The Effect of Stroke Length on Active Drag in Swimming

The main resistive force in swimming is due to drag on a swimmer’s body from the water. There are two forms of drag, one is active drag (FD), which is the drag encountered while propelling the body through the water. The other is passive drag or the drag encountered while gliding during a push-off after a turn or after entering the water from the start. These different types of drag are both proportional to the frontal area (the projected area that is perpendicular to the direction of travel) and approximately proportional to the square of the swimmer’s velocity (Clarys, 1978). Minimizing the frontal area of the body in the water can reduce drag and is achieved both by streamlining and by increasing buoyancy in the water (such that more of the body is out of the water and/or the body is positioned more horizontally) (Kolmogorov et al., 1997). It was also determined that the best swimmers have been able to find a way to minimize active drag. Others have found low passive drag to be a good predictor of performance (Chatard et al., 1990).