Effects of a School-Based Physical Activity Intervention on 24-Hour Movement Behaviours and Motor Development in Preschool Children - Study Protocol

BACKGROUND AND RATIONALE

Physical activity, sedentary behaviour, and sleep operate as a constrained, interdependent 24-hour composition: time reallocated to one behaviour necessarily displaces another. This integrated perspective underpins the WHO 24-hour movement guidelines for children under 5 years, which recommend at least 180 minutes per day of total physical activity (including at least 60 minutes of MVPA), limited sedentary screen time, and adequate sleep duration (WHO, 2019). Despite clear guidance, adherence is critically low. A large-scale systematic review across 23 countries found that only a small proportion of young children meet all three components simultaneously (Tapia-Serrano et al., 2022). In Portugal, accelerometer-based evidence from the PRESTYLE study showed that only 4.5% of preschool children met the combined 24-hour recommendations, with particularly low compliance for physical activity and screen-time thresholds (Vale \& Mota, 2020). Movement behaviour patterns formed in the preschool period show tracking into later childhood, with potential cumulative effects on health and learning trajectories.

From a developmental standpoint, early childhood is a sensitive period for the maturation of motor competence, executive functions, and socioemotional self-regulation. Motor competence is not only an outcome in its own right but a plausible mechanism linking physical activity exposure to broader developmental gains (Logan et al., 2015). Emerging evidence from compositional data analysis supports the premise that reallocating time away from sedentary behaviour towards physical activity and sleep is associated with more favourable cognitive and behavioural outcomes in preschool-aged children (Li et al., 2024; Xu et al., 2025). The SuperQuinas programme has demonstrated beneficial effects on motor competence and physical activity in primary school populations in Portugal (Costa et al., 2024; Rodrigues et al., 2025); however, its effectiveness in preschool-aged children has not yet been examined.

STUDY DESIGN

The study adopts a school-based, quasi-experimental, parallel-group, class-clustered controlled design. It is conducted at a single public preschool in Maia, northern Portugal (Gandra Basic School, Águas Santas School Cluster). Four intact preschool classes of approximately 20 children each (total N approximately 80) are allocated at the class level, with two classes assigned to the intervention condition and two to the control condition. Non-random class-level allocation was adopted due to organisational and pedagogical constraints inherent to the school context. All four classes receive an identical weekly dose of curricular Physical Education delivered by a qualified PE teacher. Baseline equivalence between conditions is formally assessed for all demographic and outcome variables, and observed imbalances are addressed through covariate adjustment in the primary analyses.

INTERVENTION

The experimental condition receives one additional 60-minute structured physical activity session per week for 12 consecutive weeks, delivered by the principal investigator during regular school hours. The programme adopts a play-based, child-centred approach integrating locomotor, object control, and stability tasks within activities that are developmentally appropriate for children aged 3 to 6 years. Task complexity, movement demands, and instructional cues are progressively adjusted across the intervention period to account for age-related differences in coordination, attentional capacity, and cognitive flexibility.

Each session follows a standardised three-phase structure. The session opens with a brief warm-up of exploratory movement and dynamic play to prepare children physically and cognitively. The central phase consists of structured motor activities and games designed to elicit sustained MVPA and repeated practice of key motor patterns; these activities frequently incorporate rule-based elements and inhibitory control demands, embedding cognitive stimulation within the physical tasks. The session closes with a short cool-down of low-intensity movement and guided reflection reinforcing positive movement behaviours. Each session also includes age-appropriate health messages delivered informally through storytelling and playful interaction, addressing the importance of physical activity, reduced sedentary time, and consistent sleep routines. The additional SuperQuinas session does not replace existing curricular PE but is added to the weekly schedule, increasing total structured physical activity exposure without reducing time allocated to other curricular areas.

Intervention fidelity is monitored through structured session checklists completed by the principal investigator after each session, documenting adherence to the planned structure, deviations, and child engagement. Individual attendance is recorded per session. Children attending fewer than 75% of sessions (fewer than 9 out of 12) are classified as low-adherence participants and included in the intention-to-treat primary analysis but excluded from the pre-specified per-protocol sensitivity analysis.

CONTROL CONDITION

Children allocated to the control condition continue exclusively with regular curricular Physical Education, delivered by a qualified PE teacher following national educational guidelines. No additional physical activity sessions, educational materials, or behaviour change strategies are introduced in control classes during the study period. The content, duration, and pedagogical focus of control-condition PE sessions are documented descriptively through consultation with teaching staff to contextualise intervention effects. At study completion, control classes are offered access to the SuperQuinas in Preschool materials and guidance.

PROCESS EVALUATION

A process evaluation is conducted alongside the outcome evaluation following the Medical Research Council framework for process evaluation of complex interventions (Moore et al., 2015). Three dimensions are monitored throughout the intervention period. Fidelity is assessed through structured session checklists completed after each of the 12 weekly sessions. Dose is quantified through individual attendance records, enabling calculation of per-participant intervention exposure. Acceptability is assessed through structured field notes capturing child engagement, motivation, and teacher feedback after each session. Process evaluation data are reported alongside primary outcome results to enable transparent assessment of implementation quality.

STATISTICAL ANALYSIS

The primary analytical framework uses longitudinal linear mixed-effects models under an intention-to-treat principle, with participants analysed according to their allocated condition regardless of attendance or compliance. Models include fixed effects for time (T0, T1, T2, T3), condition (intervention vs. control), and a time by condition interaction term as the primary test of intervention effect, with adjustment for baseline outcome values, age in months, and sex. Given the small number of clusters (four classes), class-level clustering is addressed through robust clustered standard errors. Missing data are handled using full-information maximum likelihood estimation under the missing-at-random assumption. A pre-specified per-protocol sensitivity analysis is conducted excluding low-adherence participants. For 24-hour movement behaviour data, exploratory compositional data analysis using isometric log-ratio coordinates is conducted to examine shifts in time-use profiles as compositions, complementing the univariate modelling approach.

• Cognitive Competence [Time frame: Assessed at four time points: baseline (T0, Week 0), mid-intervention (T1, Week 6), post-intervention (T2, Week 12), and follow-up (T3, Week 24).]
• Socioemotional Regulation [Time frame: Assessed at four time points: baseline (T0, Week 0), mid-intervention (T1, Week 6), post-intervention (T2, Week 12), and follow-up (T3, Week 24).]