FIT FIRST teen–a cluster RCT evaluating the effects of a 10-week high-intensity exercise intervention for 12–15-yr-old school children

Objectives: To evaluate the effects of a 10-week thrice-weekly FIT FIRST Teen (FFT) intervention on cardiorespiratory fitness in Danish 12–15-years-olds.

Design: A cluster-randomised controlled study.

Participants: One thousand four hundred and seventeen Danish pupils (51.1% female) from 15 municipal schools, allocated to an intervention group (FFT: n = 994, 13.5 (0.6) years (mean (SD)), 165.8 (8.7) cm, 57.8 (13.4) kg) or a usual practice control group (CON: n = 423, 13.8 (0.8) years, 167.7 (11.5) cm, 58.6 (12.2) kg).

Methods: The FFT group completed three weekly 40-min FFT sessions with modified, motivating, involving, high-intensity sports-based activities. Before and after the 10-wk intervention period resting heart rate and blood pressure, body composition, postural balance, standing long jump and performance on the Yo–Yo intermittent recovery level 1 children’s test (YYIR1C) were measured. Group effects for all outcome variables were tested using multi-level linear mixed models.

Results: The group effect analyses showed no significant differences between FFT and CON in the YYIR1C test (p = 0.080). A significant small difference between groups was found in resting heart rate (d = 0.29, p = 0.039) in favour of FFT. No significant between-group differences were observed in body composition, or the remaining cardiovascular or physical fitness variables (p >0.05).

Conclusion: The lack of significant effects for the majority of the outcome measures calls for further development and long-term testing of the programme.