Wendy Kohrt, Ph.D., reviewed the work of the
musculoskeletal health subcommittee. The group researched the following 6
questions and came to the associated conclusions:
Is there evidence that physical activity reduces the incidence
of osteoporotic fractures?
There is evidence from prospective cohort and case-control studies for an
inverse association between physical activity and fracture risk, particularly
for hip fractures.
The evidence also supports a dose-response relationship between physical
activity and fracture risk, such that a greater volume of physical activity
confers greater risk reduction.
There was discussion among the subcommittee as to whether there is actual
scientific evidence to support the notion that physical activity reduces the
risk of bone fracture. The subcommittee will need to review the precise
wording of the statement as to whether it can say there is "some" evidence
that supports their position.
From the studies that were reviewed which included 11 prospective cohort, 1
retrospective cohort, 6 case-controlled, 1 RCT and 2 cross-sectional studies,
all supported an association of physical activity with reduced risk. The
limitation of the data is that the studies do not isolate physical activity as
the sole cause for risk reduction. The evidence is most consistent in hip
fracture risk; however, less consistent evidence in other fractures should not
be considered as evidence that physical activity plays a reduced role in these
fractures. Studies that isolated sex were consistent but studies with mixed
sex groups were less consistent.
The data demonstrates, based on different exposures of activity, that bone
fracture risk is reduced by 36 – 41%. Higher levels of physical activity
showed a risk reduction of 36 – 68%. Standing 40 hours or more a week was
associated with a 34% reduction; however, one cannot discriminate volume
versus intensity. There is evidence that decreases in activity increase risk.
Is there evidence that physical activity reduces the risk for osteoporosis
by increasing or slowing the decline in bone mass density (BMD)?
Exercise training can increase, or attenuate the decrease, in BMD at clinically
relevant skeletal sites. The magnitude of the effect is approximately 1-2% per
year for studies up to 1 year in duration. Both weight bearing endurance
training (ET) and resistance training (RT) can be effective in this area.
The evidence base for this question included 15 meta-analyses of which 4 found
no significant effects on BMD. 10 of the 13 reports showed significant changes
in LS BMD. 2 of 8 reported changes in FN BMD. 3 of 6 reported significant
changes in BMD of any hip region. 4 of 5 studies found significant effects of
exercise on BMD in premenopausal women as opposed to 10 of 12 studies showing
significant effects in postmenopausal women. Meta-analysis of studies of men
appeared to find larger effects of exercise on BMD than observed in men.
Regarding type of exercise there were significant effects on LS and hip BMD in
ET. Walking only meta-analysis found effect on LS but not FN BMD. 3 out of 4
studies found significant effects on LS BMD in RT. There were no significant
effects on FN or other hip regions.
There is no evidence from meta-analyses for dose response effects. One
relatively large RCT on resistance training found a positive association of
total weight lifted with change in BMD.
Is there evidence that physical activity reduces or increases the
incidence of OA?
In the absence of major joint injury, there is no evidence that regular moderate
activity increases the risk of developing OA. There is also little evidence to
suggest that low to moderate levels of physical activity may provide limited
protection against the development of OA.
Certain groups may have a moderately elevated risk of OA as a result of
participation in high-impact activities and long-term participation. There may
also be additive effects of recreational and occupational physical activity on
OA, for occupations that require excessive knee bending, kneeling, or twisting/torsional
Females may have increased risk of physical activity related OA. Individuals
with excessive body mass may have risk of OA but some evidence suggests that
physical activity does not augment that risk. Previous joint injuries are a
risk factor for OA but it is not clear if activity further increases the risk.
Is there evidence that physical activity is harmful or beneficial for
adults with OA or other rheumatic conditions?
There is clear evidence that participation in both endurance and resistance
types of exercise provide disease-specific benefits for persons with OA
without exacerbating symptoms or worsening disease progression. Patients with
OA should pursue activities that are relatively low impact, not painful, and
do not have a high risk of joint injury. The data suggests that a prescription
of 30 minutes per day for 5 days per week is appropriate.
Is there evidence that physical activity increases or preserves muscle
mass throughout the lifespan?
Is there evidence that physical activity improves skeletal muscle quality,
defined as changes in intrinsic or extrinsic force-generating capacity?
Specific modes and intensities of activity can preserve or increase skeletal
muscle mass, strength, power, and intrinsic neuromuscular activation. Benefits
appear to be similar in women and men and pervasive across the lifespan. Regular
and progressive high-intensity RT can increase muscle size, strength, power and
neuromuscular function. Endurance types of activity do not increase muscle mass
or quality, but may attenuate the rate of loss with aging. Muscle quantity and
quality are not closely linked with a specific health outcome, but are important
components of physical fitness. There is strong evidence that progressive,
high-intensity RT can increase muscle mass and strength in a dose-dependent
manner and are similar in both men and women. There is also evidence that both
RT and ET results in improvements in muscle strength.
For question 6 the evidence suggests muscle power may play a more important role
in physical function and fall prevention than muscle strength.