Connect Your Strava Account

Connect your Strava account to analyze your running data and calculate your Critical Speed.

CS & D' Progress Over Time (12 Months)

Monthly data points • 6-week rolling windows

Analyzing your training progress...

Heads up: Your most recent fitness estimate is more than 6 weeks old. Run a few quality efforts (one short, one long) to get a fresh CS reading.
CS & D' Progress Over Time
Latest CS
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Latest D'
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CS Trend
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D' Trend
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Insufficient Data: You need at least 3 activities in a 6-week window for analysis. Connect more Strava data or try the Custom Analysis tab below.

Critical Speed Analysis

Calculating your Critical Speed...

CRITICAL SPEED
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D' (D-PRIME)
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D' Depletion Calculator

Enter a target pace to find out how long you can sustain it before your anaerobic reserve (D') is fully depleted. Only works for paces faster than Critical Speed.

All three models estimate CS from the same data using different mathematical approaches. Hyperbolic (highlighted) is the gold standard in exercise science research and is used as your primary result. If the models disagree substantially, try adding shorter efforts (<5 min) to your selection.
Durability Analysis — CS at Different Time Ranges
Time Range Critical Speed (m/s) Critical Speed (min/km) CS Drop (%) Interpretation
Shows how Critical Speed changes when calculated using data up to different time durations. Greater CS drop indicates poorer durability at longer time ranges.
Durability Analysis — Critical Speed Models
Comparison of Critical Speed models calculated using different time ranges. Click legend items to show/hide specific models.
What do these numbers mean?

Critical Speed (CS): The highest sustainable speed you can maintain theoretically indefinitely.

D' (D-prime): Your finite capacity for work above Critical Speed before fatigue.

R²: How well the model fits your data (closer to 1.0 is better).

Test Analysis

Try the analysis with sample data while you set up Strava integration.

Your Running Activities

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