Mobility Decline in Old Age

Merja Rantakokko; Minna Mänty; Taina Rantanen

Disclosures

Exerc Sport Sci Rev. 2013;41(1):19-25. 

In This Article

Predictors of Mobility Decline

Pain and Obesity as Predictors of Mobility Decline

In the long-term, most chronic conditions along with aging will have a detrimental influence on mobility through various mechanisms influencing the musculoskeletal, neurological, or cardiorespiratory systems. In this section, we discuss two important pathologies predicting mobility loss, namely, pain and obesity.

Musculoskeletal pain is common among older people and is associated with impaired balance and mobility limitations.[12] The pathway from musculoskeletal pain to mobility limitation is not clear. It has been suggested that severe pain in the lower body decreases physical activity that may then lead to a decline in muscle strength and the development of mobility limitations.[33] However, Karttunen et al.[7] found that even after adjusting for potential factors on the pathway, such as self-rated health, depressive symptoms, different chronic conditions, and muscle strength, musculoskeletal pain almost doubled the risk for mobility limitations among older people. Leveille et al.[11] also found that musculoskeletal pain had a direct effect on mobility limitations, independent of the main disablement pathway, via impairments and functional limitation. Presumably, different pathways are present, depending on the underlying cause of pain. For example, hip fracture, a common severe fall-related injury among older people, causes persistent pain in many cases. After hip fracture, along with protracted pain, the muscle strength and power of the fractured leg remain poor. This leads to muscle power asymmetry of the lower extremities and subsequent mobility decline, although the fracture itself has been treated.[22]

Obesity is a rising health problem in both western and nonindustrialized countries. However, the influence of obesity on mobility decline in old age has only recently received more systematic scientific attention. People with excess weight carry a mechanical load, which increases their energy expenditure, placing increased demands on aerobic capacity and muscle strength compared with normal-weight individuals doing similar physical tasks. In a 22-yr follow-up, we observed that people who were overweight in midlife but did not have any impairment approximately had double the risk for future mobility limitation compared with normal-weight people.[35] However, when overweight was accompanied by two or more impairments (poor performance in handgrip strength, squatting test, or self-reported running difficulties) in midlife, the risk for old-age mobility limitation was more than sixfold compared with those with normal body weight in midlife. The increased risk for mobility limitation among obese and overweight people was explained partly by their increased inflammation (C-reactive protein) and low muscle strength, as indicated by handgrip strength in the lowest quartile.[34]

It is possible that some people genetically are more vulnerable to mobility loss and weight gain than others. Twin and family studies provide an opportunity to examine how large a proportion of individual differences are explained by genetic differences. Among monozygotic twins, who share all their genes, phenotypic differences are caused by differences in the environment, that is, behavior, living habits, work, or living conditions. Among dizygotic twins, the genetic resemblance is 50% and, consequently, phenotypic differences between the members of the pair may result from either genetic or environmental differences. We studied a sample of older female twins during a 30-yr period to determine the proportion of genetic factors underlying individual differences in changes in body mass index (BMI) and whether the same genetic factors underlie mobility in old age. We observed that the inverse association between BMI and mobility was explained by shared genes, where genes predisposing people to obesity in middle and old age increased the risk for mobility limitation in later life.[19,20]

Muscle Strength and Sensory Impairments in Mobility Decline

The impairments most commonly studied in relation to walking difficulties are those that directly influence walking, namely, muscle strength and balance. In our early studies, we reported that the maximal isometric muscle strength of handgrip, elbow flexion, knee extension, and trunk flexion and extension correlates with mobility assessed as self-reported difficulties in walking outdoors.[26] The association of mobility and maximal isometric strength also was observed for muscle groups other than those in the lower extremities, as the strength test results showed a within-person correlation. We later reported that the quadriceps strength requirement for a standard stair-mounting task (stepping on a 40-cm-high box) is similar for men and women of different ages.[28] This demonstrates that the reason a larger proportion of 80-yr-old people than 75-yr-old people, and of women than men, was unable to do the task was because of their lower muscle strength. We also reported on quadriceps strength thresholds for walking[27] and identified the minimum required knee extension strength for walking (1.22 m·s−1) and the reserve capacity threshold for the same walking speed. These studies demonstrated that muscle strength is important for the mobility of older people but that the association between muscle strength and mobility is not linear. The strength of the older person needs to be above a certain minimum for performance of the task to be at all possible. Above this minimum, increasing muscle strength improves task performance until the reserve capacity threshold of muscle strength is reached. Above this value, increased muscle strength does not improve task performance as strength no longer limits task performance. The most commonly used measure of muscle strength in large studies is handgrip strength.[31] In a sample of older people, Sallinen et al.[32] determined the thresholds of handgrip strength for the likelihood of mobility limitation, which he defined as difficulty walking 0.5 km or climbing stairs. In cross-sectional data, the overall handgrip strength cut points for the likelihood of mobility limitation were 37 kg (sensitivity, 62%; specificity, 76%) for men and 21 kg (sensitivity, 67%; specificity, 73%) for women. There were differences in the thresholds according to BMI among men. Men with higher BMI had higher cut points; but for women, the cut point did not depend on BMI.

Many studies have focused on the independent effects of various impairments on mobility decline. However, coimpairments, which are multiple impairments simultaneously, may have an even greater impact on mobility decline than the sum of the single impairments involved because people become unable to compensate for one impairment with good capacity in another body system.[29] For example, in a 3-yr prospective study, the likelihood of severe walking limitation (walking speed below 0.4 m·s−1 or unable to walk 400 m) was more than five times greater in the group with balance and strength impairments than in the group with no impairments. Among those who had balance impairment but normal strength, the risk for severe walking disability was threefold. Among those with good balance, strength impairment did not increase the risk for severe walking limitation.[30]

Only limited information exists on the influence of other impairments, for example, sensory impairments, on the mobility of older people. We observed that impairments in sensory functions, such as in vision and hearing, affect mobility decline in older people. Viljanen et al.[37] found in a 3-yr follow-up study that people with hearing impairment had twice the risk for new mobility limitation than people with intact hearing. Auditory information may be more important for safe outdoor mobility than traditionally considered. For example, hearing loss may hinder the ability to divide attention between traffic, discussion, maintaining postural balance, and walking, thus potentially increasing the risk for falls and other accidents. Sensory impairments may accelerate the process of mobility decline by restricting participation in out-of-home activities.

Kulmala et al.[8] found that people with coexisting vision and hearing impairments had more than fourfold risk and people with coexisting impairments in vision, hearing, and balance had almost 30-fold risk for falls compared with people with no vision impairment.

Falling and Its Consequences for Mobility

Falling and fall-related injuries are common among older people, often leading to a sudden and catastrophic disability. Approximately 20% to 40% of community-dwelling individuals older than 65 yr fall every year, and about one half of those who fall repeatedly do so.[21] Known individual risk factors for falls include higher age and health-related issues such as gait problems, muscle weakness, dizziness, and other disease-related conditions. In addition, environmental factors play a major role in falls.[21] Irrespective of related serious injuries, whether falls have a negative impact on mobility among older people has been little investigated in prospective studies. We suggest that falls also may lead to progressive mobility decline in the absence of consequent injury. In our study, older women with indoor falls were more than three times more likely to report new difficulties in walking 2 km by the end of the 3-yr follow-up compared with those with no falls (Table 1). Outdoor falls did not increase the risk for future mobility limitation.[16] A significant proportion of the increased risk for mobility decline among those who sustained at least one indoor fall was caused by their higher baseline obesity, lower walking activity, and higher prevalence of chronic conditions. Among women who sustained indoor falls, were obese, and reported low walking activity, the risk for incident mobility limitation was 17-fold compared with women with none of the risk factors.[16]

Preclinical Mobility Limitation

There is great variability in the progression of mobility limitations among older people. For some, it may be sudden and catastrophic; whereas for others, it may be slowly progressive.[5] Sudden onset of mobility limitation usually is a result of a traumatic event, such as an injurious fall; whereas a slow progressive decline in mobility is a consequence of worsening health conditions, such as arthritis.[5] If the decline in mobility slowly progresses, then in the early stages, before the onset of task difficulty, older people may be able to compensate for underlying impairments or physiological decrements by modifying their performance and thus maintain their everyday function without (any) strong perception of difficulty.[1] For example, a person may reduce his or her walking pace or use a mobility aid to manage a certain walking distance, without perceiving any difficulty in doing so. This early stage of mobility decline has been termed preclinical mobility limitation and refers to a stage between good mobility and manifest mobility limitation[3,4,14] (Fig. 1).

Figure 1.

Process of mobility decline; preclinical mobility limitation (gray shaded box) is an early stage of mobility decline and refers to a stage between good mobility and manifest mobility limitation. (Reprinted from [13]. Copyright © 2007 Elsevier. Used with permission.)

Preclinical mobility limitation may be assessed by asking people who do not report task difficulty whether they have changed their way of doing the task.[3,4,14] Our study showed that self-reported preclinical mobility limitation was associated with a decline in measured physical performance and that it was highly predictive of further mobility decline.[14] Older adults who reported baseline preclinical mobility limitation had up to sixfold higher risk of progressing to major manifest mobility limitation during a 2-yr follow-up compared with participants with no limitation at baseline (Table 2).[14] Furthermore, our 12-month prospective fall surveillance suggested that preclinical mobility limitation combined with a fall history predicted future falls.[15] These results, together with previous evidence by Fried et al.,[3,4] indicate that self-reported preclinical mobility limitation is a useful measure for early identification of people at high risk for mobility decline, thereby offering an opportunity for early intervention.

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