Reliable method to estimate characteristics of sleep and physical inactivity in free-living conditions using accelerometry

PURPOSE: The purpose of this study is to use a new method to assess the characteristics of sleep and diurnal physical inactivity in human beings by means of accelerometry, noninvasively and in free-living conditions. METHODS: Forty girls and 40 boys aged 13 to 15 years, randomly selected from rural Senegal, wore an accelerometer for a 72-hour period during the dry season in 1998 and 2000. An algorithm already tested in another study was used to objectively calculate the characteristics of sleep and physical inactivity from movement registration provided by accelerometry. RESULTS: Adolescent girls slept for a longer time and more quietly than adolescent boys (8 hours 45 minutes versus 8 hours 9 minutes). Girls were more inactive than boys (4 hours 23 minutes versus 2 hours 49 minutes). Reliability estimates of physical inactivity period measures were excellent (0.74 to 0.78), and those of sleep period and length measures were acceptable (0.45 to 0.61). Girls and boys had the same levels of reliability, except for sleep efficiency measures. CONCLUSIONS: These findings could be explained by the nature and sex division of habitual tasks within the community. The accelerometer is a valid and useful epidemiologic tool for measuring characteristics of sleep and physical inactivity in free-living conditions. This innovative tool opens new prospects in epidemiology and public health, especially in the worldwide epidemic of chronic diseases associated with physical inactivity and sleep disorders.