The original article was published for the RunTriMag on October 14th, 2024. Access here: https://runtrimag.com/measuring-your-runs-by-heart-rate/
As a coach, I often get the same questions: “I don’t understand my heart rate zones,” “Why does my heart rate seem high when I’m running easy?”, “Why can’t I ever hit Zone 2?” or “Why do I struggle to hit my max zone (Zone 5)?” Many runners and cyclists get stuck trying to match their heart rate (HR) zones to what their smartwatch or apps like Strava say. However, the truth is that without proper testing, your real heart rate (HR) zones might remain a mystery.
Let’s dive into the pros and cons of measuring your runs by heart rate versus perceived effort, and explore the factors that affect HR, testing options, and how you can get more accurate data to guide your training.
The Heart Rate Formula: Where It All Started
Most smartwatches and apps calculate your maximum heart rate using the formula: Max HR = 220 – Age in Years. This formula, developed by Fox and Naughton in 1971 [1], was originally created to estimate the highest safe intensity level during exercise based on age. Back then, the relationship between exercise and heart health was still being explored. The formula aimed to provide a guideline for physical activity that minimised the risk of “cardiac catastrophe” while offering health benefits.
Although the formula works as a general guideline for unfit populations, it’s not highly accurate for everyone and can underestimate max HR in fitter populations. Exercise produces cardiovascular remodelling, making your heart more efficient [2, 3]. Research shows it can be off by as much as 12 beats per minute (bpm), especially in younger and older individuals [4]. Furthermore, it doesn’t account for genetics or how your body adapts to training.
Factors Affecting Heart Rate
Several factors can influence your heart rate during exercise, making it seem like you’re in the wrong zone when, in reality, you’re not. Here are some of the most common ones:
Fatigue: If you’re tired, your heart rate may be higher than usual, even during easier efforts. Fatigue impacts how your body responds to exertion.
Environment: Heat, humidity, and altitude can make your heart work harder. For instance, running in hot weather increases your heart rate significantly because your body is also working to thermoregulate.
Hormonal Fluctuations (Women): Hormones related to your menstrual cycle can influence heart rate. For example, higher progesterone levels during the luteal phase can lead to increased heart rate.
Fitness Level: As you become fitter, your heart becomes more efficient. Over time, your heart rate at a given pace will decrease, which can shift your training zones.
Given these factors, it’s easy to see why solely relying on HR data from your watch might not give you the full picture.
The Gold Standard: Laboratory Testing
For the most accurate insight into your heart rate zones, laboratory testing is the gold standard. These tests involve using specialised equipment and offer highly precise data on your maximum HR, and ventilatory and lactate thresholds, which are then matched to pace and perceived effort. Here’s a breakdown of the main lab tests:
Lactate Threshold Testing: Lactate threshold refers to the point at which lactic acid builds up in the bloodstream faster than it can be cleared. Knowing this can help set your zones.
Maximal Lactate Steady State (MLSS): This test identifies the highest pace at which lactate production and clearance are balanced. It is another key factor in determining heart rate zones, particularly for higher-intensity efforts and is an ideal test for endurance athletes.
These lab-based methods offer pinpoint accuracy but can be expensive, time-consuming, and aren’t always accessible for most athletes or may not be suitable for all individuals.
Field Testing Methods: DIY Solutions
If lab tests aren’t an option, you can estimate your zones using various field tests. These are practical, do-it-yourself (DIY) alternatives that don’t require advanced equipment and can provide an estimation. (Note: this test can be done for runners using pace and cyclists using power.)
30-Minute Field Test
After a warm-up, run (or cycle) at maximum sustainable effort for 30 minutes. Your average heart rate during the last 20 minutes will give you an estimate of your threshold heart rate, which is about 90% of your max HR. From here, you can calculate your training zones.
It’s better to perform this test solo. This way, you’re more likely to run at a pace close to your 10K race pace without pushing too hard. This test is more accurate than shorter versions, such as the widely used 20-minute field test. This is because lactate levels typically take between 30 and 70 minutes to stabilise, so shorter versions can lead to an overestimation of the true threshold.
For coaches using TrainingPeaks, this is a handy test to estimate zones using lactate threshold heart rate (LTHR) and the Joel Friel method for running to calculate zones.
1-hour Steady Effort
This test is very useful for measuring endurance capacity, making it ideal for long-distance runners and cyclists. In this test, after a warm-up, you would run or cycle for an hour at a steady, easy-to-moderate effort, which typically falls within Zone 2 or Zone 3, depending on your pace. This test is most suitable for well-trained individuals, as it requires a high level of fitness to sustain the effort. It is an excellent tool for tracking performance improvements by comparing the distance travelled and the heart rate during the effort over time.
Incremental Testing or Léger-Boucher Test
This test is easy and useful for measuring the velocity at VO2max (vVO2max). In this test, after a warm-up, you need to increase the speed every two minutes over five stages. Your heart rate at the highest effort from the last completed stage can be matched to the vVO2 Max, which is in the upper training zone (Zone 5). This test is better performed on a treadmill or track.
The Talk Test
This is a simple but effective method for gauging your effort, which can be matched to training zones. It’s actually one of my preferred DIY methods, and if done properly, it’s accurate. To do so, recite short sentences while running, increasing your pace every two minutes.
Zone 1-2 (Easy – below threshold): You should be able to converse with ease.
Zone 3 (Moderate – at threshold): You can still talk, but completing full sentences becomes challenging.
Zone 4-5 (Hard – above threshold): Speaking is difficult, and you can only manage short bursts of speech due to heavy breathing.
Working with a Coach
For many athletes, working with a coach is the best way to ensure accurate training zones. A coach can analyse your data from platforms like TrainingPeaks and adjust heart rate zones as your fitness evolves. They can also interpret your heart rate data within the context of your overall training, taking into account factors like fatigue, the environment, and how your body responds to different workouts.
By combining data with the insight of a coach, you can better understand your performance and avoid being misled by an over-reliance on technology.
Conclusion
Whether measuring your runs by heart rate or effort, understanding the limitations and nuances of both approaches is key. Heart rate training is valuable, but it’s not perfect. Factors like fatigue, environment, and fitness level can all influence heart rate, so it’s important not to get too caught up in what your watch tells you.
For the most precise data, lab testing is ideal, but field tests provide an alternative. To ensure comparability, always use the same route and conditions for your tests, and make sure you’re well-rested beforehand to avoid underperformance. Regardless of the method you choose, the key is consistency and listening to your body.
REFERENCES
1. Fox, S.M. and J.P. Naughton, Physical activity and the prevention of coronary heart disease. Preventive Medicine, 1972. 1(1): p. 92-120.
2. Weiner, R.B. and A.L. Baggish, Cardiovascular Adaptation and Remodeling to Rigorous Athletic Training. Clin Sports Med, 2015. 34(3): p. 405-18.
3. Mihl, C., W.R. Dassen, and H. Kuipers, Cardiac remodelling: concentric versus eccentric hypertrophy in strength and endurance athletes. Neth Heart J, 2008. 16(4): p. 129-33.
4. Robergs, R. and R. Landwehr, The surprising history of the "HRmax=220-age" equation. International Journal of Online Engineering - iJOE, 2002. 5.
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