1. The Physiological and Psychological Environment in Humans

It seems to be in the human nature to pursue the extreme while being exposed to extreme environments with sometimes little a priori knowledge about the prevailing conditions. Extreme environments, whether occurring naturally or artificially, are subject to extreme physical forces. These conditions are responsible for triggering specific physiological alterations in the human body to maintain physiological functionality and to ensure survival. The process of physiological maintenance and adaptation can be described from the perspective of homeostasis, allostasis as well as psychological resilience. Each of these terms are mechanisms that regulate a human’s physiology and psychology to enhance health, wellness, performance, and survival. Thus, this chapter explores the boundaries of human capabilities and introduces the fundamental concepts and underlying mechanisms of physiological and psychological responses to extreme environment exposure. These concepts apply uniformly to any kind of environmental stimuli and can be translated and specified for physiological and psychological system responses. Different application scenarios are further explored in the following chapters in the book.