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Fitness

Critical Swim Speed

Critical swim speed (CSS) estimates the pace you could hold for about thirty minutes—derived from timed 400 and 200 swims or similar tests. Coaches use CSS to set aerobic threshold intervals and send-off times.

Critical swim speed (CSS) estimates the pace you could hold for about thirty minutes—derived from timed 400 and 200 swims or similar tests. Coaches use CSS to set aerobic threshold intervals and send-off times.

Retest every four to six weeks as fitness changes.

Common questions

  • How do I test critical swim speed?

    After a warm-up, swim a 400 and 200 time trial with adequate rest between; plug times into a CSS calculator or coach formula for threshold pace per 100.

  • How often should CSS be retested?

    Every four to six weeks in a build phase, or after a taper block, so interval paces match current fitness instead of outdated numbers.

Related guide

Building a Sustainable Fitness Routine: Evidence-Based Strategies →

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