Speedo Speed Swim Training Fins The short convex blade curvature and pass through vents promote optimum speed and unlike other training fins on the market allow for a six beat kick The blade curvature and ridges create more pressure on the up kick creating balanced propulsion and muscle work load. This is the ideal fin for freestyle, backstroke and butterfly training. Lightweight and pliable foot bed material provides ideal fit and comfort. Open heal design offers greater ankle flexibility and comfort.