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      ³ Saint Louis University School of Medicine, St Louis, Missouri, USA

Introduction

      The interaction of physical activity, exercise, and physical fitness with health and ageing is complex and multifaceted. Although many questions remain about mechanisms of effect and optimal modalities, a synthesis of the literature indicates many positive effects of participation in physical activity on the ageing process and mortality, with dose‐response curves indicating benefits are linked to both intensities and volumes of exercise. All recent position stands and policy recommendations¹ include exercise prescriptions for health promotion and disease prevention and treatment in older adults, including cardiovascular disease, diabetes, arthritis, renal failure, depression, emphysema, peripheral vascular disease, stroke, and Parkinson’s disease, among others. There is strong evidence that exercise training is an effective intervention for improving muscle strength, muscle mass, bone density, incidence of falls, and mobility in older adults across the health status and frailty spectrum.¹ Exercise also has an emerging role in preventing and treating cognitive decline and dementia, with specific robust forms of exercise such as high‐intensity resistance training most promising, particularly in those with mild cognitive impairment.^2‐4 In addition, multicomponent exercise intervention programmes, including resistance, balance, and mobility training, are an effective strategy for improving the hallmarks of frailty (low body mass, strength, mobility, physical activity level, energy) and thus optimising functional capacity during ageing.⁵ Based on the association between muscle power output and physical function, and the very dramatic loss of muscle power specifically with ageing (due to fast‐twitch fibre atrophy and changes in neural recruitment), there is a rationale for a central role for explosive resistance training (known as power training) in the exercise prescription whenever possible to optimise functional outcomes in both fit and frail older adults.⁶

      Exercise has not become fully integrated into usual geriatric medicine practice and is still virtually absent from the core training of most geriatricians and other healthcare professionals. Therefore, this chapter attempts to provide a rationale for using exercise and physical activity for health promotion and disease prevention and treatment in older adults. Exercise is discussed in terms of the specific modalities and doses that have been studied in randomised controlled trials for their role in the physiological changes of ageing, disease prevention, and treatment of older people with chronic disease and disability. Recommendations will be offered to address gaps in knowledge and also clinical implementation needs in this field.

What is physical activity or exercise?

      Any discussion of these issues must begin with definitions of terminology.⁷ Physical activity has traditionally been defined as any bodily movement produced by contraction of skeletal muscle that significantly increases energy expenditure, although the intensity and duration can vary substantially. This activity may be performed during leisure or occupational hours, and surveys of older adult should capture both paid and unpaid (volunteer) work. Exercise is a subcategory of leisure‐time physical activity in which planned, structured, repetitive bodily movements are performed, with or without the explicit intent of improving one or more components of physical fitness: aerobic capacity, muscle strength power and endurance, balance, coordination, and flexibility.

Recently, efforts have been focused on merging these formerly distinct entities of structured exercise and physical activity to promote ‘lifestyle integration’ of exercise as a means to enhance long‐term adherence. For example, taking the stairs instead of the elevator, standing on one leg while doing the dishes, or slowly standing and sitting without use of the arms represent ways of incorporating aerobic, balance, and strengthening exercises, respectively, into everyday activities. Current investigations are exploring whether such prescriptive techniques are superior to standard approaches for promoting behavioural change and targeted clinical outcomes such as falls in older adults, for which there is some support in the literature.⁸

      Physical fitness, by contrast to the behaviours defined above, is defined as a set of attributes that contribute to the ability to perform physical work (e.g., cardiorespiratory endurance, muscle function, balance, flexibility, and body composition) or influence health status. Metabolic fitness has been advanced more recently as a term that encompasses a range of biologically important traits (increased insulin sensitivity, lipoprotein lipase activity, endothelial cell reactivity, heart rate variability, etc.) that may contribute to health status but do not directly affect exercise capacity. Both genetic predisposition and lifestyle factors contribute to physical and metabolic fitness and the extent to which they are modifiable with exercise training.

Physical inactivity versus exercise

      The World Health Organization’s ‘Global Recommendations on Physical Activity for Health’ state that adults 65 and older should engage in 150 minutes of moderate‐ or 75 minutes of vigorous‐intensity aerobic activity and 2 or more days of muscle‐strengthening activity (i.e., strength/resistance training)^9,10 each week. The US Department of Health and Human Services (HHS) suggests that multicomponent exercise training of at least moderate intensity that is performed 3 or more times per week for a duration of 30 to 45 minutes per session over at least 3 to 5 months appears most effective to increase functional ability in frail older people.¹ The World Health Organization (WHO) has recognised that lack of physical activity is a major risk factor for morbidity and premature mortality.¹¹ Indeed, estimates from 2012 indicate that not meeting physical activity recommendations is responsible for more than 5 million deaths globally each year.¹² Recently, data from more than 1 million individuals indicate that high levels of physical activity, equivalent to 60–75 minutes of moderate intensity physical activity per day, seem to eliminate the increased mortality risks associated with high total sitting time.¹³ However, current PA guidelines are often not met, particularly in older adults. For example, in the 2015 Behavioural Risk Factor Surveillance Survey of 383,928 adults in the US age 18–80, only 17.8% of adults 65–74 and 15.4% over 75 reported meeting both aerobic and resistance exercise guidelines (defined as moderate‐vigorous aerobic activity ≥ 150 minutes/week and resistance training ≥ 2 sessions/week).¹⁴

      Physical inactivity is a key factor contributing to the onset of muscle mass and function decline (i.e., sarcopenia),¹⁵ which in turn appears to be a vital contributant to frailty.^4,16,17 Deterioration in muscular strength and mass, cardiovascular resistance, and balance lead to a decrease in daily life activities, higher risk of falling, and loss of independence, among other consequences. Many of the chronic diseases associated with ageing are also related to the superimposed negative effects of excess sedentary behaviour and insufficient exercise. Across the lifespan, the diseases affected by insufficient physical activity include coronary artery disease, obesity, type 2 diabetes, several cancers, osteoarthritis, chronic lung diseases, neurological diseases, and mental health conditions, among others.^18,19 The evidence now clearly shows that being physically active and having a healthy diet (coupled with a lack of smoking and moderate alcohol consumption) are integral to maintaining health and well‐being at all ages.^19,20

      The effects of exercise and a healthy lifestyle are similar to those that can be achieved with medication when aiming to prevent cardiovascular disease, diabetes, and obesity; improve muscular function and quality of life; and reduce risk of mortality.^21,22 Importantly, the syndromes for which we have no safe or effective pharmacological treatment (e.g., cognitive decline and dementia, falls, sarcopenia, frailty, disability) are the areas for which exercise has been shown to be of particular benefit. Notably, even when we have medications that can be used, exercise may be preferable due to its better risk/benefit ratio. For example, it is a potent and more effective substitute for psychotropic medications used for depression, anxiety, and insomnia in older adults, with their well‐known risk of falls and hip fractures.²³ Multi‐component physical exercise programmes that include robust resistance training and balance training are the most effective interventions for delaying disability and reducing falls,

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