Original article written by Stefano Di Paolo, Eline Nijmeijer, Laura Bragonzoni and colleagues.
Background
Anterior cruciate ligament (ACL) injuries are very serious for team sport athletes, and commonly occur during agility actions in match play. There is a higher risk of ACL rupture in female team sport athletes, compared to males. Considerable research has focussed on biomechanical risk factors in a laboratory setting, where the participants are required to perform a pre-planned cutting task with prior knowledge of the directional change and technique to be executed. Some laboratory studies also use unanticipated changes of direction where the athlete reacts to a non sport-specific stimulus such as a flashing light. However, ACL injuries occur in game situations where the agility task is more complex and varied. This means that laboratory-based biomechanical studies may observe different movement strategies to what occurs on the field or court. Therefore, the aim of this study was to compare the lower-limb kinematics of female footballers (soccer) during agility movements performed in a laboratory environment to on a football field.
What the authors did
The participants were 28 female soccer players from either the highest or second highest level in the Netherlands. The players performed three different tasks (Figure 1).
The biomechanical analysis was achieved by fitting players with a Lycra suit which contained 17 inertial measurement units (IMU’s) over the body.
What the authors found
The most important finding of the current study was the presence of kinematic differences between the movements performed in the laboratory and on the field, regardless of the three tasks. Further, the differences in sagittal plane range of motion, ankle eversion, and pelvis rotations are linked to ACL injury mechanisms and preventative strategies. The authors also reported more movement variability in agility technique in the field tasks compared to the lab setting.
Limitations
The main limitation of this study was that the cut angles and approach speeds were not standardised for all three conditions. On the other hand, this can be seen as a positive feature because it allows us to observe differences between contexts (lab vs. field).
What this means for coaches
The kinematic differences across the three tasks have implications for ACL prevention strategies. Players adapt their movement patterns in response to increasing environmental complexity e.g. unpredictability. The authors recommended an ecological dynamics approach where learners are encouraged to use variable patterns to find their own optimum movement solutions to the ever-changing environment on the field (See Bolt and colleagues [1]).
Reviewer’s comments
A key point to take from this study is that agility technique and movement strategies naturally change in a game-like chaotic environment as found in football. Conversely, training agility techniques that are predictable with limited variability are unlikely to prepare players for the unpredictability seen on the field. This in turn, would not allow players to be adaptable to the high pressure demands of match play, and may place them in sub-optimum body positions that could increase ACL injury risk. Although this study was novel in assessing biomechanical variables with IMU’s in field conditions, an older study by Sayers and Wheeler [2] also demonstrated that rugby players altered their agility technique when confronted with a defensive opponent in a sport-specific scenario, compared to a pre-planned sidestepping task. They concluded that rugby players should train agility in a sport-specific environment to ensure appropriate footwork is used.
Recommended resoucese
Article – Improving agility performance through technical and physical development – Warren Young