Physical Activity, Sedentary Behaviour and Sleep in Adolescent Females in New Zealand

Abstract

Background: Physical inactivity, sedentary lifestyles, obesity, and their associations with numerous adverse health outcomes are arguably the largest health concerns to children and youth. Historically, moderate-to-vigorous intensity physical activity (MVPA) is most commonly assessed in relation to health. However, physical activity is often the smallest component of 24 h activity, which includes light-intensity physical activity (LPA), sleep and sedentary behaviour (SB). New research suggests these activities in combination rather than isolation may help researchers better understand the health of specific populations, therefore potentially aiding the development of effective public health interventions.

Objective: The purpose of this study was to describe the 24 h activity patterns: sleep, sedentary behaviour, and light and moderate-to-vigorous intensity physical activity, measured in adolescent females of the SuNDiAL project.

Design: Adolescent females aged 15-18 y were recruited from 8 locations in New Zealand (NZ). Actigraph GT3X+ accelerometers and self-report wear-time diaries were used to identify time in sedentary pursuits, light-intensity physical activity, and moderate- to-vigorous intensity physical activity. Type and intensity of physical activity was determined using cut-points by Freedson, Melanson, and Sirard (1998). Sleep duration was identified using the Sadeh, Sharkey, and Carskadon (1994) algorithm constrained using self-reported bed-times from the daily sleep log.

Results: Participants spent half their time sedentary (50%), one-third sleeping (31%), 15% in LPA, and 4% in MVPA. On average, participants spent 49.1 minutes per day in MVPA, and 7.3 h per day sleeping. Approximately 23% and 27% of participants met the guidelines for sleep and MVPA, respectively. Those in the healthy body mass index (BMI) category were more likely to meet the guidelines than their overweight and obese counterparts. Time spent sedentary did not appear to differ across weight categories; however, overweight and obese participants spent less time in MVPA and sleep and more time in LPA.

Conclusion: Female adolescents spend the majority of their time sedentary. Approximately one in four meet either the sleep guidelines (8-10 h per day) or the physical activity guidelines (>60 min per day), and one in ten participants met both guidelines. These findings indicate the poor behavioural choices of this population and the need for more targeted effective public health interventions.

Keywords: physical activity, adolescent, sedentary behaviour, 24-hour activity, sleep.