Flywheel Squats Versus Free Weight High Load Squats for Explosive Actions in Football

The investigators will aim at recruiting 45 recreationally active football players, that will be randomly allocated to three groups: 1) flywheel (FW) group (n=15), 2) barbell free weight (BFW) group (n=15) and 3) control group (n=15).The FW and the BFW group will participate in an intervention where they perform a squat exercise either with a FW device or with BFWs twice a week over six weeks (in total 12 sessions) as a part of their preseason preparations. The control group will be instructed to not perform lower body resistance exercise and only to perform their teams' preseason preparations and acted as controls. During the intervention period, all players in all groups will be instructed to avoid other resistance exercises for their lower body, while no restrictions will be given in regard to resistance exercises for their upper body in their spare time.

This study will be carried out in accordance with international ethical standards for sport and exercise science and to the Declaration of Helsinki; prior to pre-tests, all the players will be informed of the purpose of the study and its associated risks and benefits, before providing oral and written informed consent. The Norwegian Data Protection Service has approved the study and the storage of personal data (Approval reference number: 374030). No further Regional Ethical approval per applicable institutional and national guidelines for sport and exercise science.

Prior to the interventions, the players will undergo pre-tests in the following order on the same test day: 1) 10 meter sprint time, 2) CMJ and 3) 1RM in a free barbell partial squat, carried out as 90° ROM in the knee joint (standing position = 180°).

10 meter sprint: The 10 meter sprint test will be performed on artificial grass indoors. Photocells mounted to the floor and walls recorded the sprint times, where the photocells at the starting and the finishing line are placed 20 cm and 100 cm above the ground, respectively. A marker is placed 30 cm behind of the starting timing gate, where the players chose their starting position behind the marker. The players starts their test on their own initiative, and without verbal encouragement, by breaking the laser beam at the starting timing gate and sprinted to the finishing line as fast as they can. Each player is given three attempts with three minutes recovery between each sprint.

Countermovement jump: