REN can show helpful heart-rate insights in your workout details—like time spent in different intensity zones—using three optional metrics:
Max Heart Rate (HRmax)
Resting Heart Rate (RHR)
Threshold Heart Rate (THR)
These values can make heart-rate zone reporting more personal and accurate. But you don’t need them to train with REN.
How REN uses heart rate (and what it doesn’t use it for)
REN uses your heart-rate metrics to calculate and display time spent per intensity zone in the Activity Details of a workout (for example, how many minutes you spent in easy, moderate, or hard effort).
However, REN workouts themselves are based on pace—not heart rate.
Why? Because heart rate can be misleading, especially at higher intensities. In particular, heart rates above ~80% of your threshold can be influenced by things like heat, dehydration, stress, caffeine, poor sleep, or sensor noise. That can make heart-rate-based training feel inconsistent even when your fitness is improving.
So if you don’t know your HRmax/RHR/THR: no problem at all—you can still follow REN workouts normally and effectively.
Max Heart Rate (HRmax): how to estimate or find it
What it is: The highest heart rate you can reach during an all-out effort.
Option A: Use a simple estimate (quick and good enough)
A very rough but common estimate is:
HRmax ≈ 220 − age
orHRmax ≈ 208 − (0.7 × age)
These are averages across populations—useful as a starting point, but they can be off by 10–20+ bpm for individuals.
Option B: Use your real-world highest value (often better)
If you’ve done hard sessions or races while wearing a reliable chest strap, you can:
Look at your highest recorded heart rate from a recent all-out effort (like a finishing sprint or steep hill push).
Use that as your “observed HRmax,” especially if it’s repeatable.
Option C: Lab test (most accurate)
A supervised graded exercise test in a lab is the most accurate way to determine HRmax, but it’s not necessary for most runners.
Resting Heart Rate (RHR): how to measure it
What it is: Your heart rate when your body is fully at rest.
Best method (simple and consistent)
For 3–7 mornings:
Measure right after waking up, before coffee or getting out of bed.
Stay still for a minute.
Record the value and take the lowest or average of the week.
Using a wearable
Many watches estimate RHR automatically overnight. That’s usually fine—just make sure the device fits well and the data looks stable.
Threshold Heart Rate (THR): how to estimate it
What it is: A practical intensity marker—roughly the highest effort you can sustain for a “hard but controlled” duration. REN uses THR to anchor zone calculations for “time in zones.”
The REN-friendly rule of thumb
Your threshold heart rate will match approximately with the average heart rate of the 30-minute Critical Speed test.
That means:
If you complete a 30-minute Critical Speed test, the average heart rate from that test is usually a good estimate of your THR.
Tip: Heart rate often ramps up early in hard efforts. If you want to be extra careful, you can also look at the average heart rate over the last 20 minutes—but the full 30-minute average is typically close enough for zone reporting.
Aerobic Threshold (AeT) tests: how heart rate is used (and why these metrics still aren’t required)
For AeT tests, REN looks at heart rate decoupling—the relationship between your pace (or power) and heart rate over time. Decoupling helps indicate whether an effort stays aerobically “steady” or starts to drift as fatigue builds.
Important: To calculate decoupling, REN does not need your resting heart rate, max heart rate, or threshold heart rate.
Decoupling is calculated from the trend between pace and heart rate during the AeT test itself.
REN uses that decoupling result to adjust your AeT paces, keeping your easy/aerobic training appropriately controlled.
So even if you’ve never entered HRmax/RHR/THR, AeT testing and AeT pace adjustments can still work as intended.
What if you don’t know these values?
That’s completely fine.
REN’s workouts are pace-based, so you can train effectively without heart-rate metrics.
Heart rate is used mainly for extra insight in the workout details—especially time spent in zones.
AeT testing uses decoupling, which does not require HRmax, RHR, or THR.
Common reasons heart rate can look “wrong”
If your heart rate seems unusually high or low, it may be caused by:
Heat/humidity
Dehydration
Stress or lack of sleep
Caffeine
Illness
Poor sensor contact (especially wrist sensors)
Cardiac drift during long efforts
This is exactly why REN doesn’t rely on heart rate to drive workouts.
Summary
REN uses HRmax, RHR, and THR to show time in heart-rate zones in workout details.
REN workouts are pace-based, because heart rate can be misleading—especially above ~80% of threshold.
AeT tests use heart rate decoupling to adjust AeT paces, and decoupling does not require HRmax, RHR, or THR.
Not knowing these metrics is absolutely no problem.
Your THR is roughly the average HR of your 30-minute Critical Speed test.