RHEUMATOLOGY
Exercise and osteoporosis
Exercise in the form of strength training and weight-bearing activity work to slow down age-related changes in bones and muscle
December 1, 2012
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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