Self-reported physical activity and bone mineral density in urban adolescent girls

This observational study aimed to examine the prevalence of activities of daily living, as well as the impact of leisure time activities, on bone mineral density in urban adolescent girls.

Patients completed a 23-item physical activity questionnaire at baseline, recording time spent in various activities in the previous 7 days. In addition to leisure time activities, activities of daily life were also considered. Activities were characterized and scored by metabolic intensity (METPA) and mechanical strain on bone (MECHPA). The METPA score for each activity is the product of the metabolic intensity of the activity and the time spent in the activity. The MECHPA score estimates the mechanical strain on bone from ground reaction forces. The logged scores were divided into quartiles with the lowest quartile as the reference group.

Four hundred fifty-five females (ages 12-18 years) completed the survey (62% black and 38% non-black). The log of the overall METPA score was a significant predictor of bone mineral density (i.e. higher METPA score predicted a higher bone mineral density, P = 0.03). A MECHPA score in the highest quartile was associated with a higher bone mineral density (P < 0.05) when compared to the other MECHPA quartiles.

In this population of urban adolescent girls, activities of daily living were reported with a higher frequency than sports activities. Results indicated a positive association between the time spent in metabolically intense activities and bone mineral density. There also appears to be a threshold effect for the relationship between activities with the highest mechanical strain and bone mineral density.