Active and Passive Fatigue States

Transportation systems are expected to work around the clock. From transcontinental flight and interstate trucking to container ships and railroads, contemporary society demands nonstop operations. However, there is one component of all transport systems that is not made for continuous activity — the human operator. The conflict of inherent human limitations with our contemporary "24-hour" society leads to a pervasive problem—fatigue. Fatigue represents a most insidious condition because, being personal, it is often hard to identify unequivocally and therefore difficult to measure and thus regulate. This chapter outlines a new model of fatigue that makes a critical distinction between two forms of fatigue state: "passive" and "active" fatigue. In the experimental record on fatigue and common task performance, most studies have examined perceptual-motor capability involved for prolonged periods. Active fatigue is then derived from continuous and prolonged, task-related perceptual-motor adjustment. In contrast is a second form of fatigue, passive fatigue, which requires system monitoring with either rare or even no overt perceptual-motor response requirements. Closely allied with vigilance, this form of fatigue develops over a number of hours of doing what appears to be nothing at all.