Low-volume high-intensity interval exercise training may improve aspects of health and fitness in young people, but the effect of this type of exercise on quality of life has yet to be assessed. The investigators aim to examine the effect of a 4-week school-based low-volume high-intensity interval training programme (called the Fun Fast Interval Training [FFIT] activity project) on physical fitness and quality of life in adolescent school pupils. Approximately 145 English adolescents aged 11-12 years will be approached and invited to take part in the study. Participants will be healthy female volunteers, recruited from one school in Northeast England. Using a non-randomised design, one school year group will be assigned to take part in the intervention, and a second year group assigned to the control condition.Those in the intervention group will complete a 4-week school-based high-intensity interval exercise training programme. The intervention will take place twice per week, and comprise of 6-8 repetitions of 45 s maximal effort exercise (boxing, running, soccer and basketball drills), each interspersed with 90-s rest. Participants will be encouraged to work maximally during the 45-s repetitions. Control participants will be instructed not to change their lifestyle, dietary or physical activity habits during the intervention period, and maintain their normal school physical education routine. Study outcomes will be 20 m shuttle run test performance, health-related quality of life, standing broad jump performance, hand dynamometer performance, waist circumference and 10 m and 20 m sprint performance.