COROS Coaches: Marathon Intensity Zones

As part of our COROS Coaches initiative, we recently received a question about intensity zones and the best one to choose from when training for a marathon. Let’s take a dive into our analysis so you can benefit from our coaching insight and improve your own training journey! The topic breakdown is followed by our full coaches’ analysis and feedback on the athlete’s question.

If you would like your own training questions answered, send us an email at and we’ll be happy to share insights!

COROS’ Intensity Zones

As a COROS user, you have access to multiple intensity-zone models to assist you in your training. Although none of those training tools are considered a gold standard, they all have pros and cons for you to choose and benefit from them depending on your objectives as an athlete.

Threshold Heart Rate and Pace Zones from EvoLab

Intensity Zone Example

If a hypothetical athlete with the given metrics (HRmax = 200; Resting HR = 50; Threshold HR = 170; and Threshold Pace = 6’00″/mile) were to run at 80% intensity, here are the values they would get depending on the intensity-zone model chosen.

Intensity-zone modelBased on% IntensityAthlete’s value
HRmaxHRmax80%160 bpm
HR ReserveHRmax & Resting HR80%170 bpm
Lactate Threshold HRThreshold HR80%136 bpm
PaceThreshold Pace80%7’30″/mile
  • HRmax: This model provides a direct fraction of your HRmax, ideal for new users who are getting into fitness.
  • HR Reserve: This range between your lowest and highest HR can provide a more personalized model for training enthusiasts who wish to improve their general fitness.
  • Lactate Threshold HR: This model separates the aerobic to the anaerobic intensities thanks to the threshold HR. It is therefore ideal for athletes who require quality sessions at higher intensity.
  • Pace: This model can be beneficial for runners with a specific racing strategy or for short high-intensity workouts when heart rate struggles to keep up.
Short high-intensity intervals where HR-zone models would not have been useful

Coaching Tip

Although the Pace-zone model is often used on flat road surfaces, you can now use the new Effort Pace-zone model that will allow you to complete your high-intensity bouts on hills!


An athlete who currently trains for their first marathon has an objective of a sub-4 hour race. This athlete just began a COROS’ Training Plan which includes both heart rate and pace zones.

Training-related Question

Which intensity model should I focus on during training days and race day?
Coaches’ Feedback

Before diving into which specific zone should this athlete focus on during training/race days, let’s differentiate the pros/cons of HR vs Pace.

  • Why you should use HR-zone models? See your HR as a car engine. The higher the pulse, the more the engine has to work. Some workouts are HR-focused, which means that they are aiming to adapt the engine and make it better.
  • Why you should use Pace-zone models? Now see pace as how fast your car can go. It is based on the biomechanics of your body. The workouts that are pace-focused are aiming to adapt the car (here the body) to function at a certain speed.
Workouts created using 2 different intensity-zone models
What Are the Demands of a Marathon?

Because a marathon is a long-distance event at constant intensity, we require our body to function at the highest intensity it can sustain for this amount of time. This table below roughly estimates in which pace zone most marathon runners complete their race depending on their fitness level.

Athlete’s Marathon LevelPace Zone During Race Day
4+ hoursAerobic Endurance (Zone 1)
3-4 hoursSlow-end of Aerobic Power (Zone 2)
2-3 hoursFast-end of Aerobic Power (Zone 2)
The fastest one can run a marathon, the closer they will get to Threshold (Zone 3)

Coaching Tip

Whenever you are preparing for an event, ask yourself “what will my body be required to do during this event?”. This way, you can quickly grasp the energy demands of the event and train based on them.

In the end, it’s okay if you use multiple zone models throughout training due to their ability to serve different functions. During racing, athletes should utilize the pace-zone model if time oriented, or hr-zone model if unsure on time and want to focus on effort. Remember both models are useful but should be selected based on your goals!

Remember that your car (body) can’t go as fast (pace) if the engine (heart rate) is not working properly. Always listen to your heart and don’t hesitate to take your foot off the pedal once in a while to ensure intensity is well maintained, and have fun!

Resting HR fluctuates considerably more than Threshold HR

If you would like your own training questions answered, head over to our COROS Coaches Blog for steps to submitting your questions!

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