REN workouts are built around pace targets, not heart rate or running power. Pace is the most direct, practical way to execute running workouts consistently—especially when your training plan is based on thresholds and race-specific speeds.
Why not heart rate?
Heart rate can be useful for easy running and general monitoring, but it becomes too volatile for precise workout targets—especially above your Aerobic Threshold (AeT).
On harder sessions, heart rate can swing a lot due to:
fatigue and recovery status (“form of the day”)
heat, humidity, and dehydration
stress, sleep, caffeine, and fueling
cardiac drift during longer efforts
That means you can end up “chasing” a heart-rate number that doesn’t match the intended training stimulus.
Why not running power?
Running power is an indirect measure and can vary significantly between devices, algorithms, and conditions. While it can be interesting, we currently consider it less accurate and less consistent than pace as a primary target for REN workouts.
Pace isn’t perfect either (and we account for that)
Pace is influenced by:
terrain and surface
gradient (hills)
wind and weather
That’s exactly why REN uses target ranges (not one exact pace) and why we ask you to use RPE (how it feels) during your runs.
We don’t expect you to execute workouts like a robot. The goal is to hit the right effort and training effect, even when conditions aren’t perfect.