CSS from 400 m + 200 m

Two maximal swims in the pool. Critical swim speed (CSS) comes from the difference between distance and time of the two efforts.

Protocol

Swim 400 m and 200 m, each at maximal effort (ideally in the same session, with adequate recovery between them). Select the pool type (25 m short course, 50 m long course, or yards) and record the time of each swim.

Formula

speed = (400 − 200) / (t400 − t200) [m/s]

pace/100 = 100 / speed

About the source

The concept of critical swim speed (CSS) as a swimming performance index comes directly from Wakayoshi et al. (1992), with additional validation in 1993 showing that CSS approximates maximal lactate steady-state intensity — a direct scientific origin, with no coaching intermediation.