Critical Speed (CS) is one of the most important thresholds in running. It’s the pace you can sustain for about 30 minutes at maximum effort. REN uses this value to individualize your training intensities and help predict race performances.
How REN Determines Your Critical Speed
From Personal Bests
REN can estimate your CS pace using your previously logged race or time trial results (5K, 10K, etc.).With a Critical Speed Test
You can perform a dedicated test:Warm up properly (light jogging, mobility drills, a few strides).
Run 30 minutes all-out — as hard as you can sustain for the full duration.
Your average pace during those 30 minutes is your Critical Speed.
Other Names for Critical Speed
Critical Speed is sometimes called:
Threshold Pace
Anaerobic Threshold Pace
All these terms describe a similar concept — the fastest pace you can hold without quickly accumulating fatigue.
Why REN Prefers “Critical Speed”
Clear Definition
“Threshold” can mean different things in different training systems (lactate threshold, ventilatory threshold, anaerobic threshold, etc.). CS has a simple, measurable definition: 30 minutes all-out pace.Easy to Test
You don’t need lab equipment or blood lactate tests. A stopwatch, a track, or GPS is enough.Directly Useful
CS connects directly to real training and racing — it’s the anchor point between endurance paces (slower than CS) and high-intensity paces (faster than CS).Personalized Training
Because it’s based on your own performance, CS ensures all workout zones (endurance, threshold, VO₂max) are scaled to your ability.
✅ In short: Critical Speed is your personal 30-minute max pace. REN uses it as a cornerstone of your training plan because it’s easy to measure, practical to apply, and directly linked to how you perform in races.