Critical Speed vs Threshold Pace: Key Differences Explained
Compare critical speed and lactate threshold: how they differ, when they diverge, and which metric to use for training and racing.
Quick Answer
Critical speed (CS) is a model-derived boundary from time-trial data. Lactate threshold (LT) is a metabolic event measured by blood lactate response. They often align near 30-60 minute race pace, but they answer different questions and can diverge in individual runners.
When they agree
For well-trained runners on flat courses, CS and LT2 pace are often within 5-15 seconds per mile. Both approximate the intensity you could hold for roughly one hour.
Side-by-Side Comparison
| Factor | Critical speed | Lactate threshold |
|---|---|---|
| Definition | Model-based speed-duration boundary | Blood lactate inflection point |
| How measured | 2-3 time trials or races | Lab test, 30-min TT, or race estimate |
| Equipment needed | Watch and known course | Lactate meter (lab) or HR monitor (field) |
| Also provides | D' (anaerobic reserve) | LT1 and LT2 zones |
| Best for | Race pacing models, interval design | Tempo training, HR zones |
When CS and LT Diverge
High D' runners
Runners with strong anaerobic capacity may have CS slightly below LT pace because short time trials overestimate sustainable speed. They excel at 5K but fade earlier than CS predicts at marathon pace.
High-mileage endurance runners
Marathon specialists may have LT pace closer to half-marathon effort while CS sits nearer 10K pace. Their aerobic efficiency extends sustainable duration beyond what short trials suggest.
Testing conditions
Heat, hills, or poor pacing in time trials skew CS. LT lab tests in cool conditions may not match outdoor race CS estimates.
Workout Implications
| Workout type | CS-based target | LT-based target |
|---|---|---|
| Tempo run | 95-100% CS | LT2 pace (T pace) |
| VO2max intervals | 105-120% CS | 3K-5K race pace |
| Easy run | 65-80% CS | Below LT1 |
| Marathon pace | 80-88% CS | Between LT1 and LT2 |
Which Should You Use?
Use lactate threshold for tempo workouts and heart-rate zone training. Use critical speed for modeling race performance across distances and designing intervals that account for anaerobic depletion. Many coaches use both: LT for day-to-day zones, CS for race strategy.
Calculate both metrics from your recent race results and compare.
Editorial references
- Critical power and locomotor exercise
Poole, D.C. et al. (2016). European Journal of Applied Physiology.
- Lactate threshold concepts and training implications
Faude, O., Kindermann, W., & Meyer, T. (2009). Sports Medicine, 39(6), 469-490.
- Jones, A.M. et al. (2019). The maximal metabolic steady state in running. Sports Medicine, 49(7), 1019-1035.