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Training Tips

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    How to Use the Critical Swim Speed (CSS) Calculator

    The CSS Calculator determines the pace you can theoretically maintain indefinitely, ideal for setting training zones and improving endurance. Here’s how to use it:

    Calculating CSS

    Enter times and distances for two time trials (e.g., 200m and 400m). The calculator computes your CSS pace and training zones.

    Example: 200m in 2:30, 400m in 5:15 → CSS ≈ 1:22.5/100m.

    Unit Selection

    Choose between meters and yards. The calculator adjusts calculations and provides pace metrics in your chosen unit.

    Use your CSS to structure endurance training. Learn more about pacing with USA Swimming’s Tips for Pacing and Technique.

    CSS Calculation Formulas

    Understand the math behind Critical Swim Speed:

    CSS Formula

    CSS (sec/100) = (Distance₂ – Distance₁) ÷ (Time₂ – Time₁) × 100

    Calculates the pace per 100 meters/yards you can sustain aerobically.

    Speed Calculation

    Speed (m/s) = 100 ÷ CSS (sec/100m)
    Speed (km/h) = Speed (m/s) × 3.6
    Speed (mph) = Speed (m/s) × 2.237

    Training Zones

    Zone Pace = CSS × Percentage (e.g., 105% for Easy, 90% for Threshold)

    Adjusts CSS pace for different training intensities.

    Unit Conversions

    1 meter = 1.094 yards
    1 yard = 0.914 meters

    Applied when switching between metric and imperial units.

    Frequently Asked Questions

    What is Critical Swim Speed (CSS)?
    CSS is the pace you can theoretically maintain indefinitely without exhaustion, representing your aerobic threshold.
    How do I improve my CSS?
    Focus on aerobic endurance with interval sets at or near CSS pace, combined with technique work to reduce drag.
    What distances should I use for CSS?
    Typically, 200m and 400m time trials are used, but other pairs like 100m/200m or 400m/800m can work if times are accurate.
    How often should I test CSS?
    Test every 6-8 weeks during consistent training to track aerobic improvements.
    Does CSS differ in pool vs. open water?
    Pool CSS is typically faster due to controlled conditions and push-offs. Open water CSS may be slower due to currents and navigation.