Introducing Zone Training: It’s More Than the Heart Can Tell
Long before I knew anything about zone training, as a high school runner, my coach handed me training programs every month or two. These weren’t like the high-tech tools we have today—they were simple, handwritten plans, often scribbled with words like “Easy” or “Steady” to indicate intensity. On Sundays, I’d run for two hours, timing myself with an Ironman watch that could store over 100 laps, which was a big deal back then (I’m 35 now).
Fast forward to today, and running has evolved with a plethora of tools designed to enhance training and race performance. A few years ago, I upgraded to a Garmin watch, and suddenly, I was drowning in data. My watch now constantly updates me on my progress, while other gadgets like Whoop’s wristbands and Stryd’s running power meters add even more layers of information. The days of pen-and-paper training plans are long gone—now, data reigns supreme, helping athletes and coaches fine-tune training and optimize performance.
One of the most widely used frameworks in this data-driven world is heart rate zone training. This method organizes training intensity based on heart rate, which can be measured via the wrist, upper arm, or chest. By staying within specific heart rate zones, athletes can plan their sessions to align with their goals and current fitness levels. Understanding how to apply these zones is crucial for progressing toward a big race or adventure while managing rest and recovery.
This article is for those who want to make sense of heart rate zones and apply them to their own running. We’ll start by defining zone training, explore how the body responds at different intensities, and then discuss how to tailor training zones for your next training block.
What Are Heart Rate Zones?
Heart rate zone training is based on the idea that the body’s energy production changes depending on its rate of work. For example, the energy systems used in a 1-mile race differ significantly from those used in a marathon. Heart rate zones help runners spend the right amount of time at race-specific intensities, optimizing performance.
The number of zones can vary depending on the model used. Polar, for instance, divides training into five zones, each representing 10% increments of your maximum heart rate. Other models might use three or four zones or split them further. For simplicity, I’ll reference a 5-zone framework in this article:
| Zone | Name | Intensity | Use |
| 1 | Active Recovery | Very Light | Hiking, active recovery |
| 2 | Easy | Light | Easy days, medium/long runs |
| 3 | Aerobic | Moderate | Tempo work |
| 4 | Threshold | Hard | Strength-based intervals |
| 5 | VO2 Max | Maximum | Power-based intervals |
The Wandering Heart and You
Here’s the thing about heart rate during running: it’s not always a perfect indicator of effort. For example, during sustained efforts, your stroke volume—the amount of blood pumped per heartbeat—decreases as body temperature rises. To compensate, heart rate increases, a phenomenon known as cardiac drift. On hot days, this drift can make your heart rate seem higher than your perceived effort, leading to misleading data.
Additionally, emotions can also affect heart rate. A charged atmosphere, like a race day, can elevate your heart rate due to an increase in sympathetic nervous system activity. Experience level also plays a role. Seasoned runners often have a more efficient stroke volume, allowing them to maintain lower heart rates at higher efforts. In contrast, newer runners might see their heart rates spike more quickly.
Given these variables, it’s clear that heart rate numbers should be taken with a grain of caution. But if heart rate can sometimes mislead, how do we make sense of our training? Understanding how the body reacts at different intensity zones can help.
What Happens at Different Exercise Intensities?
Incremental exercise tests (IET) are used to determine how the body’s metabolic systems respond to increasing heart rate and pace. These tests can reveal how heart rate and energy systems interact as you move through different zones.
Rewind to high school biology and you’ll remember that the body has three types of muscle fibers: Type 1, Type 2a and Type 2x. Type 1 are typically referred to as “slow twitch”. These fibers are great at handling energy metabolism at low intensities, in those first two zones. Compared to Type 1 fibers, Type 2 fibers are able to produce more force, allowing you to reach higher intensities. One major adaptation to long term endurance exercise is the body’s conversion of Type 2 muscle fibers to the more fatigue-resistant and efficient Type 1 fibers.
At the beginning of a run, your parasympathetic nervous system relaxes its grip, allowing your heart rate to rise to about 100 beats per minute. As you increase intensity, the sympathetic nervous system takes over, boosting heart rate further to deliver more oxygen to your muscles. Initially, Type 1 muscle fibers handle the work, using oxygen to produce energy through aerobic metabolism. As intensity ramps up, Type 2a fibers join in, using glycolysis, which produces lactate as a byproduct.
When the body reaches the point where lactate production begins to outpace its clearance—known as ventilatory threshold 1 or the aerobic threshold—you’re typically in Zone 3. Training in this zone builds your aerobic engine without overwhelming your muscles with fatigue.
As you push harder, moving into Zone 4, you hit your lactate threshold, the point at which exercise becomes anaerobic. This is your aerobic ceiling, where the body struggles to keep up with the demands for oxygen, and lactate starts to accumulate faster than it can be cleared. Training at or slightly above this threshold can significantly improve your body’s ability to sustain higher intensities.
Finally, at maximum effort, you reach VO2 Max—your body’s maximum capacity to use oxygen. This is where the work feels hardest, and fatigue sets in quickly.
Which Zone, and When?
When planning your training, context is everything. Consider your experience level, current fitness, and target race or adventure when deciding which zones to focus on.
Zone 2 training is often hailed as the “golden” zone for distance runners. Many experts recommend spending about 80% of your training time in this zone, as it builds a strong aerobic base without risking mechanical breakdown. Early in a training block, most of your running should be within Zones 1 and 2, allowing your cardiovascular system to adapt safely.
Once you’ve built a solid foundation, you can start incorporating harder efforts from Zone 3. This zone is crucial for marathon training, where the intensity is higher, but still primarily aerobic. Workouts in Zone 3 might include tempo runs or long intervals at marathon pace. Workouts at this intensity help you build strength and endurance for race day.
As you progress, Zone 4—threshold training—becomes important, especially for shorter races like 5Ks and 10Ks. Zone 4 intervals help your body handle the demands of faster paces, improving your ability to sustain high efforts.
Throughout your training, remember that these zones are tools, not rules. Use them to guide your workouts, but be flexible and adjust based on how your body responds. The goal is to find the right balance that prepares you for your next running challenge.
In summary, heart rate zone training offers a structured approach to running that can help you achieve your goals. Whether you’re aiming for a marathon or just looking to improve your fitness, zone training has benefits for all runners. By understanding how your body responds at different intensities and applying that knowledge to your training, you can make the most of each run and set yourself up for success.
References
Power, S. K., Howley, E. T., & Quindry, J. (2008). Exercise Physiology: Theory and Application to Fitness and Performance. McGraw Hill: New York, NY.
Looking for more information about different training intensities? Check out: “Why Running Slow Helps You Run Fast with Coach Dan Lyne“.