By Jim Rutberg, CTS Coach and co-author of “Training Essentials for Ultra- running.”
Heart rate monitors were one of the first technologies runners could use to gauge training intensity, and over the past 35 years technologies like GPS watches, accelerometer-equipped foot- pods, wearable fitness trackers, and running power meters have enhanced the data available to runners. The range of available tech has many runners wondering whether the good ole’ heart rate monitor is still useful?
The short answer is yes. The longer answer starts by saying heart rate has advantages and limitations for different athletes. The original premise behind heart rate training is that heart rate increases and decreases in response to the body’s demand for oxygen. At rest, those demands are light, so heart rate is relatively low. As you go from rest to walking to running, oxygen demand increases, so heart rate rises to deliver oxygenated blood to working muscles. Breathing rate also increases, although respiration rate is driven by the amount of carbon dioxide in the blood (which also rises as more oxygen is used to produce energy).
An athlete’s heart rate can be correlated with intensity or pace, which is the basis of establishing heart rate training zones or ranges. Using a laboratory test or field test, or even data analysis within some watches and apps, you can find your maximum sustainable heart rate or your heart rate at lactate threshold. This is not your maximum heart rate, but rather the heart rate associated with the fastest pace or highest intensity you can sustain for a prolonged period (10-20 minutes or up to an hour depending on conditioning). Training software can then apply percentages to that value to establish training zones. These zones delineate the heart rate zones for recovery, aerobic endurance, lactate threshold, and above-threshold efforts.
Sounds great, right? But there’s a problem.
Heart rate is a response to the work you’re doing, not a direct measure of work.
As such, it’s influenced by a wide range of factors. When you’re hot, heart rate typically increases. Caffeine and other stimulants increase heart rate. Improved fitness can reduce heart rate response at a given pace. Fatigue can suppress heart rate, and certain medications can either increase or decrease it. Hydration status can also push it in either direction. Nervousness, stress, sadness, anger – even love – can all affect heart rate. And more than one of these factors can influence heart rate at the same time!
So, then heart rate seems pretty useless, right?
No, the variability in heart rate response means is that you have to look at heart rate in context with other information. The simplest way to do that is with the triad of heart rate, pace, and perceived exertion.
Over the long run (no pun intended), heart rate, pace, and perceived exertion will all correlate to create snapshots you recognize as “easy,” “endurance,” “hard” or “race pace,” “only sustainable for a few minutes,” and “BEAR!” (or “MUGGER!”, depending on where you’re running). Let’s say a 10:00-minute mile pace on flat ground for you typically feels like a 5-6 on a 1-10 scale where one is walking, and 10 is “BEAR!”, and your heart rate at that pace is about 150 beats per minute. These three data points are completely individual to you, but would likely combine to describe a sustainable endurance effort. If you’re resting appropriately between runs and training at an appropriate workload, that snapshot should stay relatively constant from run to run.
Fixing Problems in Real Time
The great part about using the triad of heart rate, pace, and perceived exertion is that when they indicate something is off, you can often use the same information to fix the problem. Here are a few examples, although I have to caution, everybody is different, and these scenarios and solutions may not exactly match your needs.
Example 1: 140 bpm, 10:00 min/mile pace on flat ground, PE of 7 out of 10
Perceived exertion is higher than normal at a pace that should feel easier, and heart rate is lower than normal for the pace and perceived exertion. Heart rate may be suppressed by fatigue, meaning the effort required to achieve a 10:00 min/mile pace feels harder than it should. In this scenario, pushing harder to raise the heart rate to 150 will feel way too hard and is not advised. It is more likely you need some rest.
Example 2: 165 bpm, 10:00 min/mile pace on flat ground, PE of 5-6 out of 10
Heart rate is abnormally high given the pace and exertion. Assuming 165 is a still a reasonable heart rate for you*, you may be able to keep running at this pace. At the same time, you want to figure out potential causes for the high heart rate. Is it hot out? Is your skin or core temperature elevated (even indoors)? Are you dehydrated? Did you eat or drink something with a lot of caffeine or other stimulants? When heat and dehydration are likely causes, take steps to fix the problem by slowing down, dousing yourself with water, draping with cold towels, and consuming cold fluids.
*An excessive and abnormal spike in heart rate, pain in your chest, nausea, and lightheadedness are symptoms of arrhythmia. Call 911.
Where Perceived Exertion Trumps Heart Rate
Just as it’s important to know how to leverage the information heart rate provides, it’s also important to recognize when it’s not likely to be a reliable gauge of intensity.
Heart rate is a response to actual work, and there is a lag between when you do the work and when you can see that work reflected in your heart rate. On flat ground, rolling hills, or a treadmill the lag is less of a problem. On trails, the grade, surface, and technical challenges change so quickly that heart rate can’t keep up. When you charge up a short, steep rise on the trail, your heart rate will still be rising as you’re running down the other side. Similarly, heart rate won’t fall as much descending a technical trail compared to cruising downhill on a smooth park path.
Heart rate at any given effort level increases as you travel to higher elevations. This is typically not noticeable until you surpass about 5,000 feet above sea level, but as you go even higher, the effect gets progressively greater. Again, a lot of factors – in addition to the normal ones – combine to determine your individual response to altitude, including fitness level, acclimatization, and hydration status.
For trail running and trips to altitude, perceived exertion is the best available intensity gauge. When athletes ask about using heart rate for pacing at the high-altitude 100-mile Leadville Trail 100 ultra- marathon, I ask them to determine what their maximum sustainable heart rate and pace should be at 11,500 feet above sea level on a 22% grade gravel trail, 17 hours into the race, at night in a cold thunderstorm? It’s an extreme example, but entirely plausible for a Leadville 100 competitor and a good illustration of the importance of perceived exertion in challenging and variable conditions.
Jim Rutberg is a Pro Coach for CTS and co-author of 8 books on training and sports nutrition, including “The Time-Crunched Cyclist” and “Training Essentials for Ultrarunning”. To get started with personal coaching, bundle CTS Coaching with a Wahoo KICKR KICKR SNAP, or ELEMNT.