The Influence of Neuromuscular Training on Whole-body Movement Strategies and Knee Mechanics During Change-of-direction Tasks in Sports Science Students

Detailed Summary

Background Knee injuries are common during sports that require fast change-of-direction (COD) movements such as sidestepping and pivoting during soccer, basketball, handball, and related sports. COD movements expose the knee joint to large external forces, particularly if players show a poor COD technique such as lateral trunk lean towards the plant foot or a strong knee valgus of the cutting leg. Larger external forces and moments that act on the knee joint are expected to result in larger strain of the anterior cruciate ligament (ACL) and thus a higher risk of ACL rupture. Consequently, during sports like soccer and basketball, many non-contact ACL injuries occur during COD tasks. While neuromuscular training (NMT) programs have been developed to effectively reduce the risk of sports injury including ACL tears, ACL injury rates have not declined in the last years. One of the reasons for this paradox may be that many NMT programs such as the FIFA11+ program, which were developed to protect from injury do not actually improve COD movement strategies. It may be assumed that FIFA11+ does reduce the overall risk of sports injury through general improvements in strength and balance as well as safer jump landing technique but not through safer COD technique. Further, if training interventions were successful in reducing 'high-risk' movement patterns and in developing knee-stabilizing muscle synergies during COD movements, it remains unclear whether the improved movement strategy, e.g. the reduction in external knee valgus moments, actually corresponds to reduced ACL strain. In consequence, there is the need for a comprehensive investigation to determine whether a NMT program focused on improving COD technique will improve COD movement and muscle activation strategies and whether these improvements are correlated with estimated ACL strain. A second reason for the paradox may be that current experimental protocols to investigate COD movement strategies in the laboratory are not a good indicator for actual player behavior on the field thus masking potential benefits of NMT on lateral movements. Therefore, the sports injury prevention community should aim to move the assessment of COD movement strategy onto the playing field and into a more realistic playing environment while characterizing the kinematics and kinetics of sidestepping based on wearable sensors. In consequence, novel analytical frameworks based on wearables need to be developed, which can capture full-body kinematics and the underlying forces during COD movements on the playing field. In the long run, such systems could facilitate real-time feedback with respect to COD technique on the playing field and thus enhance motor learning of the players as well as characterize real-world player agility. Research objectives \& hypotheses Objective 1: To determine the effect of an 8-week NMT and COD technique modification intervention (multidirection training, MD) on 1) COD movement strategies as characterized by the lateral trunk angle and knee valgus moment and 2) estimated ACL strain during 45- and 135-degree COD movements in comparison to an 8-week NMT and linear sprint training intervention (linear sprint training, LS) in sports science students. Hypothesis 1: There will be a larger reduction in lateral trunk angle and knee valgus moment and an associated reduction in ACL strain in the MD group compared to the LS group following the 8-week intervention, which will be retained four weeks later. Objective 2: To determine the effect of an 8-week NMT and COD technique modification intervention on leg muscle synergies as characterized by the number of muscles and the structure of the synergy vector for each identified muscle synergy in comparison to an 8-week NMT and linear sprint training intervention in sports science students. Hypothesis 2: One or multiple muscle synergy vectors will show an increased contribution of hip abductor muscle activity in the MD group following training and there will be a lower number of activated muscles per identified synergy, i.e. a more selective muscle activation in comparison to the LS group. These improvements will be retained four weeks later. Objective 3: To determine the validity of an analysis framework to estimate COD movement strategy (lateral trunk angle, foot progression angle, knee valgus moment) and ACL strain based solely on inertial motion capture data in comparison to the gold-standard of 3D optimal motion capture.

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