Abstract
Modern society has placed several stressors in our lives, and with an increase in global conflict, military personnel live in a constant state of alert. This has been further complicated by urban warfare and terrorism threats, leading to a level of constant stress, sleep fragmentation, and sleep deprivation. In the combat zone, military personnel are required to maintain their vigilance around the clock in order to deal with adverse situations, which can lead to sleep deprivation and cause cognitive impairment and, in turn, increases the risk for the safety of their company and themselves. This chapter addresses sleep and fatigue and their tolls on the physical and cognitive function of military personnel as well as countermeasures to fatigue.