Let’s take a deep dive into some of the heart rate issues every endurance athlete has probably encountered

Photos by Bono Tsang, Sergio Souza, and Run 4 FFWPU/Pexels

Heart rate-based training has been a mainstay concept these past years. It’s a potent, easy, and cost-effective way of approaching training. In essence, it’s about staying within a particular HR value for different types of sets and workouts. But as simple as it sounds, some people still find it a bit difficult to execute and maintain.

This is understandable as there are a few quirks and peculiarities regarding this type of training. In this article, we’re going to talk about the common problems athletes encounter when it comes to heart rate.

Zones don’t line up

When you first use your watch or computer, it automatically presents you with default zones based on your age. While this is a fair estimate for the entire population in general, oftentimes, people notice their default zones don’t line up with how they feel. This is because formula-based HR zone calculations are usually not that accurate. There are a lot of factors influencing individual HR values. Genetics, gender, and fitness level are a few examples. The solution is simple. You need to do tests to help align your zones.

Heart rate-based training is about staying within a particular HR value for different types of sets and workouts

The most common test would be to do an LTHR (or FTP) test but this has its own set of problems. In a nutshell, you need to have pretty good fitness and motivation to go all out for 20 to 30 minutes and you also need to pace it perfectly.

From my experience working with athletes, the best way to do it is through a lactate test. This test, which I do in my lab, is a more tolerable, guided, and powerful way of establishing zones. Not only does it give you your zones, it also helps determine the type of training you should emphasize.

Heart rate is erratic or inconsistent

“Garbage in, garbage out” is a common term in data and computer science. What this means is that without a proper way of measuring data, it’s hard to establish the right trends and direction. This is the same for heart rate measurement: It should be done correctly.

The most common mistake is the use of wrist-based sensors. There are a few issues regarding this. Firstly, wrist sensors usually only use two or three LEDs and this makes measurement less robust. Secondly, these watches jiggle around when you run. Small movements and changes in the position of the sensor drastically affect HR measurement. This is why you see spikes and drops during faster intervals. And finally, there is usually less blood flow passing through the back of the wrist compared to the upper arm or torso. Since LEDs measure how blood passes through tissues and capillaries, lack of blood flow becomes problematic when it comes to HR measurement.

A better alternative is to use chest or arm-based sensors. These prevent the aforementioned problems easily. Other watches like Polar have more LEDs and employ contact sensors to aid in improving accuracy.

It’s difficult to hit the right target

This is a multifaceted problem that needs to be addressed across different fronts. Firstly, it might be as simple as not having the right zones (as mentioned in the first point above). However, it might also be because the athlete doesn’t allow the HR value to stabilize first. There’s such a thing called heart rate delay. This means that it takes a while for HR to catch up to a particular intensity (compared to speed, pace, or power). This can be seen in HR graphs: a shark’s fin profile is common for intervals because there’s usually a two- to four-minute delay before HR creeps up to a more stable number.

My advice is to not chase the numbers. Instead, hold an effort you think is suitable for the goal and make minor adjustments as you go along. It takes experience and patience but without using power-based training, this is the only way of nailing it.

Don’t chase numbers. Instead, hold an effort you think is suitable for the goal and make minor adjustments as you go along

Another possible reason why it’s hard to hit target values is fatigue. There are two main types of fatigue. The first is muscular fatigue. When your muscles are tired and consequently weak, it’s hard to stress your cardio enough. The weak link is your ability to push and go harder. As a result, your perceived exertion is high but you’re not straining your cardio enough. The solution is simple—rest. Usually, once you rest your body enough, you’ll be hitting those values once again.

However, a larger cause for concern is systemic fatigue. This can also come in two ways. Acute fatigue (and/or dehydration) means your HR goes up rather quickly and results in elevated HR values even for relatively easy intensities. This, in turn, makes it challenging to stay within a lower aerobic zone. Chronic fatigue, on the other hand, is a bigger problem that seems counterintuitive. This type of fatigue results in lower HR values across the board and makes it difficult to hit higher zones (similar to muscular fatigue). If ever you do get to raise your HR, it is unsustainable and is usually succeeded by rapid drops in HR between intervals. These are red flags that point to prolonged overreaching or even overtraining. The solution is to unload, destress, and focus on regenerative workouts.

Heart rate drifts

If you’ve ever noticed that HR increases for a steady effort, you’re not alone. This is a common observation among athletes who take zone training to heart.

To explain this, we need to understand that our body has a limited number of muscle fibers at its disposal. Most of the time, for aerobic zones and longer intervals, it prefers aerobic muscle fibers due to their efficiency and low metabolic cost. As these muscle fibers fatigue, they have to be subbed out for less efficient (more anaerobic) ones. The metabolic cost rises, which results in an increase in carbohydrate expenditure, rising lactate values, and higher heart rate values. This, albeit uncomfortable, can be thought of as part of the growing pains of getting stronger. Over time, as these underutilized fibers gain more experience and aerobic fitness, they become more efficient aerobic fibers.

When people see their HR increase for a steady effort, the common response is to lower intensity so HR goes down. While there is nothing wrong with this and is often the safe way of approaching such a phenomenon, I find it’s good to also hold the increasing HR (as long as the pace or power is the same) for short durations (e.g. towards the end of a set or a workout). Not only does it help convert more aerobic muscle fibers, it also simulates what one would feel towards the end of a segment or race when fatigue starts to set in.

In closing, heart rate is an essential tool in any endurance athlete’s arsenal. It gives us a peek into the state of our physical well-being and fitness. Hopefully, with the help of the topics we discussed here, you will be better equipped to make the right decisions and adjustments in training and racing.

Have some training questions, feedback or suggestions for future articles? Drop a note in the comments section below or on Facebook, Twitter or Instagram.  You can also get in touch with Don directly here.