that impact exercise capacity, muscle mass cannot usually be maintained into old age even with regular aerobic activities in either general populations or master athletes. Only overloading muscle with weight‐lifting exercise (resistance training) has been shown largely to avert losses of muscle mass (and strength) in older individuals. For example, Klitgaard et al.51 found that elderly men who swam or ran had age‐related reductions in muscle size, strength, and metabolism similar to their sedentary peers, whereas the muscle of older men who had been weight‐lifting for 12–17 years was almost indistinguishable, and even superior in some aspects, to that of healthy men 40–50 years younger than them.
Skeletal muscle power decreases to an even greater extent than muscle strength with advancing age48,52 and is more strongly associated with functional test performance than muscle strength in older populations,52,53 as well as being important for balance54 and fall risk. One of the major contributing factors to the loss of strength and power is a gradual of reduction in cycles of degeneration/regeneration of spinal motor neurons. Partial functional muscle denervation following by reinnervation of abandoned fibres is also believed to occur, resulting in an increased size of remaining motor units (type grouping) that results in impaired force steadiness and fine motor control with ageing.53,55,56 Moreover, age‐related decline in strength may also be due to decreased maximal voluntary activation of the agonist muscles or changes in degree of agonist‐antagonist coactivation.57
This age‐related loss of spinal motor neurons leads to a decline in the size and/or number of individual muscle fibres, especially fast‐twitch fibres.58,59 The consequences include impaired mechanical muscle performance (i.e., reduced maximal muscle strength, power) that can adversely affect an older person's ability to remain functionally independent to perform daily activity tasks60 (e.g., walking, stair climbing, rising from a chair). Along with a decrease in muscle size, ageing is also associated with a decrease in muscle quality due to increased amount of intramyocellular adipose tissue and connective tissue.61,62 Physical inactivity greatly exacerbates the catabolism and atrophy of skeletal muscle associated with normal ageing.
Many studies suggest that habitual engagement in physical activity/exercise can markedly attenuate most decrements in exercise capacity that would otherwise occur with ageing (see Tables 7.1–7.4), with the notable exception of maximal heart rate (due to declining sensitivity to β‐adrenergic stimulation in the ageing heart).63 Although the peak exercise workload achievable is therefore always lower in aged individuals, the cardiovascular and musculoskeletal adaptations to chronic aerobic exercise enable the trained individual to sustain higher submaximal workloads with less of a cardiorespiratory response (heart rate, blood pressure, and dyspnoea) and also less overall and musculoskeletal fatigue. However, exercise adaptation is specific to the modality chosen, with some overlap. Aerobic capacity is best addressed with moderate‐ to‐ vigorous‐ntensity aerobic exercise, with the greatest benefits seen when high‐intensity interval training (HIIT, 85–95% peak heart rate for 1–4 minutes intervals) is undertaken. However, HIIT has been primarily studied in healthy and cardiovascular cohorts, in whom its efficacy and safety have been well‐reported64; its feasibility in frail older adults with multiple comorbidities remains to be established. High‐intensity resistance training is the optimal prescription to address sarcopenia and may also enhance balance.65 Less well known is that resistance training improves aerobic capacity to a similar extent as moderate‐intensity aerobic training in older adults,66 thus targeting the two major changes in exercise capacity of ageing with one efficient prescription. Importantly, aerobic exercise does not enhance strength or balance and is thus insufficient as an isolated prescription for most older adults. Systematic reviews clearly indicate that falls‐prevention programmes inclusive of walking are inferior to those focusing on strength and balance exercises and have also been associated with increases in osteoporotic fracture rates in those at risk.67
Similar to aerobic and resistance training, there is evidence that balance training and flexibility training68 induce adaptations in associated fitness declines in these areas. Balance enhancement is clearly related to reduction in fall risk67 and also functional mobility. Although stretching is generally included in most position stands,7,79 there is limited evidence that improvements in flexibility by themselves are associated with important clinical outcomes. Therefore, it is best conceptualised as a component of cool‐down after the actual exercise session has been completed. Stretching prior to exercise has not been shown to reduce musculoskeletal injuries as once thought and in fact results in reduced post‐stretching muscle performance. The best warm‐up for cardiovascular and musculoskeletal systems is simply to do what is about to be done but at a lower intensity. This may mean, for example, walking at a slow pace or performing a set of weightlifting repetitions with a light load.
Optimisation of body composition with ageing
‘Usual ageing’ is associated with significant losses of bone and muscle (lean mass) and increases in adipose tissue, along with central and visceral shifts in the regional distribution of adipose tissue stores. The extent to which these changes occur in an individual depends on a combination of genetic‐, lifestyle‐, and disease‐related factors that are all interrelated.69 All of these body composition changes may negatively affect metabolic, cardiovascular, and musculoskeletal function,6 even in the absence of overt disease, and therefore it is important to anticipate them and optimise lifestyle choices and other treatments that can counteract the negative effects of ageing and/or disease on body composition. As detailed in the sections that follow and outlined in Table 7.5, one of the most potent pathways from physical activity to health status involves modulating these age‐related shifts in body composition by habitual exercise patterns.
Role of exercise and physical activity in bone health and fracture risk
Age‐related changes in bone
Bone mass begins to decrease well before menopause in women (as early as the 20s in the femur of sedentary women) and accelerates in the perimenopausal years, with continued declines into late old age. Similar patterns are seen in men, without the acceleration related to loss of ovarian function seen in women. As with losses of muscle tissue (sarcopenia), many factors related to genetics, lifestyle, nutrition, disease, and medication enter into predicting bone density at a given age.
Table 7.5 Exercise recommendations targeting optimal body composition for older adults.
| Exercise recommendations | Decreased adipose tissue mass and visceral deposition | Increased muscle mass and strength | Increased bone mass and density and reduced fracture risk |
|---|---|---|---|
| Modality | Aerobic or resistance training | Resistance training | Resistance training |
| High‐impact activities (jumping using weighted vest during exercise) if tolerated by joints | |||
| Balance training | |||
| Frequency | Aerobic: 3–7 days/week Resistance: 3 days/week | 3 days/week | Resistance training: 3 days/week |
| Balance training: up to 7 days/week | |||
| Volume |
