Osteoporosis is a condition marked by reduced bone strength leading to an increased risk of fractures. It is one of the world’s most common chronic conditions. It typically begins with an unnoticed decrease in bone mass that leads to structural deterioration of bone tissue and an increased susceptibility to fractures of the hip, spine and wrist. However, any bone can become susceptible to change in strength, particularly with age.1
Osteoporosis affects one in three women over 50 worldwide (more than breast cancer) and one in five men (more than prostate cancer).2 The incidence of osteoporosis is increasing at rates faster than would be predicted by the increase in the proportion of aged individuals.3 It was once thought of as a disease of ‘little old ladies’, but is now considered by many researchers as a paediatric disorder that manifests itself in old age.4
The two generally accepted strategies to make bones more resistant to fracture are: maximising the gain in bone mineral density (BMD) in the first three decades of life, and minimising the decline in BMD after the age of 40 due to menopause in women, ageing, a decline in physical activity and medical illnesses.
Maintaining a vigorous level of physical activity across the life span should be viewed as an essential component for achieving and maintaining good bone health. Physical activity and exercise increases peak bone mass, minimises age-related bone loss and prevents falls and subsequent fractures. Exercise is the only intervention that can potentially both increase bone mass and strength, and reduce the risk of falling in older populations.3
Building up a ‘bone bank’
Peak bone mass and strength, which is achieved in the third decade of life, predicts future fracture risk. A high peak bone mass, or a large ‘bone bank account’, reduces the likelihood of breaking a bone or developing osteoporosis later.
Research has also shown that the rate at which bone mineral is accrued is highest during late childhood and early adolescence. Therefore, it is critical to promote bone-healthy behaviours in children and teens.4
By age 18, bone density is almost complete and our bodies have 98% of their skeletal mass. Although some young adults will continue to gain a small amount of bone until age 25 when they reach peak bone mass.
One study in Finland shows that the most physically active young girls gain about 40% more bone mass than the least active girls of the same age. Similar, but less dramatic results were recorded for boys in a US survey.2
Studies comparing athletes from different sports have shown the highest bone mineral density values in athletes participating in sports associated with high-impact forces (eg. gymnastics, volleyball, and basketball), and in sports that require variable or ‘odd-impact’ loads to the skeleton (eg. soccer, tennis and handball).
In addition to impact loading from jumping and sprinting activities, bone also adapts favourably to high joint reaction forces from vigorous muscular contractions, such as in weight lifting or resistance training. These types of activities should be considered when planning exercise programmes for children and teens.
Several randomised controlled exercise interventions have also provided insight into the frequency and duration of exercise needed to build bone in young girls. Programmes in which jumping and running games were added to physical education classes for approximately 10-30 minutes, three days per week during the school year have shown significantly greater gains in bone mineral at the hip and lumbar spine in prepubertal and early pubescent girls, compared to girls who participated in regular physical education exercise activities. From these studies we can conclude that brief sessions of vigorous impact exercise, three days per week, can promote bone health throughout the developmental years.
Young girls need to learn and practise these bone-healthy behaviours in order to optimise their bone mass and bone strength in adulthood and thus decrease their risk of osteoporosis in old age.4
Maintaining a ‘bone bank’
Bone mass may remain stable or decrease very gradually for a period of years. It can be affected by several factors, including heredity, diet, sex hormones, physical activity, lifestyle choices and the use of certain medications.1 Starting in midlife, both men and women experience an age-related decline in bone mass. Women lose bone rapidly in the first four to eight years after menopause, which usually occurs between ages 45 and 55. By age 65, men and women tend to lose bone tissue at the same rate, and this more gradual bone loss continues throughout life.
Muscles also age. Sarcopenia is the term used to describe loss of skeletal muscle mass with declining functional muscle strength and muscle size, in conjunction with muscle atrophy. The changes in muscle size, and ultimately strength levels, are related to the loss of muscle fibres and the shrinking of remaining fibres.
Under normal conditions, human muscle strength in women and men reaches its peak between 20-30 years of age, after which it remains virtually unchanged for another 20 years. After this point muscular performance deteriorates at a rate of about 5% per decade, amounting to a 30-40% loss of functional strength over the adult life span.
Variations in the rate of loss reflects the diversity of occupations, physical activity backgrounds, muscles used, and type of muscle contractions.1
One of the hallmark features of ageing is loss of bone strength, loss of muscle mass and strength, and loss of oestrogen in women. Although the debate continues as to the cause of this loss, one thing is certain: the inclusion of regular strength training exercise sessions will play an important role in delaying and reducing age- or inactivity-associated loss experience.1
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Muscle-strengthening exercises
Muscle-strengthening exercises include activities where one moves their body, a weight or some other resistance against gravity. They are also known as resistance exercises and include lifting weights, using elastic exercise bands, using weight machines, lifting one’s own body weight, or functional movements such as standing and rising up on the toes.5
Strength training provides the mechanical stress or load that stimulates the development of muscle and bone strength. The adaptations of muscles as a result of regular strength training sessions include strength changes and muscle mass improvement. A consequence of these improvements is the fact that the muscle is now capable of providing a stronger contraction and the advantage of this is that muscle contraction is the dominant source of skeletal loading that provides the mechanical stimulus to increase bone.1
The ideal exercise regime for maintaining or promoting bone and muscle health is strength training. Strength training can be site-specific, individualised, progressively overloaded and adjustable. Strength training also provides other benefits, such as improved balance and co-ordination.
To achieve strength changes, a minimum of two sessions a week for 45-60 minutes beginning at 70% of one repetition maximum (1RM) and building to 85% 1RM would be appropriate.1 However, particularly with the osteopaenic and osteoporotic patient groups, the risk of injury must be considered when attempting a 1RM. Multiple repetition sets (eg. eight repetitions of 10%1RM) should be performed.
The large muscle groups in the upper and lower limbs should be targeted using loaded functional exercise. Suggestions include sit to stand or calf raises (with weighted vests if necessary). These exercise programmes should be prescribed and progressed by a chartered physiotherapist as assessments are required to determine the efficiency and effectiveness of the training programme.
Weight-bearing exercises
Weight-bearing physical activity has beneficial effects on bone health across the age spectrum. These include activities where the body is moved against gravity while staying upright. Weight-bearing exercises can be high or low-impact. High-impact exercises help build bones and keep them strong, eg. dancing, high-impact aerobics, hiking, jogging or running, skipping rope, stair climbing and tennis.
Low-impact weight-bearing exercises can also help keep bones strong and are a safe alternative if higher impact is not appropriate. Examples include using cross trainer machines, low-impact aerobics, using stair or step machines and fast walking.5
During adulthood, the primary goal of physical activity for bone health should be to maintain bone mass. Whether adults can increase BMD significantly remains equivocal. When increases have been reported, it has been in response to relatively high intensity weight-bearing endurance or resistance exercise; gains in BMD do not appear to be preserved when the exercise is discontinued.
Observational studies suggest that the age-related decline in BMD is attenuated, and the relative risk for fracture is reduced, in people who are physically active, even when the activity is not particularly vigorous. However, there have been no large randomised controlled trials to confirm these observations, nor have there been adequate dose-response studies to determine the volume of physical activity required for such benefits.3
The benefits of weight-bearing exercise therapy for preserving bone density in postmenopausal women are unclear.
Martyn-St James and Carroll6 concluded from their systematic review and meta-analysis that impact exercise in the form of jogging, when combined with other low-impact activity such as stair climbing and walking, and programmes combining impact exercise with high magnitude exercise in the form of resistance training, have a positive effect on preserving bone mineral density in postmenopausal women. Where appropriate, specific modes of impact activity need to be integrated into well-designed and safe exercise programmes for postmenopausal women.6
Fall prevention
Many factors contribute to falling, including diminished postural control, poor vision, reduced muscle strength, reduced lower limb range of motion, and cognitive impairment. Extrinsic factors include psychotropic medications and tripping hazards.
Exercise interventions are effective in reducing falls only if they are directed to individuals in whom the cause of falling involves factors that are amenable to improvement with exercise, eg. poor muscle strength, balance or range of motion.
Reviews and meta-analyses of randomised trials suggest that exercise trials that included balance, leg strength, flexibility, and/or endurance training effectively reduced risk of falling in older adults.3
Non-impact exercises can help to improve balance, posture and functional performance. These exercises can also help to increase muscle strength and decrease the risk of falls and fractures.
Balance exercises that strengthen legs and test balance, such as tai chi, can decrease falls risk. Meanwhile, posture exercises that improve posture and reduce rounded or ‘sloping’ shoulders can help decrease the chance of fracture, especially in the spine.
Functional exercises that improve quality of movement will assist with performance of daily activities and decrease falls and subsequent fracture risk.5 Yoga and pilates can also improve strength, balance and flexibility. The key message is that fall prevention is essential and falls risks may be reduced with exercise, balance and strength training.
The general recommendation that adults maintain a relatively high level of weight-bearing physical activity for bone health does not have an upper age limit, but as age increases, so does the need to ensure that physical activities can be performed safely. In light of the rapid and profound effects of immobilisation and bed rest on bone loss, and the poor prognosis for recovery of mineral after remobilisation, even the frailest elderly should remain as physically active as their health permits in order to preserve skeletal integrity.
Exercise programmes for elderly women and men should include not only weight-bearing endurance and resistance activities aimed at preserving bone mass, but also activities designed to improve balance and prevent falls.3
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The upside for graceful ageing is the ability of elderly individuals to respond to exercise with large gains in strength, mobility and physical fitness. Exercise studies have repeatedly demonstrated the capacity of older muscle to adapt to specifically designed training programmes, resulting in gains in both strength and muscle size regardless of age or gender. If the independent performance of many daily living activities is strength-dependent, then the maintenance of muscle size and functional strength should play an important role in the training regime for older adults.
As the human body inevitably advances toward old age, it is becoming more evident that exercise in the form of strength training and weight-bearing activity are providing the answers to slowing age-related changes in bones and muscles.1 See Table 2 for exercise recommendations.5
References
Humphries BD. Strength Training for Bone, Muscle, and Hormones [Internet]. Indianapolis: American College of Sports Medicine; (undated). Available from: www.acsm.org/docs/current-comments/strengthtrainingforbmh.pdf
International Osteoporosis Foundation. Exercise Vital To Build Strong Bones [Internet]. International Osteoporosis Foundation; 2012. Available from http://www.iofbonehealth.org/exercise-vital-build-strong-bones
Kohrt WM. American College of Sports Medicine Position Stand Physical Activity and Bone Health [Internet]. Indianapolis: American College of Sports Medicine (undated). Available from: http://www.acsm.org/access-public-information/position-stands/position-stands/lists/position-stands/physical-activity-and-bone-health
Nichols J. American College of Sports Medicine “Exercise is Medicine” for Building Strong Bones in Adolescent Girls [Internet]. Indianapolis: American College of Sports Medicine; 2011[2011 Oct 04]. Available from: http://www.acsm.org/access-public-information/articles/2011/10/04/-exercise-is-medicine-for-building-strong-bones-in-adolescent-girls
National Osteoporosis Foundation. Exercise for Strong Bones [Internet]. Washington: National Osteoporosis Foundation; (undated). Available from: http://www.nof.org/prevention/exercise.htm
Martyn-St James M, Carroll S. A meta-analysis of impact exercise on postmenopausal bone loss: the case for mixed loading exercise programmes. Br J Sports Med 2009; 43: 898-908
Minne H.M. Invest in your bones. Move it or Lose it. How exercise helps to build and maintain strong bones, prevent falls and fractures, and speed rehabilitation [Internet]. London: International Osteoporosis Foundation; 2012 [2005 June]. Available from: http://www.iofbonehealth.org/sites/default/files/PDFs/WOD%20Reports/move_it_or_lose_it_en.pdf
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