Compensatory Strategies Used by Older Adults Facing Mobility Disability

Do We Know Enough About Preclinical Disability? 

As developed and implemented, preclinical disability is a method for identifying precursors to disability through ascertainment of compensatory strategies when disability is not yet present. Thus, the approach offers a preventive framework and the opportunity for early intervention. For many daily tasks, there are alternative ways of getting things done. A compensatory strategy can be defined as a way of achieving a result that is adopted frequently in the face of a physical impairment or limitation and under usual conditions. Compensatory strategies are also usually recognizable as something healthy people do not “normally” do. As an example, most people do not use a cane to walk. At one time, canes were used often as a fashion statement. Now, they are used to compensate for an activity limitation related to walking. Under demanding conditions, such as climbing across jagged boulders, even the healthiest person would appreciate a cane; in contrast, on a flat, nonslippery surface, a cane be recognized as a compensatory strategy. General categories of compensation for mobility include behavioral adaptations, using technology or environmental supports, and receiving human help.18, 19 Gignac et al20 applied the Baltes’s theory of selective optimization with compensation to mobility disability, classifying a wide range of adaptations. By using their scheme, preclinical disability encompasses a range of adaptations, including “selection” by performing the activity less often, “optimization” by planning activities to avoid problems, “compensation” by using assistive devices, and “receiving help.”

Approaching preclinical disability at this conceptual level leads to consideration of the complexity of the issue; preclinical disability has a dual nature with compensation as both a risk marker associated with impairment or limitation and a mediating risk factor affecting the natural history of disability. A large amount of potential heterogeneity among such compensations remains to be understood. Most importantly, perhaps, are the qualitative differences between strategies that leverage abilities to overcome threats to activity and participation in life and strategies that consist of decreasing task demands. Does a compensatory strategy lead to less or more activity? Some gerontologists believe that people on the chronic pathway to disability should “use it or lose it!” Is relying on someone’s arm for support when walking fearful walking, and does it lead to using one’s own physiologic systems for balance less and walking less? Or, does it lead to overcoming barriers and walking more? Thus, there are many worthy future research questions regarding mobility compensations, some of which will require advanced methods because of compensations’ complex, nonindependent, nature. Why does someone start to compensate? What are the downstream effects of spontaneous compensations? What are the tradeoffs between different compensatory strategies? Can distinct contributions from diseases, changes in energy utilization and metabolism, psychologic factors, and environmental and social variables as causes of compensation and disability be identified? How do these factors affect the gradual transition from preclinical disability to overt disability? The interaction between the individual and his/her environment is an emphasis of the new World Health Organization conceptual model of disability1 and a research area that will surely lead to theoretical and practical insights into how to apply more potent therapeutic strategies. Nonetheless, we propose that enough is known already about preclinical disability to move forward to translational research and clinical application.

Should We Be Screening? 

To chart directions about the way forward in applying knowledge about preclinical disabilities in clinical settings to improve the health of older adults, a review of the 4 criteria for screening provides a useful structure.

Is the Outcome a Significant (Prevalent and Potent) Public Health Burden? 

Should the outcome be rare enough, even a near-perfect screening test can be more likely to lead to a false-positive than a true-positive. In this case, mobility disability is a huge public health burden, with a prevalence on the order of 30% to 50% in adults 65 years and older.21 Furthermore, the prevalence of preclinical disabilities in mobility tasks is considerable, ranging from approximately 20% to 40% in prior studies and 31% to 55% in the sample of adults age over 75 reported by Mänty et al7 in this issue.

Is There an Acceptable Level of Potential Harm? 

Some screening tests lead to dangerous procedures or treatments and serious psychologic burden. These concerns are mitigated if the consequence of screening is tailored recommendations for physical activity, as in this case. Low risk from resulting interventions lowers the bar for screening. Although we should not minimize the need to carefully monitor for adverse effects in trials of physical activity in older adults, the level of concern about potential harm is arguably acceptable in this case.

Can a Treatable Preclinical Phase Be Identified Accurately? 

This screening criterion is poorly suited to preclinical disability because mobility disability is a latent construct with no criterion standard. However, the epidemiologic studies of predictive validity mentioned previously form a reasonable basis for moving forward. In addition, nomograms are available, providing screening accuracy data for clinical use.17 Perhaps ironically, a challenge to establishing the accuracy of measures of preclinical disability lies in the fact that many older adults experience fluctuations in health status. For example, the risk of disability among women with preclinical disability has been found to be 26% to 31% at 18 months, depending on the item measured. The likelihood of improvement or recovery to reporting no preclinical disability was 31% to 34%.13 Similarly, substantial rates of recovery have been found for disability. If some would get better on their own, should we be intervening? Several considerations are relevant. Periods of transient disability followed by recovery form one of the strongest risk factors for recurrent and persistent disability.22, 23 We do not yet know who will spontaneously recover or if such recovery will be optimal. Furthermore, increasing physical activity as an intervention leads to multiple benefits across a range of physiologic systems and dimensions of health, beyond benefits in mobility, forming the basis of a strong argument for tailored activity interventions in the presence of preclinical disability.

Is Early Intervention More Effective Than Waiting for Overt Presentation? 

There may be sufficient data to move toward effectiveness trials targeting preclinical disability. In a trial of prehabilitation, a home-based intervention was found to benefit older adults who were able to perform an out-and-back 10-foot walk test in less than 10 seconds or able to rise from a chair with arms folded. Notably, the intervention was not effective in those who were unable to do both.24 In a study by Mann et al,25 home visits by an occupational therapist providing assistive technology and environmental modifications to increase function and safety reduced the rate of functional decline. There are other examples, both from epidemiologic studies and interventions, suggesting that restorative therapy alone may miss opportunities to prevent disability. Preclinical disability aims to identify people in a transitional zone, functionally, who are not already near the benefit ceiling from an intervention, yet not so sick that recovery to a previous state of functioning is much less likely to occur.

The Benefit Will Be Large 

In the Women’s Health and Aging Study II, the probability of becoming disabled in women with preclinical disability was 26% to 31% at 18 months versus 7% to 12% in those with no preclinical disability.13 The risk difference between these groups was therefore 14% to 24%. An intervention with the modest expectation of altering this outcome in 1 in 4 people would be associated with an absolute risk reduction of one fourth of 14% to 24% or 3.5% to 6%. The corresponding number needed to treat (NNT) is 17 to 29. By comparison, the NNT with a statin to prevent a generous composite measure of death or a nonfatal stroke or heart attack is estimated to be 35.26 These rough calculations provide some perspective on the potential for clinical benefit from treating preclinical disability. However, these figures do not consider that only small proportions of the population are either very active or very physically disabled, and the vast majority fall closer to the middle and are more likely to benefit from an intervention than those at the extremes. As is the case in treating blood pressure, focusing public health efforts on middle values (blood pressures in the low-abnormal or even high-normal range) would lead to massive population benefits because that is where most of the population lies. Similarly, effective efforts to treat preclinical disability in older adults will have a large impact on the health of our aging population.

Who Can Respond to This Challenge? 

PM&R and geriatric medicine offer complementary and overlapping expertise important to the treatment of physical disability in later life. Physiatrists are trained in the mechanistic treatment of impairments and limitations, focused primarily on restorative therapy or tertiary prevention, especially after an acute illness or injury, and are comfortable with the empirical nature of prescribing and adjusting therapeutic regimens to maximize activity for a patient. Geriatricians bring knowledge gained from identifying and intervening on multifactorial syndromes and age-related diseases that interact to create nonspecific clinical presentations, such as fatigue, and lead to aggregate outcomes such as disability, experience in the prevention of disability and in prioritizing among many possible medical treatments, and skill minimizing adverse reactions to medical treatment. The geriatricians’ focus is often on primary and secondary prevention. Collaboration between rehabilitation and geriatrics experts now tends to occur only during acute rehabilitation. Extending this collaboration to other settings is needed to make even larger gains in population health. More than ever, collaborative clinical and research efforts joining PM&R and geriatric medicine are likely to make contributions that, in the context of a demographic imperative to ameliorate health in later life, will lead to large public benefit.