The main objective of this study was to confirm that the passive drag coefficient is less dependent on swimming
speed than the passive drag, Froude, and Reynolds numbers, even as swimming speed increases. The sample consisted of
12 young proficient non-competitive swimmers (seven males and five females: 20.4 ± 1.9 years). Passive drag was
measured with a low-voltage isokinetic engine at 1.2, 1.4, 1.6 and 1.8 m/s. The frontal surface area was measured using
digital photogrammetry. Passive drag showed significant differences with a strong effect size over the four towing speeds
measured (F = 116.84, p < 0.001, η2 = 0.91) with a quadratic relationship with speed. The Froude and Reynolds numbers
had similar trends, but with linear relationships. Conversely, the passive drag coefficient showed non-significant
differences across the four towing speeds (F = 3.50, p = 0.062, η2 = 0.33). This strongly suggests that the passive drag
coefficient should be the variable of choice for monitoring the hydrodynamic profile of swimmers rather than the absolute
value of passive drag.
