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 | Aerobic: 30–60 min/session Resistance: 2–3 sets of 8–10 repetitions of 6–8 muscle groups | 2–3 sets of 8–10 repetitions of 6–8 muscle groups | 2–3 sets of 8–10 repetitions of 6–8 muscle groups |
| 50 jumps per session for high impacta | |||
| 2–3 repetitions of 5–10 different static and dynamic balance postures | |||
| Intensity | Aerobic: 60–75% of maximum exercise capacity (VO2 max or maximum heart rate) or 13–14 on the Borg Scale of perceived exertion Resistance: 70–80% of maximum strength (one repetition maximum) exertion | 70–80% of maximum capacity (one repetition maximum) | 70–80% of maximum capacity (one repetition maximum) as load |
| 5–10% of body weight in vest during jumps; jumps or steps of progressive height | |||
| Practice the most difficult balance posture not yet mastered |
a Thus far proven only in premenopausal women or when combined with resistance training in older adults.
Physical activity and bone health
A wealth of animal and human data provide evidence for a relationship between physical activity and bone health at all ages. Mechanical loading of the skeleton generally leads to favourable site‐specific changes in bone density, morphology, or strength, whereas unloading (in the form of bed rest, immobilisation, casting, spinal cord injury, or space travel) produces rapid and sometimes dramatic resorption of bone, increased biochemical markers of bone turnover, changes in morphology such as increased osteoclast surfaces, and increased susceptibility to fracture.
Comparative studies of athletic and non‐athletic populations usually demonstrate significantly higher bone density in the active cohorts, ranging from 5 to 30% higher, depending on the type, intensity, and duration of exercise training undertaken and the characteristics of the athletes studied. Exceptions occur with non‐weight‐bearing activities such as swimming, cycling, or amenorrhoeic or competitive distance runners, whose bone density appears similar to or lower than that of controls. Similarly, on a smaller scale, differences are often observed between habitually active and sedentary non‐athletic individuals. Experimental evidence in animal models and also some human data suggest that changes in bone strength not directly correlated with density may contribute to the overall benefits of mechanical loading for skeletal integrity and resistance to fracture (e.g., increased bone volume or altered trabecular morphology) so that evaluating bone density changes alone likely significantly underestimates the skeletal benefits of loading.
Consistent with the bone density findings noted above, hip fracture incidence has been observed to be as much as 30–50% lower in older adults with a history of higher levels of physical activity in daily life, compared with age‐matched, less active individuals. For example, in the prospective Epidemiology of Osteoporosis Study (EPIDOS) study of 6901 white women over the age of 75 followed for 3.6 years, investigators found that a low level of physical activity increased the risk for proximal humerus fracture by more than twofold. The relative risk of fracture in sedentary women (RR = 2.2) was greater than that attributable to low bone density (RR = 1.4), maternal history of hip fracture (RR = 1.8), or impaired balance (RR = 1.8). The interaction of these risk factors is indicated by the fracture rate, which rose from about 5 per 1000 woman‐years in individuals with either bone fragility or high fall risk to 12 per 1000 woman‐years for women with both types of risk factors. Such data suggest the great potential utility of multifactorial prevention programmes for osteoporotic fracture that can address both bone density and fall risk (sedentary behaviour, sarcopenia, poor balance, polypharmacy, etc.) simultaneously.
Exercise intervention trials in postmenopausal women and older men
Significant changes in the femur, lumbar spine, and radius have been seen following high‐impact aerobic training, resistance training, and combined programmes of aerobic and resistive exercise. Unlike results obtained in younger women, isolated high‐impact training (jumping, skipping, heel drops) has not yet been found to be effective in studies of postmenopausal women. High dropout rates (30–50%) are problematic in these trials, raising the issue of generalisability and sustainability of the outcomes observed. This is particularly relevant to fracture prevention efficacy of exercise, as several studies have shown complete or partial reversal of gains in bone mineral density (BMD) after the cessation of training.
For older men and women, a combination of decreased anabolic hormones (oestrogen, testosterone, growth hormone), increased catabolic milieu (higher leptin and cortisol associated with visceral adipose tissue), the emergence of musculoskeletal and other diseases, retirement, and reduced recreational activities have a major negative impact on both bone and muscle tissue. The majority of studies demonstrating the efficacy of exercise on bone density have been conducted in women between 50 and 70 years of age, and it is not yet known if efficacy would be similar in women over 80 with multiple comorbidities,