The effect of a one-year vigorous physical activity intervention on fitness, cognitive performance and mental health in young adolescents: the Fit to Study cluster randomised controlled trial
Wassenaar TM, Wheatley CM, Beale N, Nichols T, Salvan P, Meaney A, Atherton K, Diaz-Ordaz K, Dawes H, Johansen-Berg H · 2021
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Sample
18,261 randomised (104 schools); 16,017 pupils / 93 schools at baseline form the ITT analysis sample
Population
18,261 pupils aged 12-13, 104 UK state secondary schools (field setting)
Design
Cluster RCT: 104 English secondary schools randomised 52/52, 18,261 Year 8 pupils. Intervention added ~10 min HIIT-style vigorous PA per PE lesson (4-min warm-up burst + three 2-min infusions per hour of PE) for one academic year. Primary outcome maths attainment, prospectively registered (ISRCTN15730512, Mar 2017) and independently evaluated by NatCen/EEF; the secondary outcomes reported in THIS paper (fitness, executive function latent variable, relational memory, processing speed, mental health) were RETROSPECTIVELY registered (ClinicalTrials.gov NCT03286725, 18 Sep 2017, after the intervention began) and analysed by the trial team, who co-developed the intervention. Attrition is severe: 11 schools withdrew before baseline (analyses restricted to 93 schools / 16,017 pupils), 24 more schools lost to follow-up, and at post-test only ~51% completed the fitness test, ~39% a cognitive task and ~14% everything. ITT run on multiply imputed data; complete-case sensitivity analyses agree.
Key findings
The largest school PA RCT: null on every outcome including the fitness mediator itself, and null on mental health. Fidelity caveat, stated precisely: of the 22 intervention schools that reported, 17 (77%) said they delivered the intervention in >=50% of PE lessons but only 2 (9%) in >90% — which is 17 of the 52 originally randomised intervention schools (33%), and the paper's own summary is "fewer than half the schools in the intervention group managed to deliver the intervention in at least 50% of PE lessons". Objectively measured vigorous PA did not differ significantly (full lesson 3.65 vs 3.09 min/hour, p=0.23; active lesson 4.91 vs 4.38, p=0.07). Crucially the CACE estimate restricted to complying schools was in line with ITT, so the null is not merely a compliance artefact. Strong evidence that scalable school PA programs do not raise cognition in practice; weaker evidence about the underlying mechanism, since exposure barely moved.
Genetic confound
Randomization removes genetic confounding; the null contrasts sharply with correlational fitness-cognition associations confounded by shared genetic influence on fitness and g.
Replication notes
Consistent with Ciria 2023's bias-corrected near-null; contrasts with small positive lab meta-analyses.
Effects
| Outcome | Metric | Value | Measure | Timing | Vs | Horizon | Class |
|---|---|---|---|---|---|---|---|
| Maths attainment (primary, preregistered) | Attainment score difference | Null — no significant benefit. This paper reports the result only qualitatively; the estimate itself is in the independent NatCen/EEF evaluation report, not in this article. | standardized | transfer (far); delayed, end of 1 academic year; field | business-as-usual | end-of-treatment | far-transfer |
| Executive function (latent variable) | SMD | 0.017 (95% CI -0.14 to 0.17) | standardized | transfer (far); delayed 1 yr; lab-type tests in field | business-as-usual | end-of-treatment | far-transfer |
| Cardiorespiratory fitness (20-m shuttle run) | SMD | 0.02 (95% CI -0.11 to 0.16) | standardized | retention/end-of-intervention; field | business-as-usual | end-of-treatment | health |
| Relational memory | SMD | -0.10 (95% CI -0.23 to 0.02 per Table 2; the body text of the same paper prints -0.25 to 0.02) | standardized | transfer (far); delayed 1 yr | business-as-usual | end-of-treatment | far-transfer |
| Processing speed | SMD | 0.04 (95% CI -0.07 to 0.15) | standardized | transfer (far); delayed 1 yr | business-as-usual | end-of-treatment | far-transfer |
| Internalising symptoms (SDQ peer + emotional) | SMD | 0.05 (95% CI -0.05 to 0.16) — higher score is worse; null | self-report | end of 1 academic year | business-as-usual | end-of-treatment | non-cognitive |
| Externalising symptoms (SDQ conduct + hyperactivity) | SMD | 0.06 (95% CI -0.03 to 0.16) — higher score is worse; null | self-report | end of 1 academic year | business-as-usual | end-of-treatment | non-cognitive |
| Global self-esteem (PSDQ-S) | SMD | -0.05 (95% CI -0.22 to 0.12) — null; both arms declined from baseline | self-report | end of 1 academic year | business-as-usual | end-of-treatment | non-cognitive |
| Physical self-esteem (PSDQ-S) | SMD | -0.01 (95% CI -0.16 to 0.14) — null | self-report | end of 1 academic year | business-as-usual | end-of-treatment | non-cognitive |
| Delivered dose — accelerometer-measured vigorous PA during a PE lesson (treatment receipt, not an outcome of interest) | minutes VPA per hour of PE | 3.65 (intervention) vs 3.09 (control) full lesson, p=0.23; 4.91 vs 4.38 active lesson, p=0.07 — the intervention did not significantly change the exposure it was designed to change | administrative | single PE lesson during the intervention year | business-as-usual | end-of-treatment | behaviour |
| Change in cardiorespiratory fitness → change in cognition / mental health (mediation test) | association | no significant relationship for any cognitive or mental-health outcome (all corrected p>0.05), and no moderation by treatment group | standardized | 1-year change scores | none | end-of-treatment | far-transfer |
| Moderation by sex, socioeconomic status or baseline fitness | subgroup interaction | no significant moderation after correction (alpha=0.002 for 25 comparisons); 2 of 25 uncorrected p-values fell just below .05 (p=0.04, p=0.03) | standardized | end of 1 academic year | business-as-usual | end-of-treatment | far-transfer |
Cited by
- Does teaching movement transfer to cognition, achievement, or lifelong activity?no effectconf: highgc: medium
- Physical activity as an input — dose, fitness, and school outcomesno effectconf: mediumgc: low