Weight-Bearing Activities May Be Best to Promote Healthy Bone Mass in Adolescent Females

Regular physical activity has been shown to influence good bone health throughout life and has shown promise as a means of prevention and intervention for osteoporosis. Recent data suggests that bone may be most responsive to the stimulus of weight-bearing exercise during the early childhood growth periods, according to a study presented at the American Academy of Orthopaedic Surgeons' (AAOS) 70th Annual Meeting in New Orleans.

Osteoporosis is a progressively degenerative bone disease resulting in reduced bone mineral density (BMD) and bone mass and increased susceptibility to fractures. Osteoporosis and low bone mass are major public health threats in the United States. It has been estimated that 50% of Caucasian women will suffer an osteoporotic fracture in their lifetime. Previous studies have shown that BMD is the single most important factor related to the occurrence of osteoporosis and related fractures. One of the strongest risk factors for future osteoporotic fractures is low BMD and its measurement can be used, in combination with other risk factors, to identify groups at high risk for developing osteoporosis.

The purpose of this study was to compare bone mineral densities of adolescent females involved in sports with varying magnitudes of skeletal loading,or weight-bearing activity. Weight-bearing describes any activity you do on your feet that works your bones and muscles against gravity. With weight-bearing exercise, bone adapts to the impact of weight and pull of muscle by building more cells and becoming stronger.

Of the three groups studied, Olympic style weight lifting, competition-level swimming and competition-level tennis, the resulting data support the concept that the loading stresses of weight-bearing activities such as weight lifting and tennis may facilitate bone accrual in adolescent females to adult levels sooner than in a non weight-bearing activity such as swimming. "During childhood, when bone accrual is greatest, exercise potentiates bone development. In addition, the data resulting from this study indicate that certain types of exercise may affect bone mass. For example, various activities such as stair climbing, step aerobics, soccer, jogging and skating are weight-bearing activities that may increase bone mass sooner than expected in adolescents and to a greater degree than we thought," says Dr. Laura Gehrig, principal study investigator and orthopaedic surgeon at Louisiana State University Health Sciences Center in Shreveport, Louisiana.

The study consisted of 62 females between the ages of 8 and 17 who participated in weight lifting, tennis or swimming. Athletes who trained at least 5 hours per week, at least 10 months of the year and who have been in their sport for at least a year were included in the study. Bone densities for each subject were recorded from the right heel of each subject using a portable densitometer. This allows accurate assessment of BMD with a low radiation exposure, making it suitable for use in children. BMD data was collected and compared with normative values for BMD from the World Health Organization for adult females 20-45 years of age. When the mean BMD of each group was compared to the normative values from WHO for adult females, the BMD of the swimmers was significantly less (p<.001), while the mean BMD of the weight lifters and tennis players were not significantly different (p=.103 and .101).

The 26,047-member American Academy of Orthopaedic Surgeons (www.aaos.org ) or ( http://orthoinfo.aaos.org ) is a not-for-profit organization that provides education programs for orthopaedic surgeons, allied health professionals and the public. An advocate for improved patient care, the Academy is participating in the Bone and Joint Decade (http://www.usbjd.org ), the global initiative in the years 2002-2011 to raise awareness of musculoskeletal health, stimulate research and improve people's quality of life. President Bush has declared the years 2002-2011 National Bone and Joint Decade in support of these objectives. The Academy's Annual Meeting is being held February 5-9, 2003, at the Ernest N. Morial Convention Center.