If you feel like you're running at a snail's pace to stay in Zone 2 but your heart rate monitor (HRM) insists you're in Zone 4 or 5, you're not alone. This common issue can be confusing, but there are several reasons why your HR might be reading higher than expected. Here's the breakdown:
TL;DR:
Get a chest strap
Heart rate is influenced by many daily life factors
Do a field test to find your aerobic threshold
Consistency, consistency, consistency
Ultimately, RPE trumps monitoring your HR
Get a chest strap
Wrist-worn heart rate monitors (HRMs) are often inaccurate. The wrist is a challenging location for optical pulse reading due to the presence of tendons, which obstruct the optical view. Additionally, most GPS watches do not prioritize high accuracy for their optical HRMs. The wrist generates a lot of optical noise that the device's firmware must filter out to obtain a clear pulse reading, and this issue isn't much better on the underside of the wrist.
Furthermore, the motion of your wrist while running introduces additional noise. Unless the watch is secured very tightly, the arm's swing can complicate accurate readings for the optical sensor.
In contrast, a chest strap reads the electrical signals produced by your heartbeats, encountering minimal noise that needs to be filtered out. Movement doesn’t affect its accuracy, making it easier to obtain reliable heart rate readings. Even inexpensive chest straps can be more accurate than high-end GPS watch HRMs.
If chest straps are uncomfortable, consider using a dedicated optical armband HRM. These devices are worn on the forearm or upper arm, where they can optically read your pulse from a more accessible position under the skin, away from tendons. Because they are specialized for this single task, they tend to be as reliable as chest straps.
Daily factors
Your heart rate can fluctuate significantly due to various factors, causing as much as 15-20% variation from day to day. Influences include caffeine consumption, sleep quality, personal stress, daily circadian rhythms, temperature, humidity, and illness. For example, even during a light, easy zone 2 run, a chest strap might show your heart rate 20 beats per minute higher than usual.
Tips for more consistent readings:
- Reduce caffeine intake, especially in the evening
- Prioritize good quality, deep sleep
- Find effective ways to manage stress (though it's often challenging)
- Run in the cooler mornings if possible
- Establish a routine by training at the same time each day, which can help make heart rate readings more reliable
Determining your true Zone 2
You might also have your heart rate training zones set incorrectly. Did you do some math based on your max heart rate, or using your resting heart rate to find your heart rate reserve? Then you are using some arbitrary percentage boundaries which really don't align with our physiology.
If you want to find your true zone 2 boundary, the best way is to do a simple field test, as explained by Evoke Endurance:
- Run a very flat route (< 1% grade) or on a treadmill. This test cannot be executed on hills
- Warm up getting your heart rate up to where you think the top of your zone 2 boundary is
- Keep this pace for 1 hour
- Cool down
Take the average heart rate for the last thirty minutes of your test and divide it by the average heart rate of the first thirty minutes of your test. If your heart rate drifted:
- Less than 3.5%, you could have run harder
- Between 3.5% and 5%, you found your zone 2
- More than 5%, you ran too hard
For example, if the average HR for the first 30 minutes of your test was 145 bpm and it averaged 152 bpm for the last 30 minutes, then 152/145 ~= 1.048275862. Your HR drifted about 4.8% during that test. 145 is the top of your zone 2.
Execute this test every 6-8 weeks to keep an eye on your aerobic development.
Maintain Consistent Running Week-Over-Week
If you've taken a break from running due to injury, burnout, or other reasons, you might notice a higher heart rate when you resume training. This happens because of a loss of mitochondria in your muscles and the recession of capillaries from deep muscle tissue.
The same applies to new runners or those who aren't consistent with their training. An efficient aerobic system, essential for a low heart rate, requires a steady supply of oxygenated blood to working muscles. The efficiency of this process depends on the number of mitochondria and the depth of capillaries, both of which increase with regular, consistent training.
Therefore, it's crucial to run regularly, whether on pavement or dirt, adhering to a consistent schedule day after day, week after week, and month after month. You'll start to notice a drop in your heart rate after a couple of weeks, and over several weeks to months, you'll see your easy pace improving without a corresponding increase in heart rate.
Consistency is the key. Interrupting your routine or taking breaks will hinder your aerobic gains.
Embrace the Rating of Perceived Exertion (RPE)
Ultimately, how you feel during your run is more important than what your heart rate monitor (HRM) indicates. Due to daily heart rate variability, your HRM might show a higher heart rate even if you feel great. Should you maintain your effort or ease up to lower your heart rate? Trust your body's signals to make the right decision in the moment.
Here's a guideline for running in "zone 2" based on how you feel, without relying on an HRM:
| Zone | Breathing | Speaking | Sweating | | ---- | ---------- | -------------- | -------- | | 1 | Nose | Can sing | None | | 2 | Nose/mouth | Full sentences | Light | | 3 | Mouth | Short phrases | Medium | | 4 | Audible | Single words | Hard | | 5 | Grunting | Speechless | Heavy |
This isn't a one-size-fits-all guide. Some might manage hard efforts while breathing through their nose, while others may find it hard to breathe through their nose even during a walk. The above descriptions help you tune into your body's signals during a run.
As you become more attuned to your RPE, you'll find yourself checking your watch less often and paying more attention to your surroundings—nature, animals, people, city sights, and so on. Eventually, you might stop looking at your watch altogether. When you get home and someone asks, "Did you have fun on your run?" you'll be able to answer, "Yes!" with genuine enthusiasm.
Conclusion
Experiencing a high heart rate during what should be an easy zone 2 pace could stem from various factors:
- Inaccurate HRM readings
- Influence of caffeine, inadequate sleep, work stress, illness, etc.
- Incorrectly configured training zones
- Inconsistent running habits or being new to running
- Disregarding your actual physical sensations during the run
Exploring these factors can help pinpoint why your heart rate is elevated and guide adjustments in your training regimen.