The technical foundation of the study is the accelerometer itself. Participants in both waves wore these small motion-sensing devices, typically secured at the hip or wrist, which record raw acceleration hundreds of times per second. Sophisticated filtering algorithms then translate that continuous stream into categories: sedentary time, meaning sitting or lying still; light physical activity, the gentle movements of daily life such as walking slowly or doing chores; and moderate-to-vigorous physical activity, the breathless, sweat-inducing exertion that health guidelines target. Unlike questionnaires, which are notoriously unreliable in children who struggle to estimate their own activity, accelerometers capture what actually happens, minute by minute, across entire weeks.

The sample comprised 1,043 young people in the 2014-15 wave and 790 in 2022-23, each contributing valid measurement days to the analysis. The researchers applied design-based statistical tests — t-tests and Kruskal-Wallis tests weighted to reflect the survey’s complex sampling design — to compare time spent in each activity category between survey years, and ran the analysis separately for weekdays and weekend days, for three age bands, and for boys and girls. This stratification matters because averages can conceal opposing trends: a national mean that looks stable might hide improvement in one group and deterioration in another.

That is precisely what the data revealed. Weekday sedentary time showed no significant change in any group, a finding the authors present as evidence that the school-day structure — with its scheduled lessons, breaks and commutes — anchors young people’s sitting patterns regardless of the year. But weekend sedentary time told a different story. Adolescents aged 10 to 13 increased their weekend sitting by 23 minutes per day, a statistically significant rise, and boys in that same age band showed an even larger increase of 40 minutes per day, which fell just short of conventional significance thresholds. Girls aged 5 to 9 added 24 minutes of weekend sedentary time per day, also significant. These are not trivial amounts: forty extra minutes of daily sitting, accumulated across weekends over years of childhood, represents a substantial shift in energy balance and metabolic exposure during developmental years.

The activity side of the ledger brought one genuinely encouraging result. Girls’ weekday light physical activity rose by 16 minutes per day and their moderate-to-vigorous activity by 6 minutes per day, both statistically significant improvements. On weekend days, girls showed a further non-significant uptick of 4 minutes in moderate-to-vigorous activity. Boys, by contrast, were essentially flat: their activity levels remained stable across the eight-year span, with one exception — boys aged 10 to 13 showed a non-significant decline of 22 minutes per day in weekend light activity, hinting that the same group accumulating extra sitting time may be losing gentle, everyday movement in exchange.

Against the headline metric that public health authorities care most about — adherence to international guidelines — the picture was one of stubborn stagnation. The guidelines require an average of at least 60 minutes of moderate-to-vigorous physical activity per day, plus vigorous activity on at least three days per week. In 2014-15, 37.6 percent of Belgian young people met this standard; by 2022-23 the figure was 39.9 percent, a change the study classifies as stable. Roughly three in five children and adolescents still fail to reach the minimum activity level associated with cardiometabolic health, bone development and psychological wellbeing — a shortfall unchanged across a period that included a global pandemic and its attendant lockdowns.

One subgroup showed a trend worth watching. Among girls, estimated guideline adherence climbed from 23.4 percent to 30.4 percent — a seven-point gain that, remarkably, did not reach statistical significance, with a p-value of 0.072. The near-miss illustrates a recurring tension in survey research: a seven-percentage-point improvement in a national sample is potentially meaningful for public health, but with 790 participants in the later wave, the study lacked the statistical power to rule out chance. The authors are careful not to overclaim, noting only that the difference fell short of significance, and their conclusion emphasises continued surveillance rather than declared victory.

The pandemic context deserves attention when interpreting these numbers. The 2022-23 wave captured young people whose formative years overlapped with COVID-19 restrictions, school closures and the wholesale migration of social life onto screens — conditions that many studies elsewhere linked to sharp drops in youth activity. That the Belgian data show stability on weekdays and only selective weekend deterioration suggests either resilience in the underlying habits, partial recovery after the acute restriction period, or genuine continuity in how Belgian children structure their time. The study design cannot separate these explanations, but the fact that weekday patterns survived the interval intact is itself informative: the rhythms imposed by school appear to buffer children against broader societal drift toward sedentary living.

What emerges from the full analysis is a portrait of stasis with fault lines. The overall stability conceals a gender divergence — girls improving, boys flat — and an age-specific weekend problem concentrated in the 10-to-13 bracket, the years surrounding puberty when independent screen use typically expands and supervised sport often contracts. The authors’ stated conclusion is measured: despite some favourable changes, most participants did not meet physical activity guidelines, highlighting the need for continued surveillance and targeted interventions. In a European public health landscape where youth inactivity is implicated in rising childhood metabolic disease, the Belgian dataset offers something rare — a like-for-like, sensor-verified comparison spanning eight years — and its message is that without deliberate intervention, the default trajectory of childhood weekends is toward the chair.

Subject of Research: Accelerometer-measured changes in physical activity and sedentary time among Belgian children and adolescents between 2014-15 and 2022-23

Article Title: Changes in accelerometer-measured physical activity and sedentary time among young people in Belgium between 2014-15 and 2022-23

Article References: Thérésa, L., Vicka, V., & Nicolas, B. (2026). Changes in accelerometer-measured physical activity and sedentary time among young people in Belgium between 2014-15 and 2022-23. Scientific Reports. https://doi.org/10.1038/s41598-026-76969-w

Image Credits: AI Generated

DOI: 10.1038/s41598-026-76969-w

Keywords: physical activity, sedentary time, accelerometers, children, adolescents, Belgium, public health, temporal trends, exercise guidelines, Scientific Reports, epidemiology, screen time