ranging from fewer than 500 to over 2.5 million individuals) and all‐cause mortality rates.1 These relationships are demonstrable for both men and women and for both older and younger adults. Volumes of energy expenditure during exercise of at least 1000 kcal per week reduce mortality by about 30%, whereas reductions of 50% or more are seen with volumes closer to 2000 kcal per week, when more precise measures or estimates of physical activity participation incorporating fitness assessments are utilised instead of surveys. These changes in all‐cause and cardiovascular mortality translate to an increase in life expectancy of ~2 years for those exercising at such volumes. In a recent example, in a cohort study of 16,741 women with a mean age of 72, women who averaged approximately 4400 steps/day had significantly lower mortality rates during a follow‐up of 4.3 years compared with the least active women who took approximately 2700 steps/day. More steps taken per day were associated with lower mortality rates until approximately 7500 steps/day.34
Despite the consistency of the data from well‐designed observational studies, many questions remain regarding the minimum threshold for efficacy; the effect of exercise intensity, duration, and frequency (apart from contributions to overall volume); the effect of non‐aerobic modalities of exercise; and the mechanisms of benefit. From a public health perspective, if small, effective doses of moderate‐intensity activity are found to be as beneficial as longer bouts of vigorous activity, adoption of mortality‐reducing physical activity recommendations by sedentary middle‐aged and older adults may be more successful. Of particular relevance to the exercise prescription for this cohort are studies that have demonstrated that a change from a sedentary to a more active lifestyle in midlife or beyond is associated with a reduction in mortality. In the sections that follow, the focus is on changes in functional capacity, physical fitness and body composition, quality of life, and disease burden, rather than on changes in longevity itself. It is in these domains that the centrality of physical activity patterns to optimal ageing is perhaps most relevant to the concerns of the healthcare professional and the older individual.
Physical function as a biomarker of healthy ageing and objective of exercise programmes
Physical function (i.e., characteristics such as aerobic capacity, gait speed, balance, mobility, and muscle strength) is currently being proposed as a biomarker of healthy ageing in humans, predictive of adverse health events, disability, and mortality, in addition to tools commonly used as functional outcomes for clinical trials.35 Recently, Ramirez‐Vélez et al.36 showed that older adults with handgrip strength greater than the muscle weakness thresholds had lower odds of adverse events in most of the intrinsic capacity domains, as well as a lower hospitalisation rate (in men) than their weaker peers, adjusted for disease burden. Thus, multi‐morbidity, including cardiovascular disease, is not the most important factor modulating individual domains of intrinsic capacity (i.e., cognition and mental health, sensory function, metabolic rate, mobility, and muscle strength) responsible for functional decline and diminished ability to perform activities of daily living (ADLs). Moreover, physical performance measures, such as gait speed, predict mortality in older adults better than chronic diseases (e.g., hypertension), and preservation of functional capacity is now a primary focus for clinicians in the management of cardiovascular diseases, for example.37,38 For these reasons, functional ability‐ retaining autonomy and independence as people age‐ is the cornerstone of healthy ageing, a term established by the WHO in its first world report on ageing and health.39
From a clinical point of view, frailty has emerged as one of the most relevant clinical syndromes in geriatric medicine. This term relates to a distinctive ageing‐related health state in which multiple body systems gradually lose their in‐built capacity, resulting in decreased physiological reserves and resilience in the face of stressors.40,41 Over the last few years, it has attracted increasing interest due to its direct relationship with adverse health effects such as physical and functional decline, institutionalisation,42,43 disability, hospitalisation, poor quality of life, excess morbidity, and increased mortality.44 Accordingly, an important conceptual idea for frailty is that the focus should be on functionality rather than the diagnosis of disease for older patients. Thus, improving or maintaining function becomes the ultimate mission for the medical care of older people. In addition, it has been shown that the best strategy is to prevent functional decline instead of trying to recover function once it has been lost.5,45
Preserving exercise capacity with age via an active lifestyle
There is a great similarity between the physiological changes attributable to disuse and those typically observed in ageing populations, leading to the speculation that the way we age may be modulated with attention to activity levels.46 As previously stated,19 the detrimental effects of exercise removal (such as enforced bed rest) on these physiological systems can be compared to the symptomatology presented by patients with diagnosed frailty. As the benefits of exercise affect a broad range of physiology, exercise deficiency will affect systems traditionally thought of as being exercise‐dependent and also more remote systems, mimicking the mosaic of presenting symptoms in frailty. With continued lack of physical activity, additional systems failures are inevitable as the toxic mix of inactivity and factors such as poor diet, pain, depressive symptoms, cognitive dysfunction, and fatigue negatively impact and distort the trajectory of the inherent ageing process. The parallels that exist between frailty and exercise deficiency can be seen in the unpredictable presentations and variation of symptomology that can occur. Because of the tenuous links between the value of a physiological function and a specific age, it can be predicted that the degree of exercise deficiency in each individual, rather than their chronological age, will be better correlated to clinical outcomes. Similarly, because of the inherent heterogeneity, the length of time an individual has been sedentary may not correlate with severity of symptoms.19 The most important physiological changes associated with ageing or disuse that impact exercise capacity are presented in Tables 7.1–7.4. In most physiological systems, the normal ageing processes do not result in significant impairment or dysfunction in the absence of other pathology and under resting conditions. However, in response to a stressor or prolonged and profound disuse, the age‐related reduction in physiological reserves (homeostenosis) may result in difficulty completing a task requiring near‐maximum effort. This could be as ‘simple’ a task as rising from a chair, which may exceed the hip and knee extensor strength of a frail octogenarian, for example.
Table 7.1 Changes in exercise capacity due to ageing or disuse, potentially modifiable by physical activity.
| Component of exercise capacity | Effect of ageing or disuse |
|---|---|
| Maximal/peak aerobic capacity | Decrease |
| Tissue elasticity | Decrease |
| Muscle strength, power, endurance, coordination | Decrease |
| Oxidative and glycolytic enzyme capacity, mitochondrial volume density | Decrease |
| Gait speed, step length, cadence, gait stability | Decrease |
| Static and dynamic balance | Decrease |
Table 7.2 Changes in cardiorespiratory function due to ageing or disuse, potentially modifiable by physical activity.
| Cardiorespiratory function | Effect of ageing or disuse |
|---|---|
|
Heart rate and blood
|
