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Fractures
associated with osteoporosis are a major health problem among the
elderly. A principle cause of these fractures is a reduced bone
mass, which can be the result of age-related bone loss and/or
failure to achieve sufficient peak mass at maturity (1). Exercise
may contribute to the prevention of osteoporosis and fractures by
increasing the amount of bone accrued during growth, by reducing the
menopause-related and age-related bone loss, and/or restoring bone
already lost in the elderly (2). Besides the genetic component that
influences both the overall growth pattern and osteotropic endocrine
system, physical activity has been shown to be strongly associated
with high bone mass density (BMD) (3).
The crucial years during which these external forces can
substantially affect bone mass accumulation has been shown to occur
between early childhood and late adolescence, during the period of
maximal linear growth in females (4). In females, many studies have
concluded that the greatest gains in BMD occur in the prepubertal
stage, between the ages of 11-15 (1,3,4,6,7). In order to reduce
fracture risk later in life, the gains in BMD must be shown to be
sustained in adulthood, despite changes in activity levels. The BMD
gains from exercise during adolescence have been shown to be
valuable in terms of fracture risk reduction (2). Therefore, the
greater responsiveness of the growing skeleton is likely to provide
a lasting residual benefit in adulthood (2). This means a decrease
in the risk of osteoporosis and associated fractures.
Physical Therapists have an important role in prevention of
osteoporosis and the associated complications. Patients must be
educated regarding the great importance of exercise on proper
skeletal health. The proper exercise guidelines must be addressed as
well as the proper use of exercise equipment, proper body mechanics,
variety in the exercise program, and the awareness of warning signs
of overuse injuries (5). In designing rehabilitation programs, it is
essential for physical therapists to be knowledgeable on age-related
bone physiology and pathology.
Extensive research has been performed to analyze the effects of
exercise on BMD in adolescent females. Slemenda el at. (7) found
significant increases in BMD during prepubescence. Ninety children,
aged 6-14, completed a 3-year randomized clinical trial that
examined the effects of physical activity, calcium supplementation,
and sexual maturation on rates of gain in skeletal BMD. Physical
activity was estimated by means of questionnaires to children and
their mothers. Activity data was collected for both weight-bearing
and non-weight-bearing activities. Increases in BMD were found in
the prepubertal females, and the most significant predictor of BMD
at all skeletal sites was regular weight-bearing physical activity
(7). These findings are consistent with other findings; however, I
believe the authors tried to examine too many BMD contributing
factors simultaneously. Indeed these factors do occur
simultaneously, but control is needed to isolate these variables in
order to draw specific conclusions. Also, the method of utilizing a
questionnaire to monitor physical activity may be inaccurate and
incomplete.
In another study, Bass (2) and colleagues quantified gains in BMD at
various stages in order to examine lasting effects. Bass et al (2)
conducted a study with 45 active prepubertal female gymnasts and 35
prepubertal controls as well as 36 retires elite gymnasts and 15
adult controls. In the cross-sectional analysis, areal BMD in the
active gymnasts was higher than controls. During 12 months of
follow-up, the actual increase in total body, spine, and leg areal
BMD was 30-85% more rapid in the active gymnasts that in the matched
controls. In the retired gymnasts and adult controls, areal BMD was
6-16% higher in the gymnasts at all sites, except the skull and did
not diminish with increasing duration since retirement. The authors
explain that bias is unlikely to explain the higher areal BMD
because 1) the Z score above the predicted mean increased with
increasing duration of training, with the regression line passing
through zero, 2) there was site specificity, and 3) the longitudinal
data support the cross-sectional data. Thus, this study provides
consistent evidence that exercise before puberty may increase BMD
and these gains are shown to be maintained into adulthood (2). The
authors suggest that the increments achieved by vigorous exercise
during prepubertal years are large and likely to reduce fracture
risk 2-to4-fold (2). The greater responsiveness of the growing
skeleton is likely to provide a lasting residual benefit in
adulthood despite the lower frequency and intensity of exercise. In
terms of methodology, this study may be limited by using only
aerobic, weight bearing activities; the researchers did not look at
the effects of other types of training. Also, females who are young
athletes may have a greater tendency to be active adults due to
their upbringing as an active individual. Therefore, one may wish to
analyze the lasting effects of BMD from an active adolescence to a
sedentary adulthood.
More research is needed to draw conclusions between prepubertal
exercise and both active and sedentary adult lifestyles. Studies are
needed to determine the mechanisms responsible for the greater
responsiveness of the growing (modeling) skeleton to exercise and
the maintenance of the benefits into adulthood, despite less
intensive exercise. In researching exercise, specific information on
parameters such as intensity, frequency, duration, and type of
exercise should be addressed. This information will provide physical
therapists additional knowledge necessary for optimal exercise
prescription and patient education.
In conclusion, research supports the idea that exercise may increase
BMD in females. These changes may be of most benefit during the
optimal growth window in female adolescence. By utilizing exercise
to increase BMD during the time when bone growth is at its peak,
residual benefits are likely to ensue. These benefits not only
improve the structure and function of human bone tissue, but also
may be likely to significantly reduce the likelihood of osteoporosis
and associated disorders. Physical therapists play a key role in
educating females on proper bone health and in designing exercise
programs for patients that will maximize benefits.
Last revised: August 12, 2010
by Jennifer Hill, MPT, CSCS
References
1) Recker R, Davies K, Hinders S, Heaney R, Stegman M, Kimmel D. Bone Gain
in Young Women. JAMA. 1992;268:2403-2408
2) Bass S, Pearce G, Bradney M, Hendrich E, Delmas P, Harding A, Seeman E.
Exercise Before Puberty May confer Residual Benefits in bone Density in
Adulthood: Studies in Active Prepubertal and Retired Gymnasts. J Bone Min
Res. 1998;13:500-507
3) Theintz G, Buchs B, Rizzoli R, Slosman D, Clavien H, Sizonenko P, Bonjour
J. Longitudianl Monitoring of Bone Mass Accumulation in Healthy Adolescents:
Evidence for Marked Reduction after 16 years of age at the Levels of Lumbar
Spine and Femoral Neck in Female Subjects. J Clin Endocrin Metab.
1992;75:1060-1065.
4) Bonjour J, Theintz G, Buchs B, Slosman D, Rizzoli R. Critical Years and
Stages of Puberty for Spinal and Femoral Bone Mass Accumulation during
Adolescence. J Clin Endocrin Metab. 1991;73:555-563
5) Goodman C, Boissonnault W. Pathology: Implications for the Physical
Therapist. Philadelphia: W.B Saunders Company. 1998;617-621.
6) Haapasalo H, Kannus P, Sievanen H, Heinonen A, Oja P, Vuori I. Long-term
Unilateral Loading and Bone Mineral Density and Content in Female Squash
Players. Calcif Tussue Int. 1994;54:249-255.
7) Slemenda C, Reister T, Hui S, Miller J, Christian J, Johnston C.
Influences on Skeletal Mineralization in Children and Adolescents: Evidence
for varying Effects of Sexual Maturation and Physical Activity. J Peds.
1994;125:201-207. |
