Name of Gear: COROS Heart Rate Monitor

Gear Category: Accessories/ Technology (heart rate monitors)

*What the COROS Heart Rate Monitor looks like when not being worn.*

Typical Price: $79

Where to Buy: coros.com, rei.com, skimo.co, backcountry.com, runningwarehouse.com

Best Use:

Athletes are always in search of wearables that will provide more data! However, metrics mean little if they aren’t accurate. Wrist monitors on today’s watches have come a long way, but there are still large inaccuracies and anomalies that can occur. For example, when I grip a trekking pole, my watch will often read a low heart rate (HR) regardless of intensity level. Chest straps have long been the standard option for athletes who desire the most accurate HR data. Often they can be paired with a watch to make the real time HR readings accessible in action. That said, some folks, myself included, find wearing a chest strap to be uncomfortable at best or, at the worse, a recipe for chaffing. Additionally, chest monitors can interfere with avalanche beacon signals. This makes them risky for both skimo athletes and runners who enjoy high alpine adventures in the snow.

How?

The COROS Heart Rate Monitor provides a more accurate reading than wrist monitors while avoiding the shortcomings of the chest strap outlined above. This low profile heart rate monitor (HRM) is mounted on a soft elastic band and fits comfortably around the bicep of the user. Yes, the bicep! The HRM activates automatically once on the athlete’s arm. Then, after the initial set up, syncs to most watch brands and devices via Bluetooth (it doesn’t have to be another COROS product). The location on the bicep makes the device hardly noticeable to the user, decreases chafe probability and mitigates the interference issue with an avalanche beacon.

When? Where?

The COROS Heart Rate Monitor can be used in any situation where an accurate HR reading is desired. This includes roads, trails, long runs, races, training, etc. The only scenario I can think of where this monitor might not be a good fit is in a 200+ mile race due to the limit of 38 hours of active battery life. However, this is a highly specific situation and 38 hours is plentiful for most users. While the HRM is perfectly fine in rainy, wet conditions, it’s not suitable for swimming with as Bluetooth signals don’t carry underwater.

*TRR Coach Dandelion running with her COROS Heart Rate Monitor on her left bicep. PC: Damien Scott*

Sizing:

True to size.

Additional Sizing Comments:

The standard band is easy to adjust and fits a large variety of arms. There is also a large size band for athletes who require more volume. In either case, I suggest first adjusting the band snuggly, but not too tight, with your arm bent as though you were doing an arm swing while running. Micro adjustments can then be made from this point. I have found that sizing the band with your arm straight does not account for the increase in bicep size when the arm is bent. Therefore, it can end up being too tight.

Comparison to Previous Models and Other Brands:

Arm band heart rate monitors are relatively new developments. This COROS Heart Rate Monitor is the first, and most popular, model available. Other options include the Wahoo Tickr Fit and Polar Verity Sense, though I haven’t tested or heard much about them. All three come in at a similar price range of $79 to $99.

Durability and Accessibility:

I have been using the COROS Heart Rate Monitor for about 9 months during both training and ultra distance races. It has accompanied me in temperatures ranging from -20F to 102F (that’s -29C to 39C) and performed without issue within that range. It was subject rain, hail, dust and a variety of other harsh environmental factors. Aside from the elastic band getting dirty there is no noticeable wear on the device itself. (The band can be easily washed with soap and water.) A new band can be purchased for $25 in a different color if desired or if the elastic wears out over time, though this hasn’t happened to mine.

Changes for the Next Model:

A battery indicator on the device would be handy, but it is certainly not imperative. My watch does give me an alert when the heart rate monitor battery is very low. But it would be nice to know before it is “mission critical.”

Yes, absolutely! I often recommend the COROS Heart Rate Monitor to the athletes I coach and to friends who are looking for a more accurate heart rate monitor and/or do not care for chest straps.

Keeping it Honest – Did You Get This Gear for Free?

I did not get this device for free nor do I currently receive any compensation for recommending/reviewing this product.

Dandelion Dilluvio-Scott is a multisport outdoor athlete, ultra-runner and certified coach. She is passionate about collaborating with driven athletes who love to explore, train and play outside.

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.

RPE or heart rate? Here's Coach Kelsey using RPE to race Hood Hundred. — *RPE or heart rate? Here’s Coach Kelsey using RPE to race Hood Hundred.*

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.

*Coach Kelsey wears the Coros armband HR monitor (see left arm) while running the Three Finger Jack Loop in Oregon. PC: Kaysen Brennan*

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.