Age
Age is the one of the main factors believed to determine levels of integrated movement
behaviours in children and adolescents. There is a decline in PA level with age,
confirmed by cross-sectional studies and longitudinal studies (150-155). For example,
a cross-sectional study in Canada that included (n=401) children aged from (8-13 years
of age) and measured daily MVPA and VPA by actiGraph accelerometer over seven
consecutive days found that levels of PA decreased with increasing chronological age
(151). A recent longitudinal cohort study in United Kingdom (UK) (Gateshead
Millennium Study) with 8 years of follow-up included 545 children and measured
habitual MVPA objectively by ActiGraph GT1M accelerometer first at 7 years of age,
and then at 9, 12 years of age. This study reported there was a decline in levels of PA
across the eight years, with evidence that the total volume of PA had started declining
by age 7 years (156).
Several studies have confirmed that time spent in sitting and screen based activity was
higher in adolescents compared to young children (157). Increasing age was associated
with more prolonged sitting bouts with fewer breaks in sitting. Strong recent evidence
comes from a longitudinal analysis of the Gateshead Millennium Study cohort in the
UK in 2016 with eight years follow up as noted above - in this study ST increased with
chronological age from 7 to 15 years of age and this increase in ST displaced time
spent in PA; median ST increased from 51% of waking hours at 7 years to 74% at 15
years of age, with sedentary fragmentation decreasing from 7 years to 15 years as
Duration of sleep is also age-dependent as noted above: preschool-age children had
longer sleep durations than school-age children (earlier bed time and later wake-up
time), while children at school age and older had less sleep duration as they had later
sleep onset time with unchanged wake-up time. Waking time appears more stable
perhaps because of the need to wake-up early to go to school (118).
Sex
Sex is a second important determinant of levels of integrated movement behaviours in
children and adolescents. Boys are more active compared to girls of the same age,
confirmed by both cross-sectional studies and longitudinal studies (151-156). For
instance, evidence comes from the Lifestyle of our Kids (LOOK) longitudinal study,
which included 276 boys and 279 girls from 29 schools aged 8-12 years of age. PA
was measured using pedometers (Walk 4 Life, Plainfield, IL, USA) over seven
consecutive days and the results revealed that, level of PA was lower in girls compared
to boys and girls were 19% less active than boys (159).
Similarly, on average girls accumulate higher ST than boys (67, 101, 157, 160).
Interestingly, an observational cross-sectional survey within the framework of the
ENERGY-project (EuropeaN Energy balance Research to prevent excessive weight
Gain among Youth) that included 686 children aged 10-12 year of age, 53% girls,
across 5 European countries using accelerometers to determine the amount of ST again
found that ST was higher in girls and girls spent significantly more time sedentary
There is only limited evidence that sleep duration and timing are influenced by gender,
at present. In the French Mother–Child Cohort (EDEN Study) cross-sectional study
factors associated with short sleep duration 1028 child (boys (n=546) and girls
(n=482)) aged 3 years of age, were investigated by using parent report. This study
found that, boys had significantly shorter sleep duration compared to girls as boys had
later bedtimes and earlier wake‐up times than girls. However, the mean total sleep duration, if the time naps were included, did not differ significantly by gender (162).
Sleep duration guidelines are not gender-specific at present (131-133).
Season
Lastly, some studies confirm that there is seasonal effect on at least some of the 24
hour movement behaviours in at least some parts of the world. Seasons are defined as
the natural periods in which the year is divided, which vary by weather conditions,
daylight hours and temperature (163). A systematic review included 37 primary
studies with a total of 291,883 children and adolescents (140,482 male and 152,085
female) from eight different countries to explore the effect of season, and consequently
weather, on levels of PA, and they revealed that, level of PA varies with season (163).
Further, boys had different PA patterns as they tended to be more sedentary and less
active during the winter, while girls had more consistent levels of PA and ST across
the seasons. A pilot study in 24 participants aged 10-13 years characterised seasonal
variation in MVPA and ST. They found that, participants were more active in the
summer and activity levels were higher after school than in school and ST was higher
At present, there is limited evidence that sleep duration and timing are influenced by
seasons in children and youth. A recent cross-sectional analysis of 669 participants
aged at age’s 12–14years, used wrist accelerometers to assess the sleep timing,
duration and quality with season and daily weather conditions. They found that season
was associated with large changes in sleep timing but not with sleep duration. Sleep onset time was 41 minutes later in summer and 28 minutes earlier in spring and autumn compared to winter and that indicating seasonal variation in the timing of the sleep period (165).
In summary, these three factors – age, sex and season - are amongst the most important
confounding influences in studies 24-hour movement behaviours in children. Thus,
investigators need to consider these three factors (age, gender, time of year) when
designing studies to consider variation in or differences in 24-hour movement
behaviours between groups.