measures adequately mirror the diverse challenges and functions of many occupations.
Physiological and metabolic tests also may not adequately reflect cognitive, adaptive skills that come with experience and extensive training, to meet job challenges and changes.
As noted above, in many instances it may not be possible to distinguish the various causes of laboratory-measured decrements in function. Candidate causes of these changes include genetic forces, modifiable environmental exposures, and nascent clinical illnesses or disorders; the implications for maintaining worker health and functions are very different for each of these factors.
Although maximum capacity to function may be important in certain instances, most occupations do not usually require performance at full individual capacity. Thus, workplace or other exposures may cause decrements in function from full capacity without affecting work performance or function at usual levels. At the level of national economies this is particularly true since there has been a decline in the proportion of physically demanding blue-collar jobs in many industrialized countries. Conversely, there has been an increase in cognitively demanding occupations.
Age-related decrements in bodily physiological functions may be related to the duration as well as the number and intensity of symptoms and acute responses to physiological work stresses that almost all persons experience. That is, functional decrements may relate to temporary symptoms and conditions that alleviate over time but may be more common among older workers. For example, certain stereotypic work activities may lead to painful muscles and joints, which are not different among older or younger persons in their onset but may take longer to dissipate in older workers. Similarly, common upper respiratory infections may have longer courses among older persons, including older workers. Age-related decrements may be related to the permanent performance decrements, but only to varied persistence of temporary acute stresses.
Despite the cautions and conceptual issues noted above, there is substantial data on organ system-specific physiological and functional changes with age. While the various causal and contributing factors are uncertain, they are likely to include environmental exposures (including those in the workplace); genetic factors; positive and negative health behaviors; as well as medical and preventive services. The following is a brief overview of important age-related changes in organ systems that are possibly important to job exposures among older workers and the job experience: