Balance and Mobility

The ability to stand and walk, often taken for granted, is necessary for full independence in daily activities and integration in society. Balance and mobility often decline with aging, and specific diseases also lead to deficits. The contracted living space, need for care, falls, and injuries that result from this decline are important sources of illness in older persons, are costly to society, and are important determinants of caregiver burden and even the need for nursing home placement.

Normal walking involves propelling one's body forward as one's feet catch up and prevent a fall. Walking is, therefore, inherently unstable. A foot strikes heel-first, then rocks forward, with the toe the last part to leave the ground. Gait is divided into a stance phase, when both feet are on the ground, and a swing phase, when one foot is off the ground. Stride length is the distance from the heel strike of a particular foot to the next heel strike of that foot.

Investigation of aging-related changes in mobility was largely initiated in the late 1960s by Dr. Patricia Murray, a kinesiologist at the Medical School of Wisconsin. She found that older adults had slower walking speeds, shorter stride lengths, longer stance phases, and less foot clearance off the ground. Older adults also have less arm swing and a trunk that is bent slightly forward. Figure 1 displays these differences. Some investigators have found that older adults have an irregular cadence (step frequency).

Balance requires contributions from several systems: motor, sensory, and cognitive. Muscles, typically lower limb or hip, contract to maintain balance. Older adults may have weaker muscles, delayed reaction times, coactivation (so that muscles with opposite actions contract together, thereby stiffening a joint), and disorganized muscle contraction (so that muscle groups are not working together). The sensory system is also important. Vision, the vestibular system of the inner ear, and proprioceptive nerves (those which detect the position of joints and muscles) are all important in balance, and can all become less functional with age. Cognition also contributes, because attention, which can decline with age, is important in maintaining balance. The balance system is redundant, in that deficits in one system can be compensated for by the other systems. The changes mentioned above can occur with aging and also with specific diseases.

Transfers must also be considered. "Transferring" is the term used for moving from one condition to another, such as out of a bathtub, chair, or car, or getting into bed. The ability to transfer depends on many factors, including strength, balance, vision, and flexibility. The characteristics of the transfer surface and the presence or absence of adaptive aids can have an impact on transfer ability.

Figure 1 Limb position differences between older (left) and younger (right) men at the moment of heel strike. SOURCE: Murray et al. Journal of Gerontology. (1969): 176

These changes with aging are averages, and not all older adults age at the same rate. A group of eighty-year-olds will have a much wider range of abilities than a group of twenty-year-olds. Some of the eighty-year-olds will have abilities that are indistinguishable from those of the average twenty-year-old, while others will be totally dependent. Heterogeneity of abilities is a characteristic of older age.

Mobility also requires energy, and so blood circulation and oxygenation must be adequate to meet the body's needs. Any impairment in heart, lung, or blood vessel function will impair mobility.

The effects of mobility deficits associated with aging or disease can often be minimized through the use of walking aids, such as canes or walkers. These aids are just that—tools that help older adults maintain their independence— though many seniors view them as restrictive signs of aging and are reluctant to use them. Similarly, a wheelchair can provide freedom and independence to someone who might otherwise be bedbound or housebound.

The role of the environment in mobility should not be forgotten. For example, it is more difficult to get out of a very low chair or one without arms. A very soft bed makes it harder to roll over. Given the multiple components of balance, a darkened room will have a negative impact.