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 pressure response to submaximal exercise | Increase |
| Maximal heart rate | Decrease |
| Resting heart rate | No change |
| Maximal cardiac output, stroke volume | Decrease |
| Endothelial cell reactivity | Decrease |
| Heart rate variability | Decrease |
| Maximal skeletal muscle blood flow | Decrease |
| Capillary density | Decrease |
| Arterial distensibility | Decrease |
| Vascular insulin sensitivity | Decrease |
| Plasma volume, haematocrit | No change, decrease |
| Postural hypotension in response to stressors | Increase |
| Total lung capacity, vital capacity | Decrease |
| Maximal pulmonary flow rates | Decrease |
Table 7.3 Changes in metabolism and body composition due to ageing or disuse, potentially modifiable by physical activity.
| Metabolic/body composition change | Effect of ageing or disuse |
|---|---|
| Resting metabolic rate | Decrease |
| Total energy expenditure | Decrease |
| Thermic effect of meals | Decrease, no change |
| Total body water | Decrease |
| Total body potassium, nitrogen, calcium | Decrease |
| Muscle mass | Decrease |
| Fat mass, visceral fat, intramuscular fat/connective tissue | Increase |
| Bone mass, density, tensile strength | Decrease |
| Protein synthesis rate, amino acid uptake into skeletal muscle, nitrogen retention, protein turnover | Decrease |
| Gastrointestinal transit time | Increase |
| Appetite, energy intake | Decrease, no change |
| Glycogen storage capacity, glycogen synthase, GLUT‐4 transporter protein content and translocation to membrane, oxidative and glycolytic enzyme capacity | Decrease |
| Lipoprotein lipase activity | Decrease |
| Total cholesterol, LDL cholesterol | Increase |
| HDL cholesterol | Decrease, no change |
| Hormonal and sympathetic nervous system response to stress | Increase |
| Growth hormone, IGF‐1a | Decrease |
| Heat and cold tolerance, temperature regulatory ability | Decrease |
LDL, low‐density lipoprotein; HDL, high‐density lipoprotein.
a Most training studies show no change in growth hormone or circulating IGF‐1, although tissue levels of IGF‐1 may increase.
Table 7.4 Changes in the central and peripheral nervous system due to ageing or disuse potentially modifiable by physical activity.
| Function | Effect of ageing or disuse |
|---|