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, syndromes for which there is no pharmacological therapy.4,19 Dementia/cognitive decline is another emerging epidemic without a pharmacologic cure in which treatment of mild cognitive impairment with robust exercise is effective compared to gentle stretching and toning exercise. Importantly, cognitive gains are proportional to strength improvements.4,24 highlighting the need for prescriptions that are concordant with potential anabolic pathways beneficial for both neural and muscular function. Therefore, it is vital to promote healthy and dignified ageing by helping healthcare systems more efficiently implement evidence‐based programmes for frail older adults in all community and aged care settings.
Inter‐individual variability in response to exercise (non‐responder phenomenon)
Dose‐response relationships between changes in fitness and better health outcomes have been defined for some, but certainly not all, diseases and syndromes. Some modalities or doses of exercise promoted for older adults (mild callisthenics, slow‐paced walking) have little or no discernible effects on physical fitness but may yield benefits in some domains. This area of investigation is critical for defining threshold and optimal levels of activity that are necessary for health promotion and disease management. It should be recognised that what is suitable for prevention may be entirely inadequate for treatment, as is also the case with pharmacological management of chronic diseases. For example, aspirin may reduce the risk of ischaemic heart disease, but a host of potent agents and surgery may be required once coronary occlusive disease is present and symptomatic.
Dose‐response heterogeneity is not unique to pharmaceutical therapies.25 In the era of precision medicine, interindividual variability in the magnitude of response to supervised exercise training (subject‐by‐training interaction or individual response) has received increasing scientific interest in both adults and children.26‐31 For instance, some individuals show improvements with exercise training (e.g., decrease in fasting glucose) and are considered responders, whereas others may not have such a response (e.g., no change or even increases in fasting glucose) and are considered non‐responders.32 A physiological non‐response to exercise in one outcome does not signify a non‐response in all outcomes. Exercise and medical researchers have recognised the substantial variability in patient response to physical exercise interventions and have sought to understand these differences. Individual interaction of physiological, molecular (i.e., genetics, epigenetics, transcriptomics, and metabolic factors), and environmental factors are being investigated as potential mediators of the lack of a response to exercise in some participants.33
Does exercise increase life expectancy?
The effects of exercise on total mortality are unlikely ever to be substantiated via randomised controlled clinical trials, given the impossibility of random assignment to various physical activity regimens over many decades. However, there is clear evidence of an inverse, linear dose‐response relationship between the volume of physical activity reported in epidemiological
