The Navy SEAL Physical Fitness Guide - Uniformed Services ...

Fins and Fin SelectionThere are three factors to keep in mind when you are selecting a fin; the specificdesign characteristics of the fin, the physical attributes particular to your body, andoperational constraints. Fins, by increasing the surface area of the foot, serve to magnifythe thrust delivered by the legs. Kicking with fins involves a forward stroke and a backwardstroke. Several examples will illustrate how the three factors interact to influence theSEAL’s finselection." SDV operations require an operator to sit with fins on for a long period oftime. The operator may require thermal protection and he may have a flexibleankle. Space is limited, so a shorter fin is necessary. For this situation, theoperator should select a short, wide fin with a strap that can be adjusted forvarying amounts of thermal wear." Surface swimming with gear will involve a sidestroke flutterkick. In the sidestroke,forward is toward the front of the swimmer's body and backward istoward the swimmer's back. Applied force is typically much greater duringthe forward stroke, and fins are often designed with this fact in mind. Whenpower is needed for both forward and backward kick, like in sidestroke, astraight symmetrical fin may be more efficient for you." Underwater swimming involves a face down position, where the forwardstroke is down and the backward stroke is up towards the surface of the water.In this position, gravity assists with the downstroke and produces a less symmetricaltype of thrust than seen with sidestroke kick. You should select ahigh-tech diving fin with moderate flexibility and an integral type footbox.The fin should have an offset design to allow a more efficient transfer of propulsionforce." For bodysurfing, use short surf fins.The main principle of fins is to increasethe surface area of the foot.The Navy SEAL Physical Fitness Guide 73