To deal with such conceptual complexities, research regarding aging and working life has increasingly made use of a theoretical orientation commonly termed the life course perspective (Riley and Riley, 1994; Marshall and Mueller, 2002; Markson and Hollis-Sawyer, 2000). According to this flexible model, while social institutions and public policy structure the life course into stages that most individuals move through, the connection is a loose coupling (Elder and O’Rand, 1995). Individual workers—based on their particular circumstances—can have a much more varied and disorderly life course than that assumed by the traditional three-stage model (Rindfuss, Swicegood, and Rosenfeld, 1987). Instead of marching predictably through uniform life stages, individual members of an age cohort will move in and out of the workforce in a variety of ways at a variety of age points. Their transitions are still socially patterned, but some patterns depart considerably from the normative model. Assessing the available research literature, Marshall and Mueller (2002) note that departures from the normative working life trajectory are particularly common among segments of the population that are not white, middle class, or male.

Rather than concentrating on “the aged” as a chronologically defined category, the life course perspective treats aging as a process that unfolds throughout life, reflecting each individual’s social context and cumulative experiences. The orienting principles emphasize the importance of individual biography, specific historical events and social conditions experienced by the individual, the network of relationships an individual has, the timing of specific events in a person’s life, and the choices that people make within the opportunities and constraints of history and social circumstances (Riley, 1979; Elder, 1994, 1997; Elder and Johnson, in press).

Figure 1-1 shows a simplified, schematic representation of how a life course perspective informs the understanding of how environmental exposures relate to age-related health changes and clinical outcomes. The abscissa represents increasing age; the ordinate represents the functional status of the body’s organs. The three lines sloping downward represent alternative pathways in the function (e.g., physiology and metabolism) of an organ or organ system. This model assumes that there are a variety of environmental and occupational exposures of varying intensity and pathogenicity both early and late in life. The dashed horizontal line represents a threshold below which clinical organ dysfunction (e.g., disease) is apparent. The upper curve represents the optimal scenario for age-related change, in which environmental exposures are minimized and health promotion and disease prevention are maximized. The middle curve represents usual aging, population averages summarizing varied environmental and occupational exposures and preventive applications in the workplace and elsewhere. The

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