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For years I have used my heart rate to measure my effort while out trail running. However, there have been times when I’ve forgotten to charge my watch or my heart rate monitor hasn’t worked properly. That led me to wonder whether I could reliably use perceived exertion as an alternative. Let’s take a closer look at how these two methods of measuring your effort compare so that you know what to do if you are out on the trail and your favorite gadgets stop working the way you want them to. What Is Rate Of Perceived Exertion [answer target] Your rate of perceived exertion or RPE is a way of gauging your effort based on how difficult your run feels. The best part of using RPE is that there are no electronic gadgets to purchase or use. The trouble with RPE is you have no data to share with your coach or measure improvement. When you use your rate of perceived exertion there is no lag time of waiting for the data from your effort to catch up. You know exactly how much your run is taxing you and exactly how out of breath you feel. Novice runners often struggle with using their rate of perceived exertion to measure their effort while running as they have not yet built up the experience to truly know how the different effort levels feel in relation to each other. There are various factors that can affect your RPE and make a run feel more taxing at the same pace. The most obvious of these is the gradient of the trail. Uphill trail running always feels harder than running on flat trails and slight downhills. Steeper downhill running becomes taxing on my quads after a while and that elevates my RPE. Similarly, your RPE will be higher on really technical trails where you are not able to build up much momentum. Hot weather and really cold temperatures make your trail running feel more taxing too. When I am training for a big event, my training is split into training blocks. As I get to the end of a heavy, high-volume training block I carry more and more fatigue from one day to the next. This makes my workouts feel harder than my data numbers would otherwise indicate. This makes my RPE higher for the same or even lower actual effort. A downside to RPE is the lack of accuracy. Even something as simple as your mood can affect how easy or hard a run feels. Recording a run in your training journal can be difficult as how you feel after you have finished your run and completed your warm-down can be different from how you felt in the middle of your run. Without the data from a previous run, it is hard to replicate a training session to have the same intensity as you have done before. Likewise, it is very tricky to communicate the results of a run to your coach, as well as understanding exactly what your coach needs from a particular training session. You or your coach won’t be able to measure your improvement and so you won’t be able to easily adapt your training based on how your fitness or form is changing. What Are The Pros And Cons Of Using Heart Rate To Measure Your Effort The key advantage of using heart rate to measure effort is that you have an accurate number to show you if you are going too hard or too easy during a run. Back when I ran more competitively I used to track my resting heart rate immediately as I woke up each morning. That would tell me if I was still carrying some fatigue from the previous day’s training. If my morning heart rate suddenly spiked up by over 10 beats per minute I knew that I was likely coming down with a cold, as the heart rate spike would almost always precede me getting a cold by about two days. Once I realized that connection I was able to prevent catching colds by taking a complete rest day on the day I noticed the spike in morning heart rate. After one rest day, my morning heart rate would return to normal and I could resume training without getting sick. During my longer endurance runs, I set myself an upper limit to my heart rate for that run. This means when the trail goes uphill or gets more technical I can see how much I need to slow down so that my heart rate can stay within my pre-selected range. One serious drawback of using heart rate to measure your effort is what is known as lag. When you increase your effort during a run, your muscles will send a message to your heart that they need more blood and oxygen. Your heart then starts beating faster in order to increase blood flow to those muscles. If the new blood flow is still not enough your heart rate will increase until it reached a level where you can deliver enough blood and oxygen to the muscles or alternatively your body will force you to slow down again. All of this takes time for your heart rate to balance out to your new level of effort. One area of training where this is really clear is when doing intervals for speed-work or hill repeats. When I get to the end of an interval my heart rate will still continue climbing even though I have stopped running at the end of the interval. What our middle-distance track athletics coach would do is use heart rate to measure how long we were allowed to rest between intervals. We would run our interval as hard as we could and rest till our heart rate dropped down to 120 beats per minute (we had to count 20 beats in 10 seconds). The moment our heart rate touched 120 beats per minute we had to start the next interval. How To Measure Your Perceived Effort While Trail Running When it comes to measuring your rate of perceived exertion there are two different scales you can use. The first of these is the Borg scale, created by Swedish psychologist Dr. Gunnar Borg for his work in treating cardiac patients during their rehabilitation. The Borg scale rates exertion from a level 6 for no exertion at all to a level 20 for maximum exertion. 67very very light89very light1011fairly light1213somewhat hard1415hard1617very hard1819very very hard20The Borg Scale When you first glance through the above table it might seem strange to create a scale that goes from 6 up to 20. However, just add a zero onto each of the numbers and you will see that a level 6 equates to a heart rate of 60 beats per minute, and level 20 means a heart rate of 200 beats per minute. Luckily for us, Dr. Gunnar Borg realized that his patients had difficulty accurately expressing numbers on a scale from 6 to 20. So, he revised his scale to create the Borg CR10 Scale that conveniently went from zero at the minimum to 10 at the maximum. 0nothing at all0.5very very light1very light2light3moderate4somewhat hard5hard67very hard8910very very hardThe Borg CR10 Scale The Borg CR10 scale works well from 0 to 5, the range where Dr. Borg’s patients needed to keep their efforts while exercising. Above 5 it becomes more difficult to accurately estimate CR10 effort because the exponential increase in blood lactate affects our thinking. This is where the breathlessness scale cones into its own. This is a scale of perceived exertion from 1 to 10. However, where a hard effort is a 5 on the CR10 scale, it is an 8 on the breathlessness scale because of how much easier it is to feel slight changes in an effort at easier levels. 1extremely light2very light3light4comfortable5moderate6challenging7somewhat hard8hard9extremely hard10maximum effortThe Breathlessness Scale When I raced cross-country at high school our coach used a very simple method of gauging our efforts during training. It was the talk/sing test. If we were able to sing while running we needed to push harder till we reached the point where singing made us breathless but we could still hold a conversation. Conversely, if just talking made us breathless we needed to slow down. I remember a story from a triathlon training camp in Leysin Switzerland, where the workout was a 2.5hr run at a conversational pace. About an hour into the run a car pulled up next to the group and it was head coach, Brett Sutton, shouting at everyone that this was a conversational pace effort so why was nobody talking. How To Measure Your Heart Rate Effort While Trail Running With the advent of GPS and smartwatches, we can see our heart rate on our wrists every waking moment of the day. There are two potential systems that you can use. The first and simplest is the heart rate monitor that comes built into your watch. It is known as an optical heart rate monitor and measures the fluctuations in pressure coming from your arteries that is caused by your heartbeat. To be able to work all the optic sensors need to be in contact with your skin at the same time. I find that this works best for checking my resting heart rate as I wake up in the morning. When I’m out running I often find that the watch moves on my wrist and I lost the heart rate signal. If I want the optics to work I need to make my watch strap so tight that I get pins and needles in my hand by the time I’ve run the first 3 or 4 miles. What I prefer to use when I’m out on a run is a chest strap heart rate monitor that works the same way that a medical ECG machine does. The chest strap measures the electrical impulses given off by your heart and thus gives a very accurate reading. The chest strap can be paired with either your GPS watch or with your phone. One thing that I have noticed with my chest strap is that when the battery starts running flat, the reading gets somewhat meaningless. A few years ago I was running in our provincial 10k championship and my heart rate seemed to be bouncing around between 95 and 235 beats per minute and multiple numbers in between. The next day I put a new battery in the strap and went for a run at the same intensity and my heart rate stayed between 137 and 149. How In-Tune With Your Body Are You Relating To Your Running Effort While it is great to have your heart rate data at your fingertips, it is equally important to teach yourself to run to your Rate of Perceived Exertion because it can easily happen that wither your GPS watch wasn’t charged or that the battery in your heart rate chest strap is flat like what happened to me in our provincial 10k championship. In these cases, your skill at knowing your RPE will save the day for you. A fun way to test and improve this skill is by either covering your GPS watch or putting it in the main pocket of your hydration vest. That way you can’t see the numbers on the screen of your watch even though it is recording. Then set out on a run at one of the intensities on the breathlessness scale and hold that intensity all the way through your run. After your run, download the data file from your watch and see how stable you were able to keep your heart rate just by using your RPE. I do this exercise when I’m out on my long run or on a recovery run. In other words, I never do this when I’m running intervals or hills. I find it a fun way to sharpen my RPE skills and keep my mind focussed on the run when I might otherwise be zoned out, thinking about other things. This new level of focus on slower recovery runs has drastically reduced the number of times I’ve tripped over rocks and roots while on easier runs.

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