Due to the recent and increasing evidence of the adverse effects of sedentary behaviors in adults, accurate and valid measures of the full range of sedentary behaviors are clearly beneficial for all populations . This research has directly examined sedentary levels of adolescent females and has described the patterns of accumulation over 24-hours on weekdays and weekend days and across the school day. For the first time, an accelerometer based inclinometer, which has been recommended [1, 11], was used to describe these sedentary patterns. A description of the methodology used to analyze ActivPAL output was also presented in the hopes of illuminating the intricate patterns of an activity as ubiquitous as sedentary behavior. Patterns have been looked at in greater detail, in 5 minute blocks, as recommended by past studies which have simply broken down the day by hour . The use of these methodologies can easily be employed when examining sedentary behaviors in all populations, in the hopes of closing the gaps in objectively describing the sedentary profiles of free-living populations.
Analysis from a representative sample of the United States population  and a cross-section of 9 European countries  highlighted older adolescents as a particularly sedentary group. Similarly, results reported in other objective examinations of sedentary behavior in adolescent populations found the majority of the waking day and the full 24-hour day were spent sedentary [8, 42–44]. The results of the present study are consistent with these findings. Aside from television viewing habits, little is known about the pattern of sedentary behavior in adolescents across weekdays and weekend days. Jago et al found that adolescent females spent differing number of minutes per hour sedentary throughout weekdays and weekend days with no definite trend obvious . As adolescents engage in high levels of volitional sedentary pastimes  one may assume adolescents to be more sedentary in their own leisure time, at evenings and on weekends (when they had the freedom to choose these sedentary pastimes). Participants spent similar amounts of time sedentary on both weekdays and weekends, unlike results from previous research on younger adolescent females  and children . However, the present data indicated that these adolescent females were sedentary in longer more continuous bouts on weekdays compared to weekend days. No evidence exists yet to say that these longer bouts have a deleterious effect on young people's health. Sedentary behaviours in general can have an adverse effect on current body composition  and may track into adulthood  which in turn can increase the risk of coronary heart disease and other co-morbidities , and intuitively should be discouraged.
Our findings also highlight the school day (9 am-3 pm) as a particularly sedentary time for this population. To our knowledge, this is the first study to objectively report the manner in which adolescents accumulate their sedentary time while at school using a direct measure of posture. Steele et al. reported that 8-10 year old children accumulate 242 minutes of sedentary time during school based hours and this was not different to out of school sedentary time . Regardless of any differences between school and after school, unwittingly, the school setting appears to promote unbroken continuous periods of sitting; periods which have potential deleterious effects on health in adulthood . Our results indicate that while there was no difference in the volume of sedentary time, these adolescent females broke up their sedentary periods more outside of school rather than during school which is encouraging. The duration of each classroom based lesson in these schools ranged from 25 to 40 minutes, resulting in students sitting, uninterrupted, for these lengths over many classes for the majority of each day. School-based interventions which have the primary goal of decreasing sitting time and which have a sedentary message that is independent of other health behavior messages (e.g. physical activity) are lacking  and warranted  in the literature. We have identified times of day when adolescent females are particularly sedentary and have given a magnitude to the amount of sitting/lying that is done which can inform interventional design. While it may not always be feasible to reduce total sedentary time during school, identifying these typical or 'usual' unbroken bouts offer an easier or more acceptable approach for school-based sedentary interventions.
Inclinometer based measures of sedentary time, such as the ActivPAL, provides researchers with a real time, accurate and objective measure of sedentary behavior, providing actual inclination information as it occurs. More researchers are turning to these direct and objective methods due to the lowering costs of these devices, coupled with the rich and descriptive output obtained, such as the data that has been presented herein. The utility of methodologies using the ActivPAL can be best evaluated and understood when they are compared with the existing published methods of examining sedentary levels and patterns which have already been mentioned in the Background. In highlighting the limitations of past studies, the limitations of the present study also need to be considered. Although this was a random, cross-sectional sample, the size of the sample suggests the results must be interpreted with caution. The results are also descriptive in nature and may not be extended to other populations or age groups at this stage. We have presented total sitting/lying time over the full 24-hour day, but without a self-report log for participants to report at what time they got up and went to bed, we cannot make any conclusions on total time spent sitting during waking hours to compare with past studies. This value for 24-hour sedentary time will be higher than previous studies not only because it includes time spent sedentary after a participant goes to bed but also includes time spent lying (not just sitting time) during waking hours. While this does make comparisons with past accelerometer results difficult, it gives a total value for sedentary, including time spent lying down during the day and night, for this group of adolescent females. Also, the absence of accurate health markers does not allow conclusions on the relationship with sedentary patterns and behavior to be drawn. However, these results do give a more detailed insight into the patterns of sedentary behavior of adolescent females. The limitations of the sample should not detract from the presentation of rich, detailed information that can be garnered from an objective device such as the ActivPAL. Continuous data such as this, combined with robust physiological and health measures, could begin to identify whether a health-compromising level of sedentary time exists.