How often should CSS be retested?

Every 4 to 6 weeks to evaluate aerobic fitness improvements and recalibrate workout interval split targets.

Updated: August 2026 • Verified v1.2

Critical Swim Speed (CSS) & Aerobic Training Zones Calculator

Health & Daily LifeNew

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CSS (m/s) = (400 - 200) / (T400 - T200); CSS_Pace = 100 / CSS_mps; D' = 400 - (CSS * T400)

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Understanding Your Results

Calculates critical velocity in meters per second, CSS base pace per 100m, anaerobic work capacity (D' in meters), predicted 1500m threshold times, and generates a 5-tier training zone chart with split pace offsets.

Practical Guidance & Next Steps

Critical Swim Speed represents the threshold pace a swimmer can sustain for 30-40 minutes without continuous blood lactate accumulation. Doing 100m repeats at CSS with short 10-15s rest is the gold standard for aerobic endurance.

What is this?

A sports physiology utility that calculates an athlete's Critical Swim Speed (CSS) and prescribes customized aerobic training zones.

How does it work?

1. Enter 400m and 200m all-out swim time trial results. 2. View Critical Velocity in m/s, CSS base pace per 100m, and anaerobic capacity (D'). 3. Review prescribed 100m target split times for Recovery, Endurance, Threshold, and Sprint zones.

Why use it?

Enables swimmers and triathletes to train at scientifically validated aerobic paces rather than guessing workout intensity.

Technical Scope & Calculation Limitations

Ginn & Wakayoshi two-point critical velocity model.

Frequently Asked Questions

CSS is the swimming equivalent of Functional Threshold Power (FTP) in cycling—the maximum swimming pace you can maintain aerobically without fatiguing exponentially.

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