exercise
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 |
|---|---|
| REM and slow‐wave sleep duration, sleep efficiency | Decrease |
| Cognitive processing speed, accuracy | Decrease, no change |
| Attention span | Decrease, no change |
| Memory | No change, decrease |
| Executive function | Decrease, no change |
| Motor coordination, force control | Decrease |
| Neural reaction time, neural recruitment | Decrease |
| Autonomic nervous system function | Decrease |
REM, rapid eye movement.
Although changes in absolute work capacity (aerobic fitness or maximal oxygen consumption) are immediately noticeable and disastrous for an elite athlete, they may accrue insidiously in non‐athletic populations because most sedentary individuals rarely call upon themselves to exert maximum effort in daily life. Women are particularly susceptible here because their initial reserve of muscle mass is so much lower than that of men, owing to gender differences in the anabolic hormonal milieu and also lifestyle/occupational factors. Therefore, they cross the threshold where losses of musculoskeletal capacity (sarcopenia) impact frailty/functional status at least 10 years before men do on average.
Another important consequence of age‐related changes in physiological capacity is the increased perception of effort associated with submaximal work (a lowering of the anaerobic threshold or the approximate level at which significant dyspnoea occurs). This changing physical capacity has the unfortunate negative side effect of increasing the tendency to avoid stressful activity. Such behavioural change compounds the sedentariness caused by changing job requirements or retirement, societal roles and expectations, and other psychosocial influences. Thus, a vicious cycle is set up: ‘usual’ ageing leading to decreasing exercise capacity, resulting in an elevated perception of effort, subsequently causing avoidance of activity, and finally feeding back to exacerbation of the age‐related declines secondary to the superimposition of disuse on biological ageing.
As noted above, ageing is associated with declines in muscle function and cardiorespiratory fitness, resulting in an impaired capacity to perform daily activities and maintain independent functioning.47‐49 Insufficiently active individuals lose large amounts of muscle mass over the course of adult life (20–40%), and this process plays a significant role in the similarly large losses in muscle strength observed in both cross‐sectional and longitudinal studies,50 with the combination
