Swimming zones from CSS
Critical Swim Speed (CSS) = your best sustainable aerobic pace. Estimate from your 400m and 200m times.
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Frequently asked questions
What is Critical Swim Speed?
CSS is the fastest pace you can sustain aerobically over a long swim. It's the swim equivalent of FTP in cycling or lactate threshold in running. Training at CSS pace is highly effective for improving swim fitness.
How do I improve my CSS?
Threshold sets (CSS pace efforts of 400-1500m total volume) are the most effective. Red Mist sets (CSS pace with short rests) and pace-specific work build the physiological capacity to sustain faster swimming aerobically.