BIOMECHANICAL RISK FACTORS FOR ANTERIOR CRUCIATE LIGAMENT INJURY: WHAT DO LANDING TASKS TELL US?

The anterior cruciate ligament (ACL) injury is the most debilitating among the knee structure injuries, in terms of severity and economic burden. It mostly occurs in non-contact situations, during cutting, landing, and pivoting manoeuvres, when the impact to the ground exacerbates the knee load and the tibial shear force. Laboratory tests are commonly adopted to identify athletes predisposed to such injuries, but the results are often inconsistent. The overall aim of this dissertation was to explore the use of landing tasks to assess biomechanical risk factors associated with ACL injuries. The presented protocols included landing tasks with varying features to compare different groups of athletes or to assess the impact of task type on injury-related biomechanics and performance. Sex-related kinematic differences were evaluated in 30 male and 30 female athletes, who were asked to perform a battery of landing tasks. A key aspect was the customization of jump characteristics based on the athletes' anthropometrics and performance levels, minimizing potential confounding factors. A similar approach was adopted to assess sport-related kinematic differences between 22 soccer and 19 volleyball players; in this case, the customized task battery included uniplanar and multiplanar landings, to simulate the sport-specific ACL injury mechanisms. In both projects, statistical models were used to assess the main kinematic variables, considering the instant of ground contact and the peak reached while landing, which are commonly associated with ACL injury. Sex-related kinematic differences emerged, although tasks were customized, but we found non-significant sport-related differences. The multiplanar tasks, included in these projects and in other past studies, are often characterized by combined jumps, but the impact of the secondary jump direction had not been fully analysed yet. For this purpose, the same participants were involved to analyse the entire time series of landing kinematics using the Statistical Parametric Mapping. Thanks to this approach, the observed direction-related differences highlighted how important it is to consider the task type before drawing conclusions about an athlete's risk. Another aspect of ACL injury considered in this thesis was the influence of cognitive abilities on anticipated and unanticipated landing tasks. The cognitive abilities of 10 athletes were assessed using a novel motor-cognitive test battery, allowing the evaluation of athletes’ ability to apply these skills in sport gestures. Motor-cognitive scores seemed to be associated with potentially detrimental movements and the cognitive loads in unanticipated tasks affected lower limb biomechanics, reinforcing the importance of evaluating cognitive performance to mitigate injury risks during athletic performance. Finally, the conflict between ACL injury prevention and jump performance was investigated including 31 athletes, evaluating the effect of a cushioned (soft) landing on both kinematics and jumping metrics, with respect to unrestricted and fast techniques. The findings confirmed that a soft landing was beneficial, as the increased knee flexion protects the ACL from excessive loads, but highlighted its potential drawbacks on jump height and contact time, underlining a plausible trade-off between preventing ACL injuries while improving performance. The fil rouge connecting the conclusions of each section of this dissertation was that not all tests are suitable for every individual, and several factors must be considered, such as sex, sport, test characteristics, and cognitive aspects. Although we are still far from having standardized methods for identifying athletes at risk, advancements in research and technology are improving, making ACL injury rate reduction increasingly achievable.