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Researchers at Wright State University School of Medicine in Ohio, U.S.A., have found that leisure activity has a significant impact on the rate of bone mass increase in both girls and boys. Lead author Miryoung Lee and colleague followed a group of 99 children, aged 8 to 18, to determine how changes in physical activity affects their bone mineral density, a measure of bone strength. For both sexes, the rate of bone accumulation was found to be higher with increasing leisure activity level (see conference Abstract No. P191).
In girls, more intense physical activity that is associated with sports also leads to greater increases in bone density. Similar effects were not seen in boys taking part in sports. "During childhood and adolescence, children's bodies grow rapidly and bone mass is accumulated quickly. The amount of bone built during adolescence and early adulthood is one of the most important factors related to the risk of developing osteoporosis in later years. These findings confirm that physical activity is important for optimal bone accrual during childhood, consequently leading to higher peak bone mass," said Lee.
The researchers also found that for an average follow-up period of four years, physical activity levels were not significantly different between boys and girls. "It is, however, more important for girls to exercise during childhood because they are at greater risk of osteoporosis later in life," Lee said.
Finnish study corroborates exercise benefits in building strong bones
Researchers from Finland also emphasized how important it is to not only start but maintain regular exercise. Marjo Lehtonen-Veromaa and colleagues at Turku University Central Hospital, found that over a period of four years, girls who stopped exercising had a much lower increase in bone content than those who maintained their physical activity (see conference Abstract No. P673).
At six month intervals for three years, and then once again after seven years, Lehtonen-Veromaa recorded physical activity among 142 girls. The researchers also measured the bone mineral content of the thigh bone and lumbar spine at the start of the study and at the three, and seven year time points. They found that the third of the girls who exercised most had the highest increase in thigh bone mineral content over the seven years (24 percent increase). In the third of girls who exercised the least, that increase was only about 16 percent.
During the course of the study, physical activity among 30 of the girls fell by more than 50 percent and by 25-50 percent in another 29 girls. The researchers found that the effect of this reduction in activity was pronounced. In the 30 girls who were exercising the least by the end of the study, bone mineral content of both the thigh and the lumbar spine were significantly lower than in the girls who maintained their level of physical activity. This effect was more pronounced at the thigh bone.
"It is understandable that girls who exercised intensively during the prepubertal period are disposed to change their exercise habits a few years later, since the objects of their interest will change easily during puberty," said Lehtonen-Veromaa. She suggests that if young girls get tired of one kind of physical exercise, they should search, either by themselves or with their parents, for another type of physical activity that may be interesting enough to pursue. "It is of great importance to continue a physically active way of living because it seems to be deleterious for bone health if the magnitude of physical activity descends deeply, added Lehtonen-Veromaa.
Brazilian study shows benefits of exercise
And in keeping with current theories that bone built up during ones youth puts one in good stead when older, Fernando Siqueira and colleagues from the Federal University of Pelotas, Brazil, reported that exercise in childhood and adolescence can reduce the risk for late life osteoporosis (see conference Abstract No. P260). Siqueira and colleagues questioned over 1,000 individuals aged 50 and over in southern Brazil and matched their osteoporosis history with their history of physical activity between ages 10 and 19, as judged from an internationally recognized physical activity questionnaire.
Sigueira and colleagues found that those volunteers who were active in adolescence had a 45 percent lower risk for osteoporosis.
Recognizing the importance of exercise for bone health, World Osteoporosis Day 2005 was dedicated to the theme Move it or lose it. The IOF published "Move it or Lose it," a guide to how exercise benefits bones of all ages. Part of our "Invest in Your Bones" series, the guide explains how exercise helps to build and maintain strong bones, helps prevent falls and fractures, and speeds rehabilitation. Copies can be found on the IOF website.