December 6 - 7, 2007 Advisory Committee Meeting
Musculoskeletal Health Subcommittee Report
Wendy Kohrt, Ph.D., opened the report on musculoskeletal health.
Dr. Kohrt thanked the members of the subcommittee, Miriam Nelson, Jennifer
Hootman, Roger Fielding, Nancy Lane and CDC liaisons, David Brown and Jesus
Soares. The subcommittee outlined six questions, all of which start with the
preface, "is there evidence that physical activity does something?"
With respect to bone, does physical activity reduce the
incidence of osteoporotic fractures?
Does physical activity reduce the risk for osteoporosis by
increasing or perhaps slowing the decline in bone mineral density?
Does physical activity increase or preserve muscle mass
throughout the life span?
Does physical activity improve skeletal muscle quality?
Does physical activity reduce or increase the incidence of
Does physical activity have any benefits to individuals with
osteoarthritis and other rheumatic conditions?
Dr. Kohrt proceeded in addressing whether physical activity
reduces the incidence of osteoporotic fractures? This question was studied
through the review of 11 prospective, one retrospective cohort studies, six case
controls, one small randomized control trial, a follow-up to a randomized
control trial, and two cross-sectional comparisons. In looking at all the
different study designs and results there does seem to be enough evidence to
support an association between physical activity and reduced fracture risk.
However, a limitation of the data is that it does not isolate physical activity
as causal in fracture reduction.
Hip fractures are the most frequently examined fracture and the
studies are consistent in the beneficial effects of physical activity to reduced
hip fracture. From a global skeletal perspective the methods for measuring
physical activity may not be adequately capturing or characterizing the
potential site specificity of skeletal benefits. It is easier to report a
conclusion on a site specific part of the skeleton.
The next issue addressed was sex specificity. The data available
included eight women only studies, and surprisingly only five men only studies.
All of the studies on women reported a favorable association as well as all the
studies on men. Less consistent were the studies that included both men and
women. Part of the differences found in combined sex studies may have to do with
the different methods of categorizing physical activity.
From a dose-response perspective, both the qualitative and
quantitative approaches for discriminating physical activity exposure support an
inverse association of level of physical activity with fracture risk, indicating
more activity supports better bone health. None of the studies allowed for any
conclusions on volume of exercise or intensity.
Dr. Kohrt next addressed the question of whether there is
evidence that physical activity reduces the risk of osteoporosis by increasing
or perhaps slowing the decline in bone mineral density. Initial conclusions do
support that exercise training can attenuate the decrease in bone mineral
density. The magnitude of the effect is approximately 1% - 2%. Both endurance
training and resistance training can be effective. Long term effects are not yet
known. Finally, there is no evidence that has emerged to support a dose-response
Dr. Kohrt introduced Jennifer Hootman who reviewed the evidence
on the relationship between physical activity and the reduction of incidence of
osteoarthritis and whether physical activity had any benefit to people with
osteoarthritis. The group's initial impression is that, in the absence of major
joint injury, there is no evidence that regular, moderate or vigorous physical
activity increases the risk of osteoarthritis nor does it provide any benefits
to individuals that currently have a rheumatic condition. There is moderate
evidence that light to moderate activity may be protective for knee and hip
osteoarthritis, particularly among women. From the CDC database 35 studies were
identified of which 12 were observational, 6 case control and 6 were cohort
studies. The self-report studies can be seen as obtained through members of the
general population. The control or cohort studies can generally be seen as
dealing with elite athletic populations. The studies dealing with elite athletes
do show increased incidences of rheumatic conditions but one can conclude the
increased incidence from high-level intensity training.
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