summarize. For young adults, mobility limitations such as those caused by spinal cord injuries, orthopedic impairments, and paralysis are the most common causes. For middle-aged and older adults, chronic diseases, especially heart and circulatory problems, predominate as causes of limitation. Figure 1 shows the age-specific prevalence rates for activity limitation according to five groups of causes; Figure 2 shows the proportion in each age group ascribed to each of the groups of conditions.
Modern medicine's success in averting the death of many people who sustain life-threatening diseases and injuries often entails, as a consequence, the loss of at least some functional capacity. Indeed, the successful lifesaving techniques of modern medicine are adding to the population of people with disabilities. For example, in the 1950s, only people with low-level paraplegia were generally expected to survive; today, even people with high-level quadriplegia are surviving and living lives of high quality. Indeed, one commentator has characterized the growing numbers of people with chronic conditions as the ''failures of successes" achieved with medical technology. To help these individuals restore functional capacity, avert further deterioration in functioning, and maintain or improve their quality