This study evaluates the effects of two different injury prevention exercise programs on sports-relevant performance tests and neuromuscular function in youth football players. Half of participants will receive education on an existing and previously tested exercise program, while the other half will receive education on a newly developed exercise program.

Injury prevention exercise programs have been developed for a variety of sporting contexts and many have proven to be efficacious in preventing injuries. Adherence with the training may, however, be an issue and poor adherence may limit the preventive effect. If using the preventive exercise programs can be shown to improve sports-relevant performance this may motivate both coaches and players to use these programs, since the reduction in injury risk is harder to notice for the individual.

This study focuses on a Swedish injury prevention exercise program called Knee Control. The program has been found efficacious in preventing acute knee injuries in girls' adolescent football players in previous trials. We have found, however, that coaches often modify the Knee Control program to improve program fit and player buy-in among female youth football players. Careful changes must be made to the program since there is a risk of compromising the preventive effect and the effect on performance if the training dose is too low or if effective exercises are replaced with other exercises. We have therefore further developed the Knee Control program, to a Knee Control+ program, to support the coaches in the tailoring of the program to preserve the preventive effect and hopefully enhance performance effects. By introducing more variation with easier and more difficult exercises, pair-exercises, competitive and plyometric elements the new Knee Control+ program may better fit both the youngest and the oldest players, which in turn may facilitate fidelity with and maintenance of the program.

The aim of the study is to compare the neuromuscular and performance effects of the original Knee Control and the new Knee Control+ programs among youth female and male football players. A secondary aim is to study player and coach experiences of the programs and their fidelity with the training protocol.

Hypothesis: We expect similar effects of both programs, or superior effects of the Knee Control+ program, showing that the programs are compatible but the program adherence and fidelity being better with Knee Control+.

Methods: Eight youth football teams (4 boys, 4 girls, age 13-17 years) with approximately 120 players will be included in the study. Four teams will receive education about the Knee Control program and four teams about the Knee Control+ program. All coaches and two to three players per team will take part in a workshop at baseline where registered physiotherapists will give practical instructions of the intervention exercise programs. The workshops will also contain theoretical information about injuries in football and the background for either the Knee Control or the Knee Control+ programs. The attending coaches and players will be able to test all exercises and receive feedback about correct movement technique.

Outcomes: Football-relevant performance and neuromuscular function will be tested at baseline and after 12 weeks of training.

Inclusion Criteria:

• Football teams who have training at least twice per week
• Healthy players who can exert themselves maximally during testing

Exclusion Criteria:

• Teams who have used the Knee Control or a similar injury prevention exercise program on a regular basis the last year
• Players who cannot take full part in measurements due to illnesses or injuries

Study data (de-identified player performance test scores) may be available at request from the principal investigator

Outcomes assessors (performance tests and neuromuscular function) blinded to group allocation