Ten Hoor 2018.

Study characteristics
Methods	Study design: cluster‐RCT
Participants	School inclusion criteria: Dutch secondary schools School exclusion criteria: — Student inclusion criteria: — Student exclusion criteria: — Setting: school Age group: children/adolescents Gender distribution: females and males Country where trial was performed: The Netherlands
Interventions	Intervention: strength training exercises during at least 30% of regular PE lessons, ~ 5 to 30 minutes/lesson. Teachers were instructed about the programme and specific strength exercises and safety guidelines, participated in workshops to improve their motivational speaking skills, were provided with materials (medicine balls, elastic bands, and free weights), and received a book with strength exercises and games. Once a month, a 1‐hour lesson based on motivational interviewing and facilitated by a trained mentor or PE teacher was used to increase motivation to be more physically active  Comparator: continued with  usual curriculum Duration of intervention: 1 year Duration of follow‐up: 1 year Number of schools: 9 Theoretical framework: theory of planned behaviour or reasoned action approach, self‐determination theory, social comparison theory, intervention mapping
Outcomes	PA duration Sedentary time
Study registration	NTR5676
Publication details	Language of publication: English Funding: non‐commercial funding (research funding body) Publication status: peer‐reviewed journal
Stated aim for study	"In this cluster RCT, we investigated the 1‐year efficacy of incorporating strength exercises into gym classes, in combination with monthly motivational lessons (to engage in PAs after school) on the body composition and activity level of adolescents"
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote from publication: "randomised (stratified on education level; by flip of a coin by the first author under supervision of the fourth author) into an intervention condition (4 schools) or a standard curriculum control condition (5 schools)"
Allocation concealment (selection bias)	Low risk	Comment: allocation concealed from schools or directors; informed that they may or may not receive the intervention immediately [author communication]
Blinding of participants and personnel (performance bias) All outcomes	High risk	Comment: not possible [author communication]
Blinding of outcome assessment (detection bias) All outcomes	High risk	Comment: not possible [author communication]
Incomplete outcome data (attrition bias) Physical activity and sedentary time	High risk	Comment: 26% to 28% loss to follow‐up
Selective reporting (reporting bias)	High risk	Comment: strengths listed in clinical trials registry but not reported
Cluster RCT ‐ Recruitment bias	High risk	Comment: students were enrolled and baseline data collected after school randomisation [author communication]
Cluster RCT ‐ Baseline imbalance	Low risk	Quote from publication: "no baseline differences were found between the 2 conditions in age, height, weight, BMI (Z‐score), body composition, or PA outcomes (including wear time of the accelerometer)"
Cluster RCT ‐ Loss of clusters	Low risk	Comment: no loss of clusters
Cluster RCT ‐ Incorrect analysis	Low risk	Quote from publication: "the random (variance) model part consisted of an unstructured covariance matrix for the within‐school variances and covariance of the 2 repeated measures plus a random intercept for the between‐school outcome variance"