Throughout the world all populations are seeing burgeoning numbers of “elders”, defined as persons aged 65 year and older. In many countries, including Japan, the United States, Norway, Sweden and the United Kingdom, those aged over 65 are at or approaching 15% of the population. As their numbers have increased, so have their health care expenses, leading to extensive research on the health, well being, and life expectancy of these increasingly older elders. Today this group is further sub-divided: the young-old ages 65–74, the old-old ages 75–84, and the oldest-old ages 85+, for both health care and research purposes. However broad variation still characterizes even these groupings. Rates of frailty and disability increase with increasing age among these elders. For example, inabilities to complete at least one activity of daily living increased from about 5–7% at ages 65–69 years to about 28–36% at ages 85+ in 1987. Death rates continue to decline at all ages past 50 years and rates of disability seem to be doing the same. For the foreseeable future, we may expect increasing numbers of older, frail elders than in previous decades. Thus, people are not only living longer, they generally are healthier at advanced ages than were previous cohorts, thus “old age” disabilities of the 20th century will be put off to even older ages during the 21st century. As yet there is no clear way to assess senescent changes in humans, although activities of daily living, allostatic load, and frailty indices have all been suggested. One future need is greater development and use of universal and accessible design in all aspects of the built environment.

Before developing agriculture, herding or metallurgy, humans occupied most of the world. Multiple socioculturally-based responses supported their migration, including building shelters and constructing niches to limit environmental stressors. Sheltered settings provided social support and security during stressful times, along with opportunities for injured, aging, and frail members to survive. Modern built environments are designed for similar purposes, to support human growth, development, reproduction, and maintenance. However, extended survival in modern settings has costs. With age, muscle (sarcopenia) and bone loss (osteopenia, osteoporosis), along with somatic, physiological, and sensory dysfunction, reduce our physical capabilities, increase our frailty, and impede our abilities to interface with built and natural environments and manufactured artifacts. Thereby, increasing our dependence on built environments to maintain autonomy and quality of life.What follows is a conceptual review of how frailty may limit seniors within modern built environments. It suggests age-related frailty among seniors provides specific data for those designing environments for accessibility to all users. It is based in human ecological theory, and physiological and gerontological research showing senescent alterations, including losses of muscle, bone, and sensory perceptions, produce a frail phenotype with increasing age limiting our mobility, activity, use of space, and physical abilities. As an individual phenotype, frailty leads to age-related physical and performance declines. As a physiological assessment, frailty indices amalgamate individual measures of functional abilities into a single score. Such frailty indices increase with age and differ betwixt individuals and across groups. To design built environments that improve access, usability, and safety for aging and frail citizens, today’s seniors provide living samples and evidence for determining their future abilities, limitations, and design needs. Designing built environments to accommodate and improve the quality of human-environment interactions for frail seniors will improve usability and accessibility for most user groups.

Over the past century there has been a large and continuing increase in the frequency of persons aged over 65 years; particularly those aged over 100 years. During the 21st century the number of persons over 100 years will continue to increase. This will occur at such a rapid rate that the 21st century may one day be called the century of centenarians. Frailty and disability secondary to senescence, disease, and trauma have accompanied old age (often defined as age 65 and over) as far back as recorded history. However, during the 20th century, age, frailty, disability, and chronic degenerative diseases have been decoupled to some extant in the most long-lived human populations. Until recently, there was little need to design artificial environments for the unique needs of the elderly due to their low representation in most national populations. Today that need is increasing in concert with the number of persons aged 65 and older. The purpose of this review is to suggest areas wherein physiological anthropologists may have an opportunity to contribute to design trends for this rapidly increasing aging population. Major considerations for design of environments for the elderly are based upon altering the environment to accommodate their declining visual, auditory, and kinesthetic senses, thereby enhancing their declining faculties and improving their autonomy, independence, and self perceptions of well-being. To date most design considerations have been directed toward improving environments for those suffering from Alzheimer's disease or residing within assisted living facilities. Many such design improvements also may be effective in improving life satisfaction and functional abilities of the non-institutionalized elderly.

All over the world people are surviving into their seventh and later decades of life more frequently today than ever before in human history. Some remain in good health, while others show chronic degenerative conditions (CDCs), frailty, and relatively rapid mortality. Thereafter, multiple factors promoting health and well-being become ever more complex as we age. After attainment of reproductive maturation, many physiological decrements occurring in concert with age reflect both senescent and disease processes, not simply the passage of time. Senescence is a process that begins with DNA, molecules and cells and ultimately terminates in cellular death, loss of organ function, and somatic frailty. These changes are different from benign changes with age that do not alter function. Both differ from the pathological processes represented by disease. Either disease or senescence may be age-related, but neither is age-determined. Disease results from pathological alterations and it affects all age groups. Diseases need not be related to senescence, which includes alterations due to inherent aspects of organismal biology. Distinctions among senescence, aging, and disease blur for the late-life CDCs because, in addition to disease processes, many CDCs are phenotypic manifestations of senescing DNA, organelles, cells, and organs. During earlier epochs of human evolution, greater environmental exposures and fewer cultural buffers likely lead to greater frailty and mortality before senescence progressed greatly, as they still do for most animals. In modern-day settings, culturally patterned behaviors have allowed human frailty to become disconnected somewhat from mortality, unlike non-human species.