Osteoporosis is a common medical problem. Lifestyle measures to prevent or help treat existing osteoporosis often only receive lip service. The evidence for the role of exercise in the prevention and treatment of osteoporosis is reviewed….. read more
The association between mechanical stress
and bone mass was first recorded by Galileo in 1683 who noted the relationship
between body weight and bone size; but it was not until 1892 that Julius Wolff,
a German anatomist realised that changes in the mechanical stresses applied to
a bone influenced bone strength.1 Immobility
or prolonged bed rest rapidly leads to hypercalcuria, negative calcium balance,
and bone loss.2 However
in paralysed individuals, weightbearing without muscle activity—for example,
assisted standing—does not decrease the urinary calcium losses or affect the
bone mass. From these findings, it would seem the duration and force of the
muscle activity on bone are important in maintaining bone mass.3 The
aim of this paper is to review the evidence for exercise preventing and
treating osteoporosis, with the protective effects against fracture also
CROSS SECTIONAL STUDIES OF EXERCISE AND BONE DENSITY
Many cross sectional studies have been
performed to investigate the effect of exercise and activity on bone mass.4–6 Most
studies have demonstrated a positive correlation between exercise levels and
bone mass. However cross sectional studies demonstrate simply an association,
and do not imply causation. Furthermore, the association is based on lifetime
exercise and does not mean that exercise in previous sedentary individuals can
prevent or reverse osteoporosis.
Observational studies assessing physical
activity by questionnaire have demonstrated an association between bone density,
childhood physical activity,7 current
physical activity,8 and
lifetime physical activity.9 Childhood
physical activity level was significantly related to calcaneal bone mineral
density (BMD) in 101 young women, but in the same study, the association with
current activity level did not reach statistical significance.7 Krall
and Dawson-Hughes using a validated questionnaire, studied participation in
outdoor walking and other leisure time physical activity in 239 postmenopausal
women. They found significantly increased whole body, leg, and trunk BMD in
women who walked more than 7.5 miles per week compared with women who walked
less than one mile per week. In this study, current walking activity reflected
lifelong walking habit.9 A
similar association between BMD and physical activity was reported in the
lumbar spine of postmenopausal women.10 BMD
correlated significantly with back muscle strength and level of current
physical activity. A physically active occupation has also been shown to be
important. Lifelong manual labour in men is associated with reduced rates of
bone loss from the metacarpal when compared with men in sedentary occupations.11 Two
groups have used objective methods to measure current physical activity. Aloia
and colleagues assessed current physical activity in 24 premenopausal women
using a motion sensor and found a significant independent association with BMD
at the spine, but not at the radius.12 However
other workers using a pedometer in premenopausal women failed to demonstrate an
association between current physical activity and BMD at any of the four
Pocock and co-workers were the first to
demonstrate a correlation between physical fitness (and by implication habitual
physical activity) and bone mass.14 They
objectively studied physical fitness in 84 healthy premenopausal and
postmenopausal women aged 20 to 75 years using predicted maximal oxygen uptake
(VO2 max) during a submaximal bicycle ergometer test. They
found VO2 max to be significantly associated with BMD at both
the femoral neck and spine, but not at the radius. In the 46 postmenopausal
women, physical fitness was the only significant predictor of femoral BMD. More
impressive evidence for an association between physical activity and BMD
results from the consistent association between muscle strength and BMD. Hand
grip strength has been shown to be positively associated with BMD at the radius
in postmenopausal women,15 and
a similar relationship has been described between lumbar spine BMD and back
Athletes v sedentary controls
Further support for an osteogenic effect of
exercise has come from studies comparing the BMD of recreational or elite
athletes in a variety of different sports with sedentary controls.4,5 Numerous
studies have shown higher bone density measurements in recreational or
competitive runners. In a study of male and female athletes over 50 years old
who had been long distance running for an average of nearly nine years, lumbar
bone mass was higher in women and men compared with sedentary controls.16 A
similar effect has been reported in male cross country runners when compared
with age matched sedentary controls.17 Runners
who had all been practising the sport for at least 25 years had significantly
increased bone mass in the calcaneus, femoral shaft, head of humerus, and
distal forearm bones. Weight or strength training is associated with
significantly increased BMD in athletes. Competitive weightlifters have significantly
increased lumbar spine BMD compared with sedentary age matched controls.18 Similarly,
increased BMD was reported at the spine of young women who took part in muscle
building activities compared with individuals whose physical activity was
Other weightbearing sports are also
associated with increased BMD. In a study of female college athletes and
sedentary controls, BMD measured at the calcaneus and lumbar spine was highest
in volleyball and basketball players and was significantly higher than
sedentary controls.20 In
this study, the BMD of swimmers was no different to the BMD of sedentary women.
Similarly Heinonen and colleagues in Finland compared BMD in female squash
players, aerobic dancers, and speed skaters with controls.21 Squash
players, speed skaters, and dancers had significantly increased BMD compared
with the control group, with differences in BMD parallelled by differences in
isometric muscle strength. Similar results have been described in young men
where spinal mineral density assessed by computed tomography was 14% greater in
active compared with sedentary men. Analysis of variance showed significant
differences in bone density based on type of exercise, with greatest bone
density seen in men taking aerobic and weightbearing exercise.22 It
is of note that two studies have shown that BMD is maintained in older subjects
in the medium term (5–7 years); these subjects previously had an intensive
exercise regimen but adopted a less intensive regimen.23,24
Unilateral limb studies
The effect of unilateral activity on one
limb of an individual has been studied and compared with the “non-exercising”
limb. This study design has the advantage of controlling for all other genetic
and environmental influences. These studies show a marked effect of exercise.5 In a
study of female squash players from Finland, BMD at the proximal humerus of the
racquet hand was 15.6% higher than the inactive arm and was significantly
related to the number of training years.25
Although numerous intervention studies have
been performed, many are poorly designed with no proper randomisation and
inadequate sample size. However we will review mainly randomised controlled
trials and only include other studies where randomised trials are lacking.
In a two year randomised controlled trial
127 women aged 20–35 years were allocated to either a high impact aerobic
exercise training programme, or to maintain their current activity levels or
participate in a programme of light stretching.26 Only
63 women completed the study (31 controls) but those in the exercise group
significantly increased their BMD at the spine, femoral neck, greater
trochanter, and calcaneus compared with the control group. Similar beneficial
effects have been reported in a small randomised controlled trial of jogging
and weight training for eight months. BMD measured at the hip and spine
increased in joggers (1.3%) and weightlifters (1.2%) compared with controls,
but the increase at the hip did not reach statistical significance.27 Similar
site specific increases have been reported in young male rowers. In a
controlled study of 17 novice rowers, spine BMD increased by 2.9% after seven
months of training.28
Chow and colleagues randomised 48 healthy
postmenopausal women to a control group, aerobic exercise group, or a strength
training group for one year.29 Compliance
at the exercise classes was 70% and at the end of the programme both exercise
groups had significantly greater bone mass than controls. However, there was no
significant difference between the aerobic and strength trained groups. In an
elegant study of 56 postmenopausal women, subjects were randomised to either
high repetition, low load (endurance) or high load and low repetition
(strength) training groups for one year.30 Significant
gains in BMD compared with the control limb were seen at the hip and radius in
the strength group, but only at the radius in the endurance group. It seems
likely that peak load rather than number of repetitions is the more important
factor in achieving bone gain.
Nelson and co-workers studied the effect of
a high intensity strength training programme on femoral and lumbar BMD.31 Significant
increases were seen at both sites in the exercise group, with a fall in BMD
seen in the control group. The differences in BMD were independent of change in
diet and significant changes also occurred in muscle mass and strength. Similar
findings were reported by Lohman and colleagues from a programme of
weightlifting in premenopausal women.32 They
found a significant increase in lumbar spine BMD after 18 months (3%–6%),
noting that the major change in BMD took place after the first five months of
exercise (2.8%). High intensity strength training can significantly increase
High impact exercise of increasing
intensity in healthy premenopausal women leads to significant increases in hip
BMD compared with controls.33 A
significant increase of 1.6% in femoral neck BMD was seen in the exercise group
compared with a reduction in BMD in controls (−0.6%) The effect was site
specific and there were no differences at non-weightbearing sites. Bassey and
Ramsdale report a similar effect in premenopausal women after six months of
high impact (jumping and skipping) activity compared with controls whose
exercise was low impact only.34 Using
a crossover study design, they demonstrated a similar increase in the control
group in response to high impact activity. Strength training with
non-weightbearing exercises does not appear to lead to an increase in BMD.35,36
Regular brisk walking can maintain BMD in
previously sedentary postmenopausal women. In a prospective randomised
controlled trial over 12 months, BMD at the spine and calcaneum decreased in
the control group but small increases were seen in the walking group with the
differences reaching statistical significance at the calcaneum.37 There
has been one randomised controlled trial of a “home based” exercise programme
in postmenopausal women.38 Women
in the exercise group were asked to flex each hip 60 times two or three times
each day with a 5 kg bag on the knee and changes in BMD were measured at the
lumbar spine. On an intention to treat basis there was no significant benefit
from exercise. However, on subgroup analysis subjects who exercised assiduously
lost significantly less bone than controls.
Most intervention studies have attempted to
increase BMD at specific sites by careful targeting of the exercise. Only one
randomised study has demonstrated any significant systemic effects of exercise
on bone density.15 In
postmenopausal women there was a significant difference in the cross sectional
area of the radius after a three year walking programme, although loss of BMD
was similar in both groups.
A number of studies have demonstrated
significant gains in BMD in individuals with osteoporosis. In an open study of
postmenopausal women with a fractured forearm, patients were asked to squeeze a
tennis ball three times a day for six weeks using their uninjured arm.39 Muscle
strength improved significantly and bone mineral content also increased
significantly as a result of exercise. Significant improvements in bone mass
can also occur as a result of low impact exercise at the lumbar spine of women
referred with established osteoporosis.40 Similar
benefits have been reported in women with low BMD who have taken part in
strength training.41,42 Iwamoto et
al in a randomised controlled trial also found that high impact
exercise increased BMD. However continued exercise was required to maintain any
There are two randomised controlled trial
of exercise in corticosteroid induced osteoporosis. In the first, 16 male heart
transplant recipients after transplantation were randomised to strength
training or control groups. However after six months of exercise, BMD in the
exercise group had increased significantly towards pretransplant levels but BMD
in controls remained unchanged from values two months after transplant.44 In
the other trial, low impact training in patients with Crohn’s disease who were
compliant with the programme, lead to an increase in BMD at the hip (see box 1).45
Box 1: Example of exercises involved
in home based low impact exercise programme 45
- Five minute warm-up consisting of general whole body pulse
raising and mobility promoting activities, followed by preparatory
stretching of the main muscles being worked in the core programme.
- Core programme of low impact exercises:
- Box step
- Heel presses
- Upper body twists
- Cross steps
- Knee lift triangles
- Stomach exercise-shoulder lifting off floor while on back
- Rowing action
- Bent side leg raise
- Bent leg raise
- Front leg tucks
- Side leg presses
- Exercise regimen needs to be taught by suitably qualified
- Regular face to face contact with supervising professional
- Level of intensity at start depends on capabilities of
- Intensity of exercise increased by increasing the number of
repetitions and increasing resistance to movement.
- Exercise regimen needs to be undertaken at least twice per
OPTIMUM TYPE AND FREQUENCY OF EXERCISE
The duration, intensity, frequency, and
optimum type of physical activity for increasing BMD and reducing fracture risk
has not been determined. However, invasive studies of controlled local loading
in animal models suggest that the effective osteogenic forces are at the top
end of the range normally experienced, are rapid in onset, and unusual in their
strain pattern.46 Population
studies involving athletes indicate that high impact sports such as running,
squash, and weightlifting lead to an increase in BMD, whereas low impact sports
such as swimming do not.18–22 Intervention
studies also suggest that high impact activities are better at increasing BMD
than low impact activities. Low impact activities only seem to help prevent
further loss.26,27,34 Other
reviewers have concurred with this view.47
Compliance with exercise regimens is a very
important factor in trying to increase BMD and changing sedentary lifestyles is
very difficult.38 Three
intervention studies have successfully shown that previously sedentary
individuals could increase their activity levels. They shared a number of
features—(i) home based, (ii) unsupervised informal sessions, (iii) frequent
professional contact, (iv) walking as the promoted exercise, and (v) exercise
of moderate intensity and lesser frequency—that were associated with higher
participation. Continued exercise is also important in maintaining previous
gains in BMD, otherwise bone loss recurs and previous gains are lost.
No intervention study has assessed the
effect of exercise on the rate of osteoporotic fracture. The evidence for
exercise having a protective role against hip fracture comes from large
epidemiological studies. Paganini-Hill and colleagues, in a study from the USA,
reported an odds ratio of 0.3 for hip fracture in women who had a high
frequency of participation in outdoor sports, compared with those with a low
frequency of participation.48 A
similar risk reduction has been reported in studies from Britain49 and
Hong Kong.50 Cooper
and colleagues in the UK found a significantly reduced risk of hip fracture in
individuals who were physically active for more than five hours a week.49 Kujala et
al in Finland found that vigorous exercise provided a similar
protective effect for osteoporotic hip fracture.51
Cross sectional studies have shown a
positive correlation between bone mineral density (BMD) and exercise.
Intervention studies suggest that high impact exercises are better at
increasing BMD (table 1). The effect is site specific. Uptake and continued
compliance is crucial to any intervention in the form of exercise on BMD. It is
the opinion of the authors that exercise should be encouraged in those at risk
of osteoporosis and those with osteoporosis, along with other life style
measures (adequate calcium intake, stopping smoking, modest alcohol
consumption, and maintaining an adequate body weight). Exercise has important
additional benefits, such as increased muscle strength and coordination, which
decrease the risk of trauma leading to osteoporotic fractures. Exercise also
has other benefits, which are important for the general wellbeing of
patients—for example, decreasing cardiovascular disease, decreasing the risk of
diabetes, and helping depression.
Different forms of exercise and their
impact on BMD
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