The Relationship Between Coefficients of Drag and Swimming Performance

The purposes of this study were to establish a methodology for measurement of the drag coefficients in swimming and to determine the relationship between the drag coefficients and swimming performance. A new system capable of measuring the hydrodynamic force during swimming in the circulating water channel(CWC). The subjects were ten collegiate swimmers(eight males and two females). The subjects were attached to the load cell and asked to swim the front crawl at the same stroke frequency at different water flow velocities(V). The residual thrust(Tr)which equaled the thrust minus the resintance. The water flow velocity was increased from 0m/s at 0.2m/s intervals until the Tr became negative. Using the relationship between the Tr and the V, the maximum thrust(T0)and the theoretical swimming velocity(T0)were determined by means of regression analysis. The coefficient of active drag(CDa)was calculated by the following equation;CDa=T0/0.5ρ As V20, where ρ represents the density of water and As represents the body surface area. The values of CDa were in the range from 0.038 to 0.085 and tended to decrease with the swimming velocity. There was a significant negative relationship between the CDa and the swimming performance. A lower value of CDa means higher ability to reduce active drag and produce superior performance. We conclude that the CDa is a practical and significant indicator of swimming performance