The research team, led by Heidi J. Syväoja of Likes and Jamk University of Applied Sciences in Jyväskylä, drew on data from two completed Finnish studies. A total of 253 children with an average age of 9.5 years and 174 adolescents averaging 13.7 years provided complete data on their daily movement patterns and their basic academic skills. Hip-worn ActiGraph accelerometers tracked each participant’s waking hours for seven consecutive days, capturing time spent sedentary, in light physical activity, in moderate activity, and in vigorous activity. Because accelerometers are notoriously poor at registering activities such as swimming and cycling, the students also kept diaries, and the time they reported for these activities was added into the moderate-intensity category. Sleep duration came from self-reported bedtimes and wake-up times across six nights.

Academic performance was measured with standardized, age-appropriate tests administered in schools by trained research assistants. The children completed the online FUNA battery, which probes arithmetic reasoning, single-digit and multi-digit calculation under tight time limits, along with a sentence-reading fluency test adapted from the Woodcock-Johnson task in which students judge whether statements like blueberries are green are true or false against the clock. The adolescents tackled the pen-and-paper Basic Arithmetic Test, solving as many mixed operations as possible in three minutes, and the ALLU reading test, in which students match pictures to phonologically similar words under time pressure. Scores were standardized against Finnish reference samples so that results could be compared within each age group.

The genuinely novel element lies in the statistical approach. Sleep, sedentary time, light activity, moderate activity, and vigorous activity together consume the entire day, so an increase in any one behavior necessarily means less time for the others. Conventional regression methods, which treat each behavior as an independent variable, cannot capture this constraint. Compositional data analysis, or CoDA, borrowed from geology and chemistry, can. Using isometric log-ratio transformations, the researchers converted the five-part daily composition into linearly independent predictors, each expressing one behavior relative to the geometric mean of the others. These ratios then entered linear mixed-effects models, adjusted for age, gender, special educational needs, body fat percentage, and parental education, with school classes modeled as random intercepts to account for the clustered data structure.

Among children, one association stood out from an otherwise quiet field. Time spent in light physical activity, relative to all other behaviors, was inversely associated with reading fluency, with a standardized coefficient of negative 0.98 and a p-value of 0.014. No other behavior, whether sleep, moderate activity, vigorous activity, or sedentary time, showed a significant relationship with reading or arithmetic fluency in children. Among adolescents, none of the five behaviors predicted either academic outcome on its own, although the composition as a whole approached significance in some models. The behavior variables added between 0.007 and 0.024 units to the models’ marginal R-squared, and in the children’s reading model the improvement was statistically significant according to a Wald test.

The adolescent data harbored a subtler and arguably more intriguing finding: gender moderated the link between sedentary time and reading fluency. The interaction between gender and sedentary time was statistically significant, with a coefficient of negative 2.85 and a p-value of 0.037. Interpreted together with the main effects, this indicates that more sedentary time was associated with better reading fluency in both boys and girls, but the association was considerably stronger among boys. No such gender moderation appeared for arithmetic fluency, and no other movement behavior interacted with gender in either age group.

To translate these statistical patterns into practical terms, the team ran theoretical thirty-minute reallocation scenarios, swapping half an hour of one behavior for another within the fixed twenty-four-hour budget. For children, none of these hypothetical substitutions produced changes that differed significantly from the sample average, suggesting that no single thirty-minute trade-off dramatically alters a young child’s fluency scores. For adolescents, however, the picture was more differentiated. Moving thirty minutes from sedentary time into sleep or moderate activity, or from light activity into sleep, appeared to widen the reading gap between girls and boys, with predicted gains for girls and predicted losses for boys. Girls outperform boys in reading fluency on average, so the reallocation scenarios suggest that these swaps would amplify an existing disparity rather than close it.

Why would more light activity be linked to worse reading, and more sitting to better reading, particularly among boys? The authors argue that light activity is unlikely to be harmful in itself. Instead, hours spent in low-level movement, the countless transitions and errands of daily life, displace time from behaviors known to support learning: sufficient sleep, vigorous exercise, and, crucially, reading itself. Reading fluency develops through reading, which requires stillness and sustained concentration and therefore accumulates as sedentary time. When fluency is weak, reading becomes less automatized and demands greater attentional resources and executive control, creating a potential feedback loop in which poor readers read less, and read less fluently as a result.

The absence of an association between movement behaviors and arithmetic fluency is also instructive. The tests used here measured basic arithmetic, the rapid retrieval and execution of simple calculations, rather than the more cognitively demanding tasks of applying and reasoning that previous research has linked to the attentional and executive benefits of exercise. It is plausible that physical activity matters most for mathematics when tasks strain working memory and cognitive flexibility, not when they tap overlearned procedures. There is also a measurement wrinkle: self-reported physical activity has often shown positive associations with academic performance, while accelerometer-measured activity has not, possibly because hip-worn devices miss coordinative, skill-based movements such as cycling, swimming, and agility activities that may be the most cognitively engaging.

The study’s limitations warrant care in interpretation. Its cross-sectional design captures a single moment in time and cannot establish whether movement patterns cause differences in fluency or vice versa. Sleep was self-reported, the analytic samples came from more educated families and showed better academic performance and higher activity than excluded participants, and the two age groups were assessed with different instruments, limiting direct comparability. Still, the study is among the first to apply compositional data analysis to the full twenty-four-hour movement spectrum in relation to academic skills, and one of the few to extend this framework to adolescents older than twelve. Its broader message is a corrective to simple prescriptions. From a whole-day perspective, supporting reading fluency may require strategies tailored to age and gender: for children, protecting sleep, adequate moderate-to-vigorous activity, and regular reading exposure, while recognizing that light activity competes for the same finite hours; for adolescents, acknowledging that some sedentary time devoted to reading appears beneficial, and that the optimal balance of sleep, movement, and stillness may look different for boys than for girls.

Subject of Research: Associations between 24-hour movement behavior composition and academic performance in children and adolescents

Article Title: 24-hour movement behaviors in association with academic performance in children and adolescents: cross-sectional compositional data analysis

Article References: Syväoja, H. J., Kukko, T., Asunta, P., Hakonen, H., Kulmala, J., Lerkkanen, M.-K., Räsänen, P., & Tammelin, T. H. (2026). 24-hour movement behaviors in association with academic performance in children and adolescents: cross-sectional compositional data analysis. Journal of Activity, Sedentary and Sleep Behaviors, 5(1), Article 8. https://doi.org/10.1186/s44167-026-00099-x

Image Credits: AI Generated

DOI: 10.1186/s44167-026-00099-x

Keywords: physical activity, sedentary behavior, sleep, academic performance, reading fluency, arithmetic fluency, children, adolescents, compositional data analysis, accelerometry, gender differences, Finland