Converging indicators for assessing individual differences in adaptation to extreme environments.

It is well known that microgravity results in various physiological alterations, for example, head-ward fluid shifts which can impede physiological adaptation. Other factors that may affect crew operational efficiency include disruption of sleep-wake cycles, high workload, isolation, confinement, stress, and fatigue. From an operational perspective, it is difficult to predict which individuals will be most or least affected in this unique environment given that most astronauts are first-time flyers. During future lunar and Mars missions space crews will include both men and women of multi-national origins, different professional backgrounds, and various states of physical condition. Therefore, new methods or technologies are needed to monitor and predict astronaut performance and health, and to evaluate the effects of various countermeasures on crew during long-duration missions. Herein we describe the development and validation of a new methodology for assessing the deleterious effects of spaceflight on crew health and performance. We reviewed several studies conducted in both laboratory and operational environments with men and women ranging in age between 18 to 50 yr. The studies included the following: soldiers performing command and control functions during mobile operations in enclosed armored vehicles; subjects participating in laboratory tests of an anti-motion sickness medication; subjects exposed to chronic hypergravity aboard a centrifuge; and subject responses to 36-h of sleep deprivation. Physiological measurements, performance metrics, and subjective self-reports were collected in each study. The results demonstrate that multivariate converging indicators provide a significantly more reliable method for assessing environmental effects on performance and health than any single indicator.