Gamified Versus Regular Exercise Snacks on Stationary Bikes, as One 10-Minute or Two 5-Minute Sessions a Day, for Children in an Inclusive Primary School

• Stationary cycling with game display (Behavioral): Riding a stationary exercise bike whose screen shows a video game.
• Stationary cycling with regular display (Behavioral): Riding the same bike with the screen showing only a timer, pedaling rate and heart rate, with no game elements.
• One 10-minute ride per riding day (Behavioral): One 10-minute ride per riding day on 3 fixed school days a week for 8 weeks.
• Two 5-minute rides per riding day (Behavioral): Two 5-minute rides per riding day, about 3 to 5 hours apart, giving the same daily total as the one-ride schedule.

Primary outcomes

• Distance per scheduled minute (km/min) recorded by the stationary-bike software on each riding day [Up to 8 weeks]: Sum of distance (km) recorded across all study rides on a scheduled riding day, divided by the 10-minute daily budget. Both displays run the same virtual track so the distance algorithm is identical. Refused rides scored 0; days not offered or absent excluded from the denominator; lost measurements treated as missing. Higher values indicate more riding output.

Secondary outcomes

• Mean heart rate (beats per minute) in the last 60 seconds of each ride, measured by an arm-worn optical heart-rate sensor [Up to 8 weeks]: Mean of sensor readings over the final 60 s, also as % of age-predicted maximum (208 - 0.7 × age). Rides included only if sensor coverage ≥ 80% with no gap > 60 s. Higher values indicate higher intensity.
• Minutes per riding day in the target heart-rate zone, measured by an arm-worn optical heart-rate sensor [Up to 8 weeks]: Minutes with heart rate between 60% and 80% of age-predicted maximum, summed across rides on a riding day; range 0-10. Used to compare received intensity between one 10-min ride and two 5-min rides.
• Affect during the ride, measured by the Feeling Scale [Up to 8 weeks]: Single-item Feeling Scale (Hardy \& Rejeski, 1989), -5 (very bad) to +5 (very good), reported by pointing to a pictorial card at minute 5 of a 10-min ride and minute 2.5 of each 5-min ride. Higher scores indicate more positive affect.
• Affect after the ride, measured by the Feeling Scale [Up to 8 weeks]: Single-item Feeling Scale, -5 (very bad) to +5 (very good), completed privately on a tablet. Higher scores indicate more positive affect.
• Post-ride enjoyment score on a study-specific 0-10 numeric rating item [Up to 8 weeks]: "How much did you like this ride", 0 (not at all) to 10 (very much). Higher scores indicate greater enjoyment.
• Perceived exertion after the ride, measured by the OMNI Bike Scale for children [Up to 8 weeks]: Perceived exertion is assessed within 5 minutes after each ride using the OMNI Bike Scale for children (Robertson et al., 2000), a pictorial 0-10 scale showing a child cycling up an increasingly steep hill. Scores range from 0 (extremely easy) to 10 (extremely hard). Higher scores indicate greater perceived exertion. The scale is presented on a tablet with the standard pictorial anchors and Chinese translations of the verbal anchors; children respond by pointing or tapping, with the item read aloud by study staff if needed.
• Perceived competence and perceived pressure scores on two study-specific 0-10 numeric rating items [Up to 8 weeks]: Competence: "How well did you ride today", 0-10, higher = greater competence. Pressure: "Did you feel pushed to ride", 0-10, higher = greater pressure. Reported separately.
• Proportion of intervals on-task in a 20-minute classroom window after riding, measured by momentary time sampling by blinded observers [Up to 8 weeks]: Proportion (0-1) of 10-s intervals coded on-task in the classroom window beginning at 14:05 on each riding day, and at 10:40 on two-ride days, for riders who rode that day and their waitlist classmates. Fixed observer pool unaware of allocation and display; 20% of windows double-coded. Higher = more on-task.
• Percentage of scheduled riding opportunities offered, attended, refused, stopped early and completed, from the study attendance log [Up to 8 weeks]: Offered and attended use all scheduled opportunities as denominator; refused, stopped early and completed use offered-and-present opportunities. Unit: %.
• Percentage of rides rated more enjoyable, about the same, or less enjoyable than the previous ride, on a study-specific three-category item [Up to 8 weeks]: Three categories; reported as % of rides in each category by display and schedule. Not applicable on the first ride; on two-ride days "previous ride" is the earlier ride that day.
• Change in exercise motivation measured by the Behavioural Regulation in Exercise Questionnaire-2, children's version (C-BREQ-2) [Baseline and week 9]: 18 items in five subscales (amotivation, external, introjected, identified, intrinsic regulation), each item scored 0 (not true for me) to 4 (very true for me); subscale score is the item mean (0-4). Higher intrinsic and identified scores indicate more autonomous motivation (better); higher amotivation and external scores indicate less autonomous motivation (worse).
• Change in health-related quality of life measured by the KIDSCREEN-10 Index [Baseline and week 9]: 10 items scored 1-5, sum 10-50 converted to T-score (mean 50, SD 10). Higher = better. Pilot estimate, riding vs waitlist.
• Change in inhibitory control measured by the Flanker task reverse-coded reaction-time interference score [Baseline and week 9]: A computerised Flanker task administered on a tablet (PsyToolkit). For each participant, mean reaction time (milliseconds) is computed for correct congruent and incongruent trials; the reverse-coded interference score is mean congruent minus mean incongruent reaction time, so that higher scores indicate better inhibitory control. Accuracy (%) is reported alongside.
• Facial Expression Valence Index From Camera-Based Facial Expression Recognition [Up to 8 weeks]: percentage points, calculated for each ride as the percentage of valid camera samples classified as happy minus the percentage classified as sad, angry, fearful, disgusted or contemptuous; range -100 to 100, with higher values indicating more positive facial expression. Measurement tool: camera-based facial expression recognition system mounted above the bike screen, which classifies each sample of the rider's face as neutral, happy, sad, angry, surprised, fearful, disgusted or contemptuous; only these classifications are stored. The percentage of samples in each category is also reported.

Other outcomes

• Number of adverse events and serious adverse events from the study safety log [Up to 8 weeks]: Counts by type.

Sex: All, ages: 6 Years to 15 Years, accepts healthy volunteers

Inclusion Criteria:

* Student in Primary 4 to 6 at the participating school
* Written informed consent from a parent or legal guardian and the student's own assent; students with special educational needs use a pictorial assent procedure
* Completed parental health screening questionnaire
* Tall enough to pedal normally with the seat at its lowest position, checked during a trial ride
* Able to complete 5-minute and 10-minute rides and brief self-ratings with verbal or visual prompts

Exclusion Criteria:

* Heart, lung or metabolic disease diagnosed by a physician that requires restriction of physical activity
* History of photosensitive epilepsy, or seizures of unknown cause
* Lower-limb injury or surgery in the past 3 months that affects pedaling
* Unable to get on and off the bike safely, as judged by the physical education teacher and the inclusive-education coordinator