PT Classroom - The Effects of Exercise on Bone Mass Density in Prepubertal Females: Short and Long-Term Effects ׀ by Jennifer Hill, MPT, CSCS

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


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.

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