REF-932 · Dekerle et al., 2005 · International Journal of Sports Medicine, Vol. · Paper · PubMed

Critical Swimming Speed Does not Represent the Speed at Maximal Lactate Steady State

Blimited evidenceMeasured on highly trained athletesWritten before October 2026, being re-checked

Critical swimming speed (CSS) is a mathematical construct: in theory, a speed that could be held indefinitely — but what it means physiologically in swimming was still unsettled. Here CSS was set against a directly measured speed at maximal lactate steady state (S MLSS).

Eight swimmers, all well trained, did four exhaustive swims, from whose distance-time relationship CSS was derived, plus four sub-maximal 30-min swims at constant intensity to locate S MLSS. CSS came out significantly faster than S MLSS, and the two agreed too loosely to be swapped for each other, even though they were strongly correlated.

The authors conclude that in swimming CSS is not the highest speed that can be sustained before blood lactate starts to climb continuously.

Participants

n=8 well-trained swimmers, aged 18.6 +/- 1.9 years; MEDLINE indexing lists male participants.

Protocol

CSS: four tests to exhaustion at 95, 100, 105, and 110 % of maximal aerobic speed (MAS); CSS from the distance-time relationship.
S MLSS: found from four sub-maximal 30-min swims at constant intensity, set between 75 % and 90 % MAS.
Agreement assessed by bias +/- 95 % limits of agreement and by correlation.

Key Results

MeasureValue
CSS92.7 +/- 2.6 % MAS
S MLSS88.3 +/- 2.9 % of MAS
Bias +/- 95 % limits of agreement (CSS vs S MLSS)0.07 +/- 0.13 m x s(-1)
Correlationr = 0.87; SEE = 0.033 m x s(-1); p < 0.01
CSS was significantly higher than S MLSS; the disagreement was "too great to use these two variables interchangeably".

Practical Application

In eight well-trained swimmers, CSS (92.7 % of maximal aerobic speed) was significantly higher than the directly measured speed at maximal lactate steady state (88.3 %), with a bias of 0.07 m/s; the two were strongly correlated (r = 0.87) but not interchangeable. To "can I hold CSS pace indefinitely / is CSS my lactate threshold?": no — at CSS blood lactate keeps rising, so treat it as a hard threshold-and-above pace for repeats, not as a steady long-swim pace.
CSS still ranks swimmers the way the lactate steady state does (strong correlation), so it remains a usable anchor for zones; it is the meaning of the number that changes.
Inference, not tested here: continuous aerobic swims and long race legs belong several percent of pace below CSS; the abstract gives the gap in % of maximal aerobic speed for these swimmers, not a transferable pace offset.
Not from this paper; the base's own practice: the swim framework SYNTH-74 anchors swim paces to a tested CSS; the same "the mathematical threshold sits above the lactate steady state" relation is described for critical power in REF-168.

Limitations

Eight well-trained young male swimmers; no triathletes, masters or women.
CSS from four exhaustive tests near maximal aerobic speed, not the two-distance pool test athletes use; the size of the gap may differ with the test.
MLSS located from four 30-min tests, so its resolution is limited by the spacing of the tested speeds.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

test validation / method comparison, n=8