Anterior cruciate ligament (ACL) injury constitutes the largest problem in female elite ball/team sport today, due to its relatively high incidence and serious short- and long-term consequences. Especially in handball, these injuries typically occur in actions that are essential for the game, i.e. landings and cutting maneuvers, imposing a challenge for risk reduction strategies. Although knowledge about risk factors is constantly increasing and ACL injury prevention programs have been successful in reducing injuries in rigorous scientific study settings, the real-world injury incidence remains high, and even continues to increase. The purpose of this explorative intervention study is to assess the effect of an eight-week strength and technique training in female handball players and its influence on ACL-specific risk factors, especially knee abduction moment (KAM). The results are compared with a control group that did not do the specially designed technique/muscle training.

BACKGROUND:

ACL injuries are the number one problem in female elite ball/team sports due to its relatively high incidence and serious short- and long-term consequences. Typically injuries occur in actions that are essential for the game, i.e. landings and cutting maneuvers, imposing a challenge for risk reduction strategies.

The consequences of an ACL injury are manifold for the players. They not only reduce quality of life but also lead to a loss of social contacts due to missed training sessions what can be difficult, especially for younger players. Additionally, there are serious long-term consequences with a high likelihood of early osteoarthritis, lasting pain and disability. Also the risk of suffering a second ACL injury after returning to sport is high. In fact, as many as 20-30% of female players returning to play after an ACL injury end up with a new ACL injury in the same or contralateral knee, which makes prevention of a first injury even more important.

Video analyses of ACL injuries strongly suggest that biomechanics is important in injury causation. Novel model-based image-matching techniques have shown that valgus movement occurs shortly after initial contact of the foot with the ground. This implies that knee abduction loading is a likely causative factor. Still, video-based methods have limitations in their accuracy and detail level. To address this knowledge gap, the Oslo Sports Trauma Research Center has carried out the world's largest prospective risk factor study on ACL injuries to date-with multiple data collections between 2007 and 2014.

The most recent analyses indicate that there are clear associations between biomechanics of cutting maneuvers and injury risk. Specifically knee abduction moments seems to be greater in players who later go on to sustain an injury and can be affected by the players' cutting technique variables (width of cut, hip abduction, foot rotation, torso movement/rotation, hip rotation, knee valgus, knee flexion, cutting angle, cutting time, approach speed). These findings may simply reflect that injuries take place in cutting maneuvers and underline the importance of investigating such maneuvers, which closely mimic the real-life setting.

Resulting, there are several different cutting technique strategies, where some strategies may lead to a higher risk for ACL injury while others seem to reduce the risk of injury. Especially landing on the forefoot, rather than on the heel, showed to reduce knee abduction moments by 13% and it was found that a narrow cut, rather than a wide-stance cut, reduced knee abduction moments by 17%.

Based on this knowledge, the investigators want to find out whether it is possible to reduce the players' knee loading, especially reduce KAM, through influencing known risk factors for ACL injuries using a specially designed eight-week muscle and technique training.

AIMS:

The aim of this feasibility study is to assess the effect of an eight-week strength and technique training in female handball players on known risk factors for ACL injuries, especially the knee abduction moment (KAM).

STUDY DESIGN AND METHODS:

To recruit participants, the investigators will contact sports schools in and around Oslo that have a focus on handball. The study is a feasibility study with the aim of finding out whether a targeted, eight-week muscle and technique training based on known ACL-injury risk factors can have a positive influence on their reduction.

At baseline, there will be a 3D motion analysis of all participants (25 in the intervention group, 25 in the control group) performing sidestep cuttings (3 trials per side) in the biomechanical laboratory of the Norwegian School of Sport Sciences (NiH) in Oslo, as well as a strength measurement.

Although a variety of biomechanical data (centre of mass, specific joint positions, cutting width, speed, etc.) is collected as part of the analysis, the focus is on ACL-specific risk factors such as forefoot landing and KAM. The strength test focuses on hip abduction and external rotation, as well as a measurement of the posterior calf muscles.

All players in the intervention group will complete the targeted muscle and technique training integrated into their handball training, while players in the control group only continue their regular handball training. There will be a training of the coaches on site, who assess the training of the intervention group during the entire period and document the participation of the players accordingly.

The strength training consists of three exercises (clam shell, side plank, calf raises) with an progressive overload after two to three weeks to ensure a continuous muscle stimulation. The technique training consists of different cutting variations with a focus on forefoot landings and conscious control of the knee to avoid high knee valgus movement and KAM respectively.

The allocation to intervention or control groups is not random, but separated according to sports schools. This is the only way to ensure that there is no overlapping of training. After a eight-week intervention period, all participants will perform a post-test including the same previous mentioned outcome measures.

Inclusion Criteria:

• Female handball players between the ages of 15 and 18 who go to a sports school in Oslo
• Consent by the players, in the case of age below 16 years by their parents
• Match fitness on test day

Exclusion Criteria:

- History of ACL injury in the last 6 months before baseline testing

ACL injury risk is higher in female handball players. Therefore the investigators want to investigate especially this vulnerable group.

The allocation to intervention or control groups is not random, but separated according to sports schools. This is the only way to ensure that there is no overlapping of training.