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

Cold water is an issue to be addressed by SEALs training in open water. Althoughthe work of swimming generates heat, there is heat loss created by movement of theswimmer into new “unheated” cold water. Thus, open water swimming may requirevarious combinations of passive thermal protective gear, in particular, wet suits. The threedeterminants for passive thermal protection are:" Temperature" Length of the swim" Effort levelIt is important to remember that wet suits operate by allowing the body heat to betransferred to a layer of water caught between the body and the neoprene material of thesuit. Convective heat loss from the swimmer's body is greatly reduced by this mechanismand as a result, swimming at a high effort while wearing a wet suit allows the swimmer togenerate and retain heat. Guidelines have been developed for training and are presented inthis section.Research has established some known “bench mark” facts about operating in a coldwater environment. In very cold water (below 40° F), the unprotected swimmer loses heatfaster than an immobile person immersed in the same cold water. Heat generation simplydoes not keep up with losses. The immobile person warms the cold water immediatelyaround his body thereby limiting total heat loss. However, in moderately cold water(around 68° F), an elite class swimmer may stay active, and the heat generated byswimming keeps pace with overall losses (although the swimmer may develop cold feetand hands). In this situation, the active swimmer outperforms the immobile person withrespect to maintenance of core body temperature. Currently we do not know the crossovertemperature point or the water temperature at which it is better to remain stationary thanactive in the water for thermal balance.Passive thermal protection modifies this balance by reducing the convectivecomponent of heat loss. As a result, a swimmer may extend training durations beyond thosepossible without passive thermal protection. Diving medicine specialists at BUDS haveThe Navy SEAL Physical Fitness Guide 77