The Positive Drive Fins (PDF's) use a unique ellipsoidal blade to generate correct propulsion in all four swim strokes. The asymmetrical blade design allows the swimmer to build power while promoting a natural inward supination kick style for butterfly, backstroke and freestyle. The PDF's use an ergonomic foot pocket to comfortably place feet in an ideal swimming position. The heel strap secures the fin, allowing feet to flex more naturally. A closed toe design provides superior energy transfer from leg to foot. The PDF's will increase leg strength, foot speed and ankle flexibility for all four swim strokes, making the fins great for individual medley training.