Measurement of the active drag coefficient in front-crawl: A stroke-by-stroke analysis

The purpose of this study was to understand the change in active drag coefficient (C_DA) over successive stroke cycles in front-crawl and the relationship between swimming speed and C_DA. Eighteen national competitive swimmers (nine girls and nine boys with a mean age of 14.91 ± 0.59 years) were recruited. Swimming speed, propulsion (F_total) and frontal surface area were measured to calculate the C_DA. Swimming speed (F = 1.790, p = 0.182, η² = 0.07) and C_DA (F = 0.907, p = 0.413, η² = 0.06) did not change significantly over time, but swimming speed showed a decrease between the second and third stroke cycle. On the other hand, the F_total changed significantly over time (F = 4.437, p = 0.019, η² = 0.21). Swimming speed and C_DA showed a linear and strong relationship (R² = 63.8 %). A stroke-by-stroke analysis showed that national level swimmers were able to maintain their hydrodynamic profile during a front-crawl maximal trial. Thus, it can be argued that a decrease in swimming speed can be related to a decrease in F_total. Swimming speed and C_DA showed an inverse and significant relationship, with lower values of C_DA resulting in faster swimming speeds.