Breaks in Sedentary Time during Childhood and Adolescence: Iowa Bone Development Study

KWON, S., T. L. BURNS, S. M. LEVY, and K. F. JANZ. Breaks in Sedentary Time during Childhood and Adolescence: Iowa Bone Development Study. Med. Sci. Sports Exerc., Vol. 44, No. 6, pp. 1075-1080, 2012. Purpose: The frequency of interruptions in sedentary time (sedentary breaks) is an aspect of sedentary behaviors that may be associated with metabolic health outcomes. The aim of this study was to describe the change in the frequency of sedentary breaks during a 10-yr period from ages 5 to 15 yr. Methods: The longitudinal Iowa Bone Development Study has collected accelerometry data at approximately 5, 8, 11, 13, and 15 yr. Data from participants who wore an accelerometer at least 10 h.d(-1) and 3 d per data collection episode were used (423 children at age 5 yr, 550 children at age 8 yr, 520 children at age 11 yr, 454 children at age 13 yr, and 344 children at age 15 yr). The frequency of sedentary breaks was determined based on accelerometry data and compared by weekday/weekend, period during the day, gender, and data collection episode. Results: The frequency of sedentary breaks decreased by >200 times per day during a 10-yr period from ages 5 to 15 yr. Linear regression models estimated a 1.84-times-per-hour decrease per year for boys and a 2.04-times-per-hour decrease per year for girls (P values < 0.0001). Both boys and girls showed significantly fewer breaks on weekdays from, morning to 3:00 p.m. than on weekends from morning to 3:00 p.m. (P values < 0.0001). The frequency of sedentary breaks was slightly higher among boys than among girls (gender difference <= 2 times per hour, P values < 0.01 at ages 11, 13, and 15 yr). Conclusions: Breaks in sedentary time notably decrease during childhood and adolescence. During school hours, boys and girls have fewer breaks in sedentary time than during any other period of weekday or weekend day.