Leisure-time physical activity, body mass index, and waist circumreference : a longitudinal twin study from adolescence to adulthood

ABSTRACT LEISURE-TIME PHYSICAL ACTIVITY, BODY MASS INDEX, AND WAIST CIRCUMFERENCE: A LONGITUDINAL TWIN STUDY FROM ADOLESCENCE TO ADULTHOOD Minna Kujala Master’s Thesis of Sport Medicine The University of Jyväskylä The Faculty of Sport and Health Sciences Department of Health Sciences 2010 Pages: 54, 8 appendixes The aim of this study was to investigate the effects of persistence and changes in the frequency of leisure- time physical activity on body mass index and waist circumference from adolescence to adulthood. Also, this study investigates the effect of the intensity of physical activity on body mass index (BMI) and waist circumference in adulthood. Participants in the study, members of the Finn-Twin 16 study cohort (N=6084), answered study questionnaires between 1991 and 1995 at age 16 and later at age 17, 18.5, and 24, about the frequency and intensity of their leisure-time physical activity, body height, and weight. Participants also measured their waist circumference at a mean age of 24. One question with seven alternative responses probed the stability of participants’ leisure-time physical activity outside school. Another question with four alternative responses probed the intensity of that leisure-time physical activity. This study concludes that a high total frequency and intensity of leisure-time physical activity results in smaller BMI growth from adolescence to adulthood and in a smaller waist circumference at a mean age of 24. Physically inactive boys had larger BMI increases than boys participating very frequently in physical activity, while physically inactive girls had larger BMI increases than girls participating in high intensity physical activity. This study also concludes that at a mean age of 24, the waist circumference of boys and girls who participate in vigorous physical activity is smaller than the waist circumference of those who participate in very light, light, or moderate physical activity. On the basis of earlier studies and on the results of this study, we can conclude that the intensity of physical activity and a high level of physical activity frequency may play an important role in reducing the growth of a person’s BMI from adolescence to adulthood and in reducing waist circumference growth in adulthood. Reducing the growth of BMI and waist circumference is known to lower the risk of metabolic syndrome and cardiovascular diseases. Key words: physical activity, twins, body mass index, waist circumference, adolescents, longitudinal study