1 Physical activity characteristics of adolescents at the baseline of a weight management trial

Purpose of study Measurement of physical activity (PA) using wrist worn monitors is becoming more widely accepted due to commercial availability and increased wear time compliance over waist worn monitors. Little research is available to describe adolescent PA measured at the wrist. The objective of this study is to describe the PA characteristics of a sample of high school students as measured by GENEActiv accelerometers placed at the wrist. Methods used In 2014 and 2015, 878 students in the 9th and 10th grades at 8 New Mexico high schools wore an accelerometer for at least 4 days. These accelerometer records were evaluated to determine average daily minutes of sedentary, light, moderate, and vigorous activity using a method developed for use in children. A multilevel mixed effects generalised linear model was used to compare average minutes of PA by sex and weight status. Repeated measures were used for day of the week comparison. Summary of results 50.9% of subjects met PA guidelines of >60 min of moderate to vigorous PA (MVPA) per day. Our data shows a difference in vigorous minutes between weight categories but no significant difference in MVPA minutes. Students with a BMI ≥95 th percentile did 5 min of vigorous activity while students with a BMI <85 th percentile did 7 min (p<0.001). Friday was the most active day of the week, with an average MVPA of 65 min and Sunday was the least active with 45 min of MVPA. Male subjects had an average MVPA of 69 min per day while female subjects had an average of 59 min per day. Conclusions MVPA estimates were higher than previously reported in other studies, possibly due to the placement of the accelerometer on the wrist vs waist in this study. Interventions for increasing PA and managing weight in adolescents may benefit from focusing on increasing weekend PA and increasing MVPA among girls. More information about the relationship between amount and timing of vigorous activity and health outcomes is needed.