Critical Speed Calculator
Fit critical speed and D′ from two or three time trials.
Method and limitations
Ordinary least squares fits distance = criticalSpeed × time + D′. Distances and times must be finite and positive; all trial durations must differ. Nonpositive critical speed and negative D′ are rejected. D′ is the distance intercept, not an independently measured energy store.
Use separate, comparable maximal efforts with appropriate recovery. Three trials provide more information than two. Two points fit exactly by construction; R² = 1 does not validate the model. Residuals are displayed. Predictions are limited to interpolation within the time span of the entered trials. No unrestricted marathon extrapolation or universal evidence-based trial-duration cutoff is claimed.
Internal calculations retain full precision; only displayed results are rounded. Empty inputs are not treated as zero. General software limits are 1,000 km, seven days and at most 500 split rows; model-specific limits are stated above. These are responsiveness limits, not validated athletic ranges.
Distance/time conversions use the exact international mile (1609.344 m). Run/walk, interval, split and track results are arithmetic pacing plans, not independently validated ability predictions.