Deconditioning can be defined as the multiple, potentially reversible changes in body systems brought about by physical inactivity and disuse. Such changes often have significant functional and clinical consequences in older people. Deconditioning commonly occurs in two situations: (1) a sedentary lifestyle, which is common in older people even in the absence of significant disease or disability and may result in a slow, chronic decline in physical fitness; and (2) bed or chair rest during an acute illness, which can lead to disastrously rapid physical decline.
Decline in muscle strength and muscle bulk is the most important and consistent feature of deconditioning. Reduced maximal oxygen uptake during exercise, impairment of balance responses, and decreased cardiac output during exercise have also been linked to deconditioning but may primarily result from the reduction in muscle bulk.
Aging or deconditioning?
Many people, and even some health care professionals, often see much of the disease and loss of function found with aging as a normal and inevitable consequence of aging. However, it is now clear that such changes are in fact due to a combination of true age-related decline, disease (whether overt or hidden), and disuse. It is often difficult in practice to determine the relative contribution of each of these factors.
Muscle mass declines steadily with increasing age. This results in a loss of muscle strength of 1 to 2 percent per year. It is important to note, however, that reduced muscle mass (or sarcopenia ) with age cannot be entirely due to inactivity, as it is also found in highly trained elderly athletes. The patterns of muscle loss do appear to differ between the two. While aging results in a reduced number of muscle fibres, disuse primarily causes a reduction in muscle fibre size. Sustained muscular activity requires the delivery of an adequate supply of oxygen to the muscles and utilization of the oxygen in the mitochondria of the muscle cells. Cross-sectional studies (comparing people of different ages) and longitudinal studies (serial examinations of people as they age) have found a decline in maximal oxygen uptake with age. The most important factor in this decline may be the changes in muscle mass due to either age or disuse, since maximal oxygen uptake is almost independent of age when expressed relative to fat-free mass (mass mainly composed of muscle). Similarly, cardiac output shows little change with age when related to fat-free mass.
The degree to which decreased physical activity with increasing age is a cause, rather than an effect, of reduced muscle bulk is uncertain. Jackson and colleagues have argued that about half of the decline in exercise capacity over the adult life span can be attributed to chronic physical inactivity and the resultant changes in body composition (increased body fat and reduced muscle bulk). The beneficial effects of exercise training programs on muscle strength, exercise capacity, and balance suggest, but do not prove, that the decline in physical fitness with old age is at least partially preventable.
Effects of acute illness
Major trauma, sepsis, or surgery lead to the breakdown of skeletal muscle in order to provide nitrogen and amino acids essential to immune function and tissue repair. While this response can be ultimately beneficial, the resultant loss of muscle mass and strength may impede recovery of normal function after surgery. This is particularly likely if breakdown of muscle is compounded by unnecessary immobilization (as often happens in a hospital) or if prior deconditioning has led to preexisting muscle weakness and a smaller reserve of muscle for consumption.
Functional consequences of deconditioning
Muscle strength of itself matters little; what is important is how changes in muscle strength affects the ability to perform daily activities. As the strength of a muscle decreases with age, activities relying on that muscle require a greater proportion of the maximum strength of the muscle. Eventually, a threshold is reached where the maximum strength available to an individual for a particular action is the minimum strength required for that action. Any further decline in muscle strength will make the activity impossible. If that activity is essential to an independent existence, a small decline in muscle function, such as following a brief period of inactivity due to acute illness, may be sufficient to cause dependence. For example, the quadriceps (thigh muscle) is the most important muscle used in rising unaided from a toilet or from a low chair. The threshold for quadriceps contraction needed to perform these activities is reached at about the age of eighty in women, and a few years later in men.
Appropriate patterns of muscle contractions in the leg (and trunk) are used to adjust and maintain balance (following a stumble, for instance). Deconditioning can adversely affect balance in a number of ways. Disuse atrophy will reduce the functional reserve of muscles needed to maintain balance. For example, loss of strength in the muscles that flex the ankle joint (dorsiflexors) has been associated with falls in nursing-home residents. Prolonged bed rest may cause the brain to adapt to the recumbent position and hence lead to imbalance when the patient eventually tries to walk.
Risk factors for deconditioning
The cumulative effects of multiple chronic diseases such as dementia, depression, stroke, osteoarthritis, heart failure, incontinence, respiratory disease, and diabetes mellitus contribute to physical inactivity and disability in older people. Inadequate dietary intake and nutritional deficiencies exacerbate age-related decline in muscle mass. Psychosocial factors—such as the attitudes of older people themselves, and of caregivers and relatives—are also important. For example, an attitude that physical decline is inevitable in old age can lead to a delay in seeking medical attention for treatable problems. The end result is a reduction in functional reserve, which increases the risk of clinically significant decline during intercurrent acute illness. People with increased susceptibility to disability and deconditioning are often described as frail.
Acute illness in older people is often complicated by development of acute confusion (delirium), incontinence, immobility, or instability. Indeed, these may be the presenting features of acute illness—myocardial infarction may present with confusion rather than chest pain. An atypical presentation may result in delayed presentation by the patient and delayed diagnosis and treatment by the doctor and is a predictor of a poor outcome.
Hospitalization of older people may have deleterious effects distinct from the effects of acute illness. The unusual environment and routine of hospitals and complications of polypharmacy and of therapeutic and diagnostic procedures may worsen or precipitate problems like confusion or incontinence. Use of urinary catheters in incontinent patients or treatment of delirium with physical restraints or with sedative medications will exacerbate immobility and functional impairment. Functional dependency may be reinforced if hospital staff are overly concerned about the risk of falls or if they perform, rather than supervise, daily activities. In addition, social networks may disappear during a long illness, and patients may become demoralized and depressed.
Prevention and treatment of deconditioning
The adage "use it or lose it" is true at all ages, but it is a fundamental tenet of the care of older people. Given the difficulties of reversing deconditioning and its functional effects once established, prevention is the best option. This requires a variety of strategies.
Regular physical exercise in middle age protects against many conditions common in old age, including late-onset diabetes mellitus, osteoporosis, hypertension, and cardiac disease. The role of exercise in older life in combating these conditions is less clear. However, Roy Shephard has noted that physical training can lead to the equivalent of a twenty to thirty year reversal of the usual age-associated decline in aerobic power. Maintenance of physical fitness and avoidance of a sedentary lifestyle with increasing age must therefore be an important goal of community health programs, reinforced whenever possible by advice from doctors to individual patients. In particular, patients and caregivers must be educated about the importance of maintaining physical activity even in the face of significant chronic illness, as well as the importance of early intervention during acute decline or illness.
Prevention of deconditioning in hospitals during acute illness requires a multifaceted approach that includes physical therapy, maintenance of nutrition, medical management, and psychological support. Activity and independence should be promoted from the time of admission. Education of health care staff about the dangers of deconditioning is vital, since bed rest continues to be recommended during acute illness despite the lack of evidence showing benefits and the considerable evidence showing potential adverse effects from this advice. Sedative medications and restraints should be used sparingly, if at all.
Exercise programs can be beneficial for older people regardless of their disability. In randomized controlled trials of both healthy and frail elderly subjects, including people over eighty years of age, exercise has been shown to improve lower-limb muscle strength, exercise endurance, balance, speed of walking, and overall levels of physical activity. Practice of specific skills is required if improved muscle strength is to translate into functional benefits. Exercises including a balance component (e.g., tai chi) may be useful in preventing falls. Physical exertion has potential dangers, and exercise programs for older people should be tailored to the needs and capacity of the individual person.
Restoration of physical function and independence in a frail and deconditioned hospital patient is particularly difficult. Comprehensive clinical, functional, and psychosocial assessment is mandatory. It is important to set measurable, attainable goals and to monitor progress carefully. This is aided by the use of standardized tools to measure important areas such as cognitive function and the ability to perform daily activities. An active multidisciplinary rehabilitation program is essential, and should include nutritional and psychologic support.
See also Exercise; Frailty; Geriatric Medicine; Physiological Changes; Physiological Changes, Organ Systems: Skeletal Muscle; Surgery in Elderly People.
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