L22 RDA Normal aging and problems of mobility

Overview

This lecture covers the demographic and societal context of an ageing population (globally and in New Zealand), attitudes towards ageing, frameworks for “ageing well” (compression of morbidity), the physiological changes of normal ageing (especially muscle and bone), the burden of physical inactivity on health systems, and the role of exercise (dose-response principles and specific benefits, including strength training) in mitigating age-related decline in mobility and independence.

Ageing population trends

• Population ageing is a global and NZ-specific trend: global 65+ and 80+ counts are both rising steeply, with 65+ projected to reach ~6.7 million and 80+ ~4.5 million by 2050.
• In New Zealand, the number of people aged 65+ doubled since 1980 and is projected to double again by 2036; the proportion of the population aged 65+ is projected to rise from ~10% (1981) to ~28% by 2068.
• Global life expectancy rose from 66.8 years (2000) to 73.4 years (2019), an increase of 6.6 years. Healthy life expectancy (HALE) rose from 58.3 to 63.7 years over the same period, an increase of only 5.4 years. This means HALE has not kept pace with life expectancy: extra years of life are not matched by extra years of good health.
• Regional NZ disparity: the number of districts where 1 in 4 people are 65+ was projected to rise from 2 (2015) to 48 (2033); 17 districts were projected to see population decline. Consequences: smaller towns become disproportionately older than cities, local services must adapt, some regions face declining rate bases and skilled-worker shortages, and older people in remote areas may struggle to access health and transport services.
• Older people are a growing economic force: spending by people 65+ was projected to rise from $14b(2011)to$39b (2031, 2013 dollars); paid employment among 65+ was projected to rise from 27% (~138,000 people, 2015) to 31% (~150,000 people, 2031). Only 14–18% of employers were actively planning for an ageing workforce.
• The older population is becoming more ethnically diverse. Māori and Pacific populations are younger overall than NZ European, so most existing services for older people are aimed at NZ Europeans. Projected 65+ growth 2015→2035: NZ European 590,000→780,000 (63%), Pacific 18,000→31,000 (163%), Māori 41,000→70,000 (184%), Asian 39,000→88,000 (281%). Implication: growing demand for multicultural and non-English-language services in home support and aged residential care.

Attitudes to ageing and positive ageing

• Older adults with negative attitudes towards ageing showed slower walking speed and worse cognitive ability two years later than those with more positive attitudes.
• Gerontologist Erdman Palmore’s survey found more than 75% of people over 60 had experienced one or more incidents of ageism.
• Negative attitudes towards ageing are deeply rooted in modern societies, present from as young as pre-school age, and societal attitudes towards ageing are predominantly negative — despite everyone eventually growing older; persistence of these attitudes continues to diminish quality of life.

Compression of morbidity (ageing well framework)

• Compression of morbidity (James Fries, 1980): a hypothesis of healthy ageing proposing that total lifetime morbidity (disability, frailty, infirmity, impairment of activities of daily living, ADLs) can be compressed into a shorter span of time at the end of life, rather than extended.
• Contrasted with two other patterns: “present morbidity” (morbidity begins partway through life and expands progressively to death) and “life extension” (morbidity onset is shifted later and death is pushed further out, without compressing the morbid period).
• Four strategies to achieve compression of morbidity:
  1. Primordial prevention — preventing risk factors themselves from developing (e.g. smoking, childhood obesity).
  2. Primary prevention — reducing the prevalence of existing risk factors.
  3. Secondary prevention — preventing disease progression via early detection/treatment (e.g. hypertension).
  4. Tertiary prevention — reducing morbid states that have already occurred.
• Determinants of major end-of-life disabling conditions (cardiac disease, respiratory disease, reduced mobility following falls/fractures, accelerated cognitive loss) commence in mid- or early life, so reducing late-life disability requires acting earlier in the life course.
• The Lancet life-course model of dementia risk factors: early life (less education, ApoE ε4 allele), midlife (hearing loss, hypertension, obesity), late life (smoking, depression, physical inactivity, social isolation, diabetes). Overall, 35% of dementia risk factors are potentially modifiable and 65% are non-modifiable.

Normal ageing: definitions and physiological changes

• Normal ageing is associated with changes that increase vulnerability to accidents or disease, but ageing itself is not a disease. Unlike disease, ageing changes occur inevitably in every organism given enough time and affect all species after the age of conception. Advanced age is a risk factor for many diseases.
• Three ways to conceptualise age: chronological age, functional age, subjective age.
• Age-related disease categories by organ system (from the ageing-related disease diagram): brain ageing and neurodegenerative disease (Alzheimer’s disease, cognitive dysfunction, dementia), eye disease (age-related macular degeneration), skin disease, circulatory disease (coronary heart disease, hypertension), metabolic disease (diabetes, obesity), joint degeneration, vascular lesions (atherosclerosis).
• Physiologic changes with age (Table 7.2):
  • Unchanged: resting heart rate.
  • Lower: maximum heart rate, maximum cardiac output, absolute/relative maximum oxygen uptake reserve (VO2Rmax), vital capacity, muscular strength, flexibility, bone mass, fat-free body mass, glucose tolerance.
  • Higher: resting and exercise blood pressure, residual volume, % body fat.
  • Slower: reaction time.
  • Longer: recovery time.

Musculoskeletal ageing: muscle

• Sarcopenia: a syndrome characterised by progressive and generalised loss of skeletal muscle mass and strength, with risk of adverse outcomes such as physical disability, poor quality of life and death (definition from the European Working Group on Sarcopenia in Older People). The term derives from Greek sarx (flesh) and penia (loss) — “poverty of flesh.”

  .

• Ageing-associated changes in muscle tissue:
  1. Shift from fast type II muscle fibres towards slow type I muscle fibres.
  2. Deposition of lipids within and between muscle fibres (myosteatosis/fat infiltration), without necessarily any loss in overall body weight.
• Muscle quality (fat infiltration) is influenced by activity level, not just age: MRI comparisons showed a 40-year-old triathlete with lean muscle, a 70-year-old sedentary person with marked adipose infiltration around the quadriceps, and a 74-year-old triathlete with muscle quality closer to the younger athlete than to the sedentary 70-year-old — illustrating that activity level, not age alone, drives muscle quality decline.

Musculoskeletal ageing: bone

• Bone mass follows a life-course pattern: active growth, then from the mid-30s onward a phase of slow loss, followed (particularly after menopause in women) by a phase of rapid loss, then a phase of less rapid loss. Women lose bone mass faster after menopause, but bone loss occurs in men too.
• Osteoporosis: a condition characterised by decreased bone density, decreasing bone strength and resulting in fragile, abnormally porous (“sponge-like”) bone that is compressible; weakens the skeleton and results in frequent fractures.
• Osteopenia: bone that is slightly less dense than normal bone, but not to the degree of osteoporosis.
• Microscopic comparison: normal bone shows a denser trabecular lattice; osteoporotic bone shows a sparser, more porous lattice.

The cost and scale of physical inactivity

• Physical inactivity is an important modifiable risk factor for non-communicable diseases (NCDs) and mental health conditions (Santos et al., Lancet Global Health, 2022).
• Global projection: 499.2 million new cases of preventable major NCDs would occur globally by 2030 if physical inactivity prevalence does not change, with direct health-care costs of INT$520billion;theglobalcostofinactionwouldreachINT$47.6 billion per year.
• 74% of new NCD cases would occur in low- and middle-income countries, but high-income countries would bear a larger share (63%) of the economic costs.
• Disease outcomes considered: coronary heart disease, stroke, type 2 diabetes, hypertension, several cancers (breast, colon, bladder, endometrial, oesophageal, gastric, renal), dementia, depression.
• Disproportionate cost burden: dementia accounted for only 5% of new preventable NCDs but 22% of all costs; type 2 diabetes accounted for 9% of new preventable cases but 25% of costs; cancers accounted for 1% of new preventable cases but 15% of costs.
• NZ health service context (DHB, 2016): older people accounted for 42% of health services; spend was skewed toward treatment over prevention (a 0.4 cent–18 cent split); and there was a 9–91 split between active and inactive older adults (i.e. most older adults are inactive).
• Illustrated historically as a “March of Progress”-style sequence from ape to upright hunter-gatherer to cyclist to a person using a walking frame to a person seated in a wheelchair — depicting a societal/technological trend toward increasing sedentary behaviour, in contrast to the physical activity levels of hunter-gatherer ancestors.

Physical activity: definitions and current levels

• Leisure-time physical activity: an activity undertaken in an individual’s discretionary time that increases total daily energy expenditure.
• Sport: part of the physical activity spectrum; any institutionalised, organised practice governed by specific rules.
• Exercise: a sub-category of leisure-time physical activity involving planned, structured and repetitive bodily movements performed to improve or maintain one or more components of physical fitness.
• NZ activity levels, 2021/22:
  • 12.8% (1 in 8) of adults (~533,000) were active for less than 30 minutes per week.
  • 35.3% (about 1 in 3) of adults (~1,467,000) did at least 30 minutes but less than 2.5 hours per week.
  • 51.9% (about half) of adults (~2,155,000) did at least 2.5 hours of activity per week.
  • Critical viewpoint raised: can self-reported physical activity be measured accurately?

  . Common figures cited across guidelines include 150 minutes of moderate-intensity (or 75 minutes vigorous-intensity) aerobic activity per week plus muscle-strengthening activity twice per week.

Principles of exercise prescription and benefits

• Principles for dose-response in exercise prescription:
  1. Overload — the stimulus must exceed what the body normally experiences.
  2. Progression — the stimulus must increase over time to continue producing adaptation.
  3. Specificity — training adaptations are specific to the type of stimulus applied.
• A dose-dependent response curve rises from worse to better with increasing dosage, with a “threshold range” representing the best balance of benefits and safety (i.e. more is not indefinitely better; there is an optimal zone).
• Health benefits of physical activity (PA): healthier body composition and increased muscle mass, improved functional health, increased bone density, improved sleep quality, enhanced performance of work/recreational/sport activities, enhanced feelings of well-being, decreased anxiety and depression, plus additional specific physiological/physical benefits for people with chronic health conditions and special populations (e.g. older adults, pregnancy).
• Benefits of strength (resistance) training specifically:
  • May delay loss of muscle mass and preferentially targets type II muscle fibres.
  • Improves overall muscle strength and produces lean mass gains.
  • Assists young women in attaining peak bone mass, and can increase and maintain bone mineral density in general → contributes to reduction in the rate of sarcopenia and osteoporosis.
  • Improves insulin sensitivity.
  • Older men and women can achieve similar or greater strength gains than younger adults with resistance exercise, provided the stimulus is sufficient.
  • Eccentric actions may preferentially reduce the rate of decline in muscle quality.

Conclusions

• Population ageing is occurring and is framed positively (“a wonderful thing”).
• Muscle strength and bone strength are critical to independence but decline from middle age onward; both are affected by lifestyle and disease.
• Muscle weakness and osteoporosis are both amenable to prevention and treatment.
• Strength training reduces the rate of sarcopenia and osteoporosis.

Self-test

1. Define compression of morbidity and name the person who proposed the hypothesis.
2. List the four strategies for morbidity compression, with one example of each.
3. Distinguish normal ageing from disease, referencing why ageing itself is not classified as a disease.
4. Describe the two ageing-associated changes in muscle tissue described in the lecture, and what MRI comparisons between a sedentary and an active older adult illustrate about muscle quality.
5. Define sarcopenia, including the source of its Greek etymology.
6. Distinguish osteoporosis from osteopenia.
7. Describe the pattern of bone mass change across the life course, including the sex difference.
8. List three physiologic variables that are lower with age and three that are higher with age, according to Table 7.2.
9. A patient asks whether her life expectancy gains mean she will also gain the same number of healthy years. Using the global HALE vs life expectancy figures from the lecture, explain why this is not necessarily true.
10. State the three principles for dose-response in exercise prescription, and explain the significance of the “threshold range” on the dose-response curve.
11. List four benefits of strength training relevant to musculoskeletal health in older adults.
12. Using the NZ 2021/22 physical activity statistics, describe the proportion of adults meeting different activity thresholds.
13. Explain how the lecture links physical inactivity, disease burden, and the demographic trend of an ageing population into a single overall problem for health care systems.

Answers

Reveal answers

1. Compression of morbidity is the hypothesis that total lifetime morbidity (disability, frailty, infirmity, impairment of ADLs) can be compressed into a shorter period at the end of life rather than extended across more years. Proposed by James Fries in 1980.
2. Primordial prevention (preventing risk factors like smoking or childhood obesity from developing), primary prevention (reducing prevalence of existing risk factors), secondary prevention (early detection/treatment to prevent disease progression, e.g. treating hypertension early), tertiary prevention (reducing morbid states that have already occurred).
3. Normal ageing increases vulnerability to accidents or disease but is not itself a disease: unlike disease, its changes occur inevitably in every organism given time and affect all species after conception, whereas disease is not universal or inevitable in this way. Advanced age is instead a risk factor for many diseases.
4. (1) A shift from fast type II muscle fibres to slow type I fibres; (2) deposition of lipids within and between muscle fibres, without necessarily any loss of overall body weight. The MRI comparison (40-year-old triathlete vs 70-year-old sedentary vs 74-year-old triathlete) shows that muscle quality (fat infiltration) is driven more by activity level than by chronological age alone, since the older triathlete’s muscle quality resembled the younger athlete’s rather than the sedentary 70-year-old’s.
5. Sarcopenia is a syndrome of progressive, generalised loss of skeletal muscle mass and strength, with risk of adverse outcomes such as physical disability, poor quality of life and death (European Working Group on Sarcopenia in Older People). The name derives from Greek sarx (flesh) and penia (loss), meaning “poverty of flesh.”
6. Osteoporosis is a decrease in bone density causing fragile, abnormally porous (“sponge-like”), compressible bone with frequent fractures. Osteopenia is bone that is slightly less dense than normal but not to the degree seen in osteoporosis.
7. Bone mass shows active growth early in life, then from the mid-30s a phase of slow loss, then a phase of rapid loss (more pronounced and earlier in women after menopause), followed by a phase of less rapid loss. Bone loss occurs in men as well as women, but women’s loss accelerates faster after menopause.
8. Lower with age: maximum heart rate, maximum cardiac output, VO2Rmax, vital capacity, muscular strength, flexibility, bone mass, fat-free body mass, glucose tolerance (any three). Higher with age: resting/exercise blood pressure, residual volume, % body fat (any three).
9. No — between 2000 and 2019, global life expectancy rose by 6.6 years but healthy life expectancy (HALE) rose by only 5.4 years, because the increase was driven by declining mortality rather than by a reduction in years lived with disability. So extra years of life are not fully matched by extra years of good health.
10. Overload (the stimulus must exceed what the body is used to), progression (the stimulus must increase over time to keep producing adaptation), specificity (adaptations are specific to the stimulus applied). The threshold range on the dose-response curve represents the dosage zone giving the best balance of benefits and safety, i.e. an optimal range rather than “more is always better.”
11. Any four of: delays loss of muscle mass and targets type II fibres; improves overall muscle strength and lean mass; assists in attaining peak bone mass in young women and can increase/maintain bone mineral density (reducing sarcopenia and osteoporosis rates); improves insulin sensitivity; can produce strength gains in older adults similar to or greater than in younger adults if stimulus is sufficient; eccentric actions may preferentially slow decline in muscle quality.
12. In 2021/22, 12.8% of adults (~533,000) did less than 30 minutes of activity per week; 35.3% (~1,467,000) did between 30 minutes and 2.5 hours; and 51.9% (~2,155,000) did at least 2.5 hours per week.
13. An ageing population combined with age-related physiological decline (e.g. sarcopenia, osteoporosis) and the rising burden of non-communicable diseases creates a large and growing burden on health-care systems; physical inactivity is a major modifiable driver of this burden (contributing hundreds of millions of preventable NCD cases and hundreds of billions in health-care costs globally), so addressing inactivity is presented as a key lever for compressing morbidity and reducing the strain of an ageing population on health services.