Author

Beth Gluck

Date of Award

5-2004

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Food Science and Human Nutrition

Advisor

Susan Sullivan

Second Committee Member

Richard Cook

Third Committee Member

Phillip Pratt

Abstract

Research on physical activity has reported a link between weight-bearing activity and increased bone mass. Strengthening the bones earlier in life may decrease the risk of osteoporosis later in life. This study was designed to investigate the relationship between physical activity and bone density in adolescent girls who were participants of a larger Seasonal Bone Study (SBS) conducted by the Department of Food Science and Human Nutrition at the University of Maine. A total of twenty-three adolescent girls between the ages of 9 and 14 completed the three-year study. The SBS began in September 2000 and was completed in September 2003. Each subject kept four days of activity records (three weekdays and one weekend day) every six months, each winter and summer. The activity data was collected throughout the study by an interviewer administered telephone conversation on the day following the record keeping. The activity data collected biannually from the subjects was categorized into three different levels of activity by the subjects. These categories were minutes spent sitting, minutes spent in low intensity activity and minutes spent in high intensity activity. Additional data collected from the subjects biannually were bone mineral density (BMD) measurements, height, weight, age and date of puberty. Subjects were also questioned about time spent in extracurricular physical activity. The primary outcome measure was the bone mineral density each six months September 2000 and September 2003 (six 6-month periods in total). The measures of physical activity were the four-day averages of minutes spent sitting, in low intensity activity and in high intensity activity each six months, along with the average hours per week spent in extracurricular weight bearing activities. There was no positive correlation found between BMD at each visit and the fourday averages of activity classified by intensity. BMD was significantly correlated with minutes spent sitting for September 2002, indicating that the girls who sat the most had higher BMDs. There were significant correlations between age, weight, height, and BMI and BMD. After controlling for maturational age, height, and weight, there was a significant correlation found between weight-bearing extracurricular physical activity and BMD post menarche. There was also a significant correlation between height and weight and BMD, showing that these both play a strong role in determining bone mineral density. Age and BMI no longer correlated with BMD after correcting for maturational age. In conclusion, time spent in weight-bearing extracurricular physical activity was shown to be positively related to BMD after controlling for maturational age, height, and weight. Therefore, the results indicate that weightbearing activity during puberty may contribute to stronger and denser bones. More research is needed with an increased number of subjects in order to more accurately investigate the effects of physical activity on bone mineral density during puberty. Additionally, this study found that a relatively easy way to obtain measure of physical activity level, such as asking questions regarding hours spent in extracurricular activity, is a good indicator of influence of physical activity on bone. The diary method in combination with characterization of physical activity into three categories was not specific enough to separate subjects based on impact of activity on bone. By encouraging physical activity during puberty, positive effects on the bone may be achieved.

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