Critical Swim Speed (CSS) represents the maximum pace a swimmer can sustain aerobically over an extended effort. It’s calculated from the difference between 400m and 200m best times: CSS = (400-200) ÷ (400m time - 200m time) in seconds per metre, then scaled to seconds per 100m. CSS-based training zones (used by the Swim Smooth coaching system) structure training from easy recovery (120%+ of CSS) through threshold work (at CSS) to race-pace and sprint intervals.
Key points
- (400-200)m ÷ (T400-T200) = CSS
- Swim equivalent of FTP
- Foundation of Swim Smooth zone system
- Training at CSS is highly effective for improvement
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