of watch, temperature, skin tone and more.
- Secondly, you will need to recalculate your zones as your fitness changes to keep them accurate. This article won’t go into zone calculating: go read Matt Fitzgerald’s 80/20 Rule if that’s your jam.
- Most notably, if you find yourself becoming obsessed with numbers to an unhelpful degree (e.g. constantly checking your watch) and it’s taking away from the enjoyment from running rather than adding to it, this can be a slippery slope. Additionally, this over-fixation on HR can lead to stress which will also impact your HR – a real double whammy. So, RPE or heart rate? In this case, I would highly recommend only looking at HR data after your runs and consider sticking with RPE.
- Cardiovascular lag (not cardiovascular drift) occurs when you start exercising and your heart-rate isn’t in the desired range. This happens to just about every one of us. It’ll often display more accurate readings after 25-30 minutes of steady movement.
- Cardiovascular drift is the gradual increase of HR over a workout. This accounts for the rise in core temperature and decrease in heart stroke volume. A runner may notice that their heart rate continues to increase during a longer, steady-state run but their respiration rate and effort level feel the same. Staying within a specific HR range may result in underperforming if you slow down unnecessarily to stay within the zone.
How should I use RPE and HR? Can I use both?
You absolutely can! Knowing when to use RPE or heart rate depends on the context of when and how to use it. Obviously, running on trails vs. road vs. track is very different so take that into consideration. My recommendation is when doing your conversational/easy-paced runs (RPE 5-6) or moderate-intensity (RPE 7-9) runs, allow yourself to use RPE for the first 30 mins to maintain the desired intensity. Thereafter, check your HR even now and then to see where it’s at, but still maintain a close gauge on your RPE. Obviously, this might show a wide HR range depending on the many variables (especially if you’re running on trails), but over time you might find some trends that correspond to both HR and RPE.
For high-intensity runs, start with your desired RPE (e.g. 10). Perhaps you also consider aiming for a specific pace to target rather than aiming for HR. You can take HR into account, but keep in mind that cardiac lag will occur and very short intervals (1-3mins) don’t allow ample time for the HR to reflect accurately.
Further Readings & Resources
UESCA Ultrarunning Coaching Course by Jason Koop
Kelsey McGill is a UESCA-Certified Ultrarunning Coach with Team RunRun. She has 10+ years of experience in coaching all levels and ages of runners, specializing in trail running and ultrarunning.
